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INFO-DIR-SECTION Programming Languages START-INFO-DIR-ENTRY * Gawk: (gawk.info). A Text Scanning and Processing Language. END-INFO-DIR-ENTRY This file documents `awk', a program that you can use to select particular records in a file and perform operations upon them. This is Edition 1.0.3 of `Effective AWK Programming', for the 3.0.3 version of the GNU implementation of AWK. Copyright (C) 1989, 1991, 92, 93, 96, 97 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation.  File: gawk.info, Node: Top, Next: Preface, Prev: (dir), Up: (dir) General Introduction ******************** This file documents `awk', a program that you can use to select particular records in a file and perform operations upon them. This is Edition 1.0.3 of `Effective AWK Programming', for the 3.0.3 version of the GNU implementation of AWK. * Menu: * Preface:: What this Info file is about; brief history and acknowledgements. * What Is Awk:: What is the `awk' language; using this Info file. * Getting Started:: A basic introduction to using `awk'. How to run an `awk' program. Command line syntax. * One-liners:: Short, sample `awk' programs. * Regexp:: All about matching things using regular expressions. * Reading Files:: How to read files and manipulate fields. * Printing:: How to print using `awk'. Describes the `print' and `printf' statements. Also describes redirection of output. * Expressions:: Expressions are the basic building blocks of statements. * Patterns and Actions:: Overviews of patterns and actions. * Statements:: The various control statements are described in detail. * Built-in Variables:: Built-in Variables * Arrays:: The description and use of arrays. Also includes array-oriented control statements. * Built-in:: The built-in functions are summarized here. * User-defined:: User-defined functions are described in detail. * Invoking Gawk:: How to run `gawk'. * Library Functions:: A Library of `awk' Functions. * Sample Programs:: Many `awk' programs with complete explanations. * Language History:: The evolution of the `awk' language. * Gawk Summary:: `gawk' Options and Language Summary. * Installation:: Installing `gawk' under various operating systems. * Notes:: Something about the implementation of `gawk'. * Glossary:: An explanation of some unfamiliar terms. * Copying:: Your right to copy and distribute `gawk'. * Index:: Concept and Variable Index. * History:: The history of `gawk' and `awk'. * Manual History:: Brief history of the GNU project and this Info file. * Acknowledgements:: Acknowledgements. * This Manual:: Using this Info file. Includes sample input files that you can use. * Conventions:: Typographical Conventions. * Sample Data Files:: Sample data files for use in the `awk' programs illustrated in this Info file. * Names:: What name to use to find `awk'. * Running gawk:: How to run `gawk' programs; includes command line syntax. * One-shot:: Running a short throw-away `awk' program. * Read Terminal:: Using no input files (input from terminal instead). * Long:: Putting permanent `awk' programs in files. * Executable Scripts:: Making self-contained `awk' programs. * Comments:: Adding documentation to `gawk' programs. * Very Simple:: A very simple example. * Two Rules:: A less simple one-line example with two rules. * More Complex:: A more complex example. * Statements/Lines:: Subdividing or combining statements into lines. * Other Features:: Other Features of `awk'. * When:: When to use `gawk' and when to use other things. * Regexp Usage:: How to Use Regular Expressions. * Escape Sequences:: How to write non-printing characters. * Regexp Operators:: Regular Expression Operators. * GNU Regexp Operators:: Operators specific to GNU software. * Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. * Records:: Controlling how data is split into records. * Fields:: An introduction to fields. * Non-Constant Fields:: Non-constant Field Numbers. * Changing Fields:: Changing the Contents of a Field. * Field Separators:: The field separator and how to change it. * Basic Field Splitting:: How fields are split with single characters or simple strings. * Regexp Field Splitting:: Using regexps as the field separator. * Single Character Fields:: Making each character a separate field. * Command Line Field Separator:: Setting `FS' from the command line. * Field Splitting Summary:: Some final points and a summary table. * Constant Size:: Reading constant width data. * Multiple Line:: Reading multi-line records. * Getline:: Reading files under explicit program control using the `getline' function. * Getline Intro:: Introduction to the `getline' function. * Plain Getline:: Using `getline' with no arguments. * Getline/Variable:: Using `getline' into a variable. * Getline/File:: Using `getline' from a file. * Getline/Variable/File:: Using `getline' into a variable from a file. * Getline/Pipe:: Using `getline' from a pipe. * Getline/Variable/Pipe:: Using `getline' into a variable from a pipe. * Getline Summary:: Summary Of `getline' Variants. * Print:: The `print' statement. * Print Examples:: Simple examples of `print' statements. * Output Separators:: The output separators and how to change them. * OFMT:: Controlling Numeric Output With `print'. * Printf:: The `printf' statement. * Basic Printf:: Syntax of the `printf' statement. * Control Letters:: Format-control letters. * Format Modifiers:: Format-specification modifiers. * Printf Examples:: Several examples. * Redirection:: How to redirect output to multiple files and pipes. * Special Files:: File name interpretation in `gawk'. `gawk' allows access to inherited file descriptors. * Close Files And Pipes:: Closing Input and Output Files and Pipes. * Constants:: String, numeric, and regexp constants. * Scalar Constants:: Numeric and string constants. * Regexp Constants:: Regular Expression constants. * Using Constant Regexps:: When and how to use a regexp constant. * Variables:: Variables give names to values for later use. * Using Variables:: Using variables in your programs. * Assignment Options:: Setting variables on the command line and a summary of command line syntax. This is an advanced method of input. * Conversion:: The conversion of strings to numbers and vice versa. * Arithmetic Ops:: Arithmetic operations (`+', `-', etc.) * Concatenation:: Concatenating strings. * Assignment Ops:: Changing the value of a variable or a field. * Increment Ops:: Incrementing the numeric value of a variable. * Truth Values:: What is "true" and what is "false". * Typing and Comparison:: How variables acquire types, and how this affects comparison of numbers and strings with `<', etc. * Boolean Ops:: Combining comparison expressions using boolean operators `||' ("or"), `&&' ("and") and `!' ("not"). * Conditional Exp:: Conditional expressions select between two subexpressions under control of a third subexpression. * Function Calls:: A function call is an expression. * Precedence:: How various operators nest. * Pattern Overview:: What goes into a pattern. * Kinds of Patterns:: A list of all kinds of patterns. * Regexp Patterns:: Using regexps as patterns. * Expression Patterns:: Any expression can be used as a pattern. * Ranges:: Pairs of patterns specify record ranges. * BEGIN/END:: Specifying initialization and cleanup rules. * Using BEGIN/END:: How and why to use BEGIN/END rules. * I/O And BEGIN/END:: I/O issues in BEGIN/END rules. * Empty:: The empty pattern, which matches every record. * Action Overview:: What goes into an action. * If Statement:: Conditionally execute some `awk' statements. * While Statement:: Loop until some condition is satisfied. * Do Statement:: Do specified action while looping until some condition is satisfied. * For Statement:: Another looping statement, that provides initialization and increment clauses. * Break Statement:: Immediately exit the innermost enclosing loop. * Continue Statement:: Skip to the end of the innermost enclosing loop. * Next Statement:: Stop processing the current input record. * Nextfile Statement:: Stop processing the current file. * Exit Statement:: Stop execution of `awk'. * User-modified:: Built-in variables that you change to control `awk'. * Auto-set:: Built-in variables where `awk' gives you information. * ARGC and ARGV:: Ways to use `ARGC' and `ARGV'. * Array Intro:: Introduction to Arrays * Reference to Elements:: How to examine one element of an array. * Assigning Elements:: How to change an element of an array. * Array Example:: Basic Example of an Array * Scanning an Array:: A variation of the `for' statement. It loops through the indices of an array's existing elements. * Delete:: The `delete' statement removes an element from an array. * Numeric Array Subscripts:: How to use numbers as subscripts in `awk'. * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. * Multi-dimensional:: Emulating multi-dimensional arrays in `awk'. * Multi-scanning:: Scanning multi-dimensional arrays. * Calling Built-in:: How to call built-in functions. * Numeric Functions:: Functions that work with numbers, including `int', `sin' and `rand'. * String Functions:: Functions for string manipulation, such as `split', `match', and `sprintf'. * I/O Functions:: Functions for files and shell commands. * Time Functions:: Functions for dealing with time stamps. * Definition Syntax:: How to write definitions and what they mean. * Function Example:: An example function definition and what it does. * Function Caveats:: Things to watch out for. * Return Statement:: Specifying the value a function returns. * Options:: Command line options and their meanings. * Other Arguments:: Input file names and variable assignments. * AWKPATH Variable:: Searching directories for `awk' programs. * Obsolete:: Obsolete Options and/or features. * Undocumented:: Undocumented Options and Features. * Known Bugs:: Known Bugs in `gawk'. * Portability Notes:: What to do if you don't have `gawk'. * Nextfile Function:: Two implementations of a `nextfile' function. * Assert Function:: A function for assertions in `awk' programs. * Round Function:: A function for rounding if `sprintf' does not do it correctly. * Ordinal Functions:: Functions for using characters as numbers and vice versa. * Join Function:: A function to join an array into a string. * Mktime Function:: A function to turn a date into a timestamp. * Gettimeofday Function:: A function to get formatted times. * Filetrans Function:: A function for handling data file transitions. * Getopt Function:: A function for processing command line arguments. * Passwd Functions:: Functions for getting user information. * Group Functions:: Functions for getting group information. * Library Names:: How to best name private global variables in library functions. * Clones:: Clones of common utilities. * Cut Program:: The `cut' utility. * Egrep Program:: The `egrep' utility. * Id Program:: The `id' utility. * Split Program:: The `split' utility. * Tee Program:: The `tee' utility. * Uniq Program:: The `uniq' utility. * Wc Program:: The `wc' utility. * Miscellaneous Programs:: Some interesting `awk' programs. * Dupword Program:: Finding duplicated words in a document. * Alarm Program:: An alarm clock. * Translate Program:: A program similar to the `tr' utility. * Labels Program:: Printing mailing labels. * Word Sorting:: A program to produce a word usage count. * History Sorting:: Eliminating duplicate entries from a history file. * Extract Program:: Pulling out programs from Texinfo source files. * Simple Sed:: A Simple Stream Editor. * Igawk Program:: A wrapper for `awk' that includes files. * V7/SVR3.1:: The major changes between V7 and System V Release 3.1. * SVR4:: Minor changes between System V Releases 3.1 and 4. * POSIX:: New features from the POSIX standard. * BTL:: New features from the Bell Laboratories version of `awk'. * POSIX/GNU:: The extensions in `gawk' not in POSIX `awk'. * Command Line Summary:: Recapitulation of the command line. * Language Summary:: A terse review of the language. * Variables/Fields:: Variables, fields, and arrays. * Fields Summary:: Input field splitting. * Built-in Summary:: `awk''s built-in variables. * Arrays Summary:: Using arrays. * Data Type Summary:: Values in `awk' are numbers or strings. * Rules Summary:: Patterns and Actions, and their component parts. * Pattern Summary:: Quick overview of patterns. * Regexp Summary:: Quick overview of regular expressions. * Actions Summary:: Quick overview of actions. * Operator Summary:: `awk' operators. * Control Flow Summary:: The control statements. * I/O Summary:: The I/O statements. * Printf Summary:: A summary of `printf'. * Special File Summary:: Special file names interpreted internally. * Built-in Functions Summary:: Built-in numeric and string functions. * Time Functions Summary:: Built-in time functions. * String Constants Summary:: Escape sequences in strings. * Functions Summary:: Defining and calling functions. * Historical Features:: Some undocumented but supported "features". * Gawk Distribution:: What is in the `gawk' distribution. * Getting:: How to get the distribution. * Extracting:: How to extract the distribution. * Distribution contents:: What is in the distribution. * Unix Installation:: Installing `gawk' under various versions of Unix. * Quick Installation:: Compiling `gawk' under Unix. * Configuration Philosophy:: How it's all supposed to work. * VMS Installation:: Installing `gawk' on VMS. * VMS Compilation:: How to compile `gawk' under VMS. * VMS Installation Details:: How to install `gawk' under VMS. * VMS Running:: How to run `gawk' under VMS. * VMS POSIX:: Alternate instructions for VMS POSIX. * PC Installation:: Installing and Compiling `gawk' on MS-DOS and OS/2 * Atari Installation:: Installing `gawk' on the Atari ST. * Atari Compiling:: Compiling `gawk' on Atari * Atari Using:: Running `gawk' on Atari * Amiga Installation:: Installing `gawk' on an Amiga. * Bugs:: Reporting Problems and Bugs. * Other Versions:: Other freely available `awk' implementations. * Compatibility Mode:: How to disable certain `gawk' extensions. * Additions:: Making Additions To `gawk'. * Adding Code:: Adding code to the main body of `gawk'. * New Ports:: Porting `gawk' to a new operating system. * Future Extensions:: New features that may be implemented one day. * Improvements:: Suggestions for improvements by volunteers. To Miriam, for making me complete. To Chana, for the joy you bring us. To Rivka, for the exponential increase. To Nachum, for the added dimension.  File: gawk.info, Node: Preface, Next: What Is Awk, Prev: Top, Up: Top Preface ******* This Info file teaches you about the `awk' language and how you can use it effectively. You should already be familiar with basic system commands, such as `cat' and `ls',(1) and basic shell facilities, such as Input/Output (I/O) redirection and pipes. Implementations of the `awk' language are available for many different computing environments. This Info file, while describing the `awk' language in general, also describes a particular implementation of `awk' called `gawk' (which stands for "GNU Awk"). `gawk' runs on a broad range of Unix systems, ranging from 80386 PC-based computers, up through large scale systems, such as Crays. `gawk' has also been ported to MS-DOS and OS/2 PC's, Atari and Amiga micro-computers, and VMS. * Menu: * History:: The history of `gawk' and `awk'. * Manual History:: Brief history of the GNU project and this Info file. * Acknowledgements:: Acknowledgements. ---------- Footnotes ---------- (1) These commands are available on POSIX compliant systems, as well as on traditional Unix based systems. If you are using some other operating system, you still need to be familiar with the ideas of I/O redirection and pipes.  File: gawk.info, Node: History, Next: Manual History, Prev: Preface, Up: Preface History of `awk' and `gawk' =========================== The name `awk' comes from the initials of its designers: Alfred V. Aho, Peter J. Weinberger, and Brian W. Kernighan. The original version of `awk' was written in 1977 at AT&T Bell Laboratories. In 1985 a new version made the programming language more powerful, introducing user-defined functions, multiple input streams, and computed regular expressions. This new version became generally available with Unix System V Release 3.1. The version in System V Release 4 added some new features and also cleaned up the behavior in some of the "dark corners" of the language. The specification for `awk' in the POSIX Command Language and Utilities standard further clarified the language based on feedback from both the `gawk' designers, and the original Bell Labs `awk' designers. The GNU implementation, `gawk', was written in 1986 by Paul Rubin and Jay Fenlason, with advice from Richard Stallman. John Woods contributed parts of the code as well. In 1988 and 1989, David Trueman, with help from Arnold Robbins, thoroughly reworked `gawk' for compatibility with the newer `awk'. Current development focuses on bug fixes, performance improvements, standards compliance, and occasionally, new features.  File: gawk.info, Node: Manual History, Next: Acknowledgements, Prev: History, Up: Preface The GNU Project and This Book ============================= The Free Software Foundation (FSF) is a non-profit organization dedicated to the production and distribution of freely distributable software. It was founded by Richard M. Stallman, the author of the original Emacs editor. GNU Emacs is the most widely used version of Emacs today. The GNU project is an on-going effort on the part of the Free Software Foundation to create a complete, freely distributable, POSIX compliant computing environment. (GNU stands for "GNU's not Unix".) The FSF uses the "GNU General Public License" (or GPL) to ensure that source code for their software is always available to the end user. A copy of the GPL is included for your reference (*note GNU GENERAL PUBLIC LICENSE: Copying.). The GPL applies to the C language source code for `gawk'. A shell, an editor (Emacs), highly portable optimizing C, C++, and Objective-C compilers, a symbolic debugger, and dozens of large and small utilities (such as `gawk'), have all been completed and are freely available. As of this writing (early 1997), the GNU operating system kernel (the HURD), has been released, but is still in an early stage of development. Until the GNU operating system is more fully developed, you should consider using Linux, a freely distributable, Unix-like operating system for 80386, DEC Alpha, Sun SPARC and other systems. There are many books on Linux. One freely available one is `Linux Installation and Getting Started', by Matt Welsh. Many Linux distributions are available, often in computer stores or bundled on CD-ROM with books about Linux. (There are three other freely available, Unix-like operating systems for 80386 and other systems, NetBSD, FreeBSD,and OpenBSD. All are based on the 4.4-Lite Berkeley Software Distribution, and they use recent versions of `gawk' for their versions of `awk'.) This Info file itself has gone through several previous, preliminary editions. I started working on a preliminary draft of `The GAWK Manual', by Diane Close, Paul Rubin, and Richard Stallman in the fall of 1988. It was around 90 pages long, and barely described the original, "old" version of `awk'. After substantial revision, the first version of the `The GAWK Manual' to be released was Edition 0.11 Beta in October of 1989. The manual then underwent more substantial revision for Edition 0.13 of December 1991. David Trueman, Pat Rankin, and Michal Jaegermann contributed sections of the manual for Edition 0.13. That edition was published by the FSF as a bound book early in 1992. Since then there have been several minor revisions, notably Edition 0.14 of November 1992 that was published by the FSF in January of 1993, and Edition 0.16 of August 1993. Edition 1.0 of `Effective AWK Programming' represents a significant re-working of `The GAWK Manual', with much additional material. The FSF and I agree that I am now the primary author. I also felt that it needed a more descriptive title. `Effective AWK Programming' will undoubtedly continue to evolve. An electronic version comes with the `gawk' distribution from the FSF. If you find an error in this Info file, please report it! *Note Reporting Problems and Bugs: Bugs, for information on submitting problem reports electronically, or write to me in care of the FSF.  File: gawk.info, Node: Acknowledgements, Prev: Manual History, Up: Preface Acknowledgements ================ I would like to acknowledge Richard M. Stallman, for his vision of a better world, and for his courage in founding the FSF and starting the GNU project. The initial draft of `The GAWK Manual' had the following acknowledgements: Many people need to be thanked for their assistance in producing this manual. Jay Fenlason contributed many ideas and sample programs. Richard Mlynarik and Robert Chassell gave helpful comments on drafts of this manual. The paper `A Supplemental Document for `awk'' by John W. Pierce of the Chemistry Department at UC San Diego, pinpointed several issues relevant both to `awk' implementation and to this manual, that would otherwise have escaped us. The following people provided many helpful comments on Edition 0.13 of `The GAWK Manual': Rick Adams, Michael Brennan, Rich Burridge, Diane Close, Christopher ("Topher") Eliot, Michael Lijewski, Pat Rankin, Miriam Robbins, and Michal Jaegermann. The following people provided many helpful comments for Edition 1.0 of `Effective AWK Programming': Karl Berry, Michael Brennan, Darrel Hankerson, Michal Jaegermann, Michael Lijewski, and Miriam Robbins. Pat Rankin, Michal Jaegermann, Darrel Hankerson and Scott Deifik updated their respective sections for Edition 1.0. Robert J. Chassell provided much valuable advice on the use of Texinfo. He also deserves special thanks for convincing me *not* to title this Info file `How To Gawk Politely'. Karl Berry helped significantly with the TeX part of Texinfo. David Trueman deserves special credit; he has done a yeoman job of evolving `gawk' so that it performs well, and without bugs. Although he is no longer involved with `gawk', working with him on this project was a significant pleasure. Scott Deifik, Darrel Hankerson, Kai Uwe Rommel, Pat Rankin, and Michal Jaegermann (in no particular order) are long time members of the `gawk' "crack portability team." Without their hard work and help, `gawk' would not be nearly the fine program it is today. It has been and continues to be a pleasure working with this team of fine people. Jeffrey Friedl provided invaluable help in tracking down a number of last minute problems with regular expressions in `gawk' 3.0. David and I would like to thank Brian Kernighan of Bell Labs for invaluable assistance during the testing and debugging of `gawk', and for help in clarifying numerous points about the language. We could not have done nearly as good a job on either `gawk' or its documentation without his help. I would like to thank Marshall and Elaine Hartholz of Seattle, and Dr. Bert and Rita Schreiber of Detroit for large amounts of quiet vacation time in their homes, which allowed me to make significant progress on this Info file and on `gawk' itself. Phil Hughes of SSC contributed in a very important way by loaning me his laptop Linux system, not once, but twice, allowing me to do a lot of work while away from home. Finally, I must thank my wonderful wife, Miriam, for her patience through the many versions of this project, for her proof-reading, and for sharing me with the computer. I would like to thank my parents for their love, and for the grace with which they raised and educated me. I also must acknowledge my gratitude to G-d, for the many opportunities He has sent my way, as well as for the gifts He has given me with which to take advantage of those opportunities. Arnold Robbins Atlanta, Georgia February, 1997  File: gawk.info, Node: What Is Awk, Next: Getting Started, Prev: Preface, Up: Top Introduction ************ If you are like many computer users, you would frequently like to make changes in various text files wherever certain patterns appear, or extract data from parts of certain lines while discarding the rest. To write a program to do this in a language such as C or Pascal is a time-consuming inconvenience that may take many lines of code. The job may be easier with `awk'. The `awk' utility interprets a special-purpose programming language that makes it possible to handle simple data-reformatting jobs with just a few lines of code. The GNU implementation of `awk' is called `gawk'; it is fully upward compatible with the System V Release 4 version of `awk'. `gawk' is also upward compatible with the POSIX specification of the `awk' language. This means that all properly written `awk' programs should work with `gawk'. Thus, we usually don't distinguish between `gawk' and other `awk' implementations. Using `awk' you can: * manage small, personal databases * generate reports * validate data * produce indexes, and perform other document preparation tasks * even experiment with algorithms that can be adapted later to other computer languages * Menu: * This Manual:: Using this Info file. Includes sample input files that you can use. * Conventions:: Typographical Conventions. * Sample Data Files:: Sample data files for use in the `awk' programs illustrated in this Info file.  File: gawk.info, Node: This Manual, Next: Conventions, Prev: What Is Awk, Up: What Is Awk Using This Book =============== The term `awk' refers to a particular program, and to the language you use to tell this program what to do. When we need to be careful, we call the program "the `awk' utility" and the language "the `awk' language." The term `gawk' refers to a version of `awk' developed as part the GNU project. The purpose of this Info file is to explain both the `awk' language and how to run the `awk' utility. The main purpose of the Info file is to explain the features of `awk', as defined in the POSIX standard. It does so in the context of one particular implementation, `gawk'. While doing so, it will also attempt to describe important differences between `gawk' and other `awk' implementations. Finally, any `gawk' features that are not in the POSIX standard for `awk' will be noted. The term "`awk' program" refers to a program written by you in the `awk' programming language. *Note Getting Started with `awk': Getting Started, for the bare essentials you need to know to start using `awk'. Some useful "one-liners" are included to give you a feel for the `awk' language (*note Useful One Line Programs: One-liners.). Many sample `awk' programs have been provided for you (*note A Library of `awk' Functions: Library Functions.; also *note Practical `awk' Programs: Sample Programs.). The entire `awk' language is summarized for quick reference in *Note `gawk' Summary: Gawk Summary. Look there if you just need to refresh your memory about a particular feature. If you find terms that you aren't familiar with, try looking them up in the glossary (*note Glossary::.). Most of the time complete `awk' programs are used as examples, but in some of the more advanced sections, only the part of the `awk' program that illustrates the concept being described is shown. While this Info file is aimed principally at people who have not been exposed to `awk', there is a lot of information here that even the `awk' expert should find useful. In particular, the description of POSIX `awk', and the example programs in *Note A Library of `awk' Functions: Library Functions, and *Note Practical `awk' Programs: Sample Programs, should be of interest. Dark Corners ------------ Who opened that window shade?!? Count Dracula Until the POSIX standard (and `The Gawk Manual'), many features of `awk' were either poorly documented, or not documented at all. Descriptions of such features (often called "dark corners") are noted in this Info file with "(d.c.)". They also appear in the index under the heading "dark corner."  File: gawk.info, Node: Conventions, Next: Sample Data Files, Prev: This Manual, Up: What Is Awk Typographical Conventions ========================= This Info file is written using Texinfo, the GNU documentation formatting language. A single Texinfo source file is used to produce both the printed and on-line versions of the documentation. This section briefly documents the typographical conventions used in Texinfo. Examples you would type at the command line are preceded by the common shell primary and secondary prompts, `$' and `>'. Output from the command is preceded by the glyph "-|". This typically represents the command's standard output. Error messages, and other output on the command's standard error, are preceded by the glyph "error-->". For example: $ echo hi on stdout -| hi on stdout $ echo hello on stderr 1>&2 error--> hello on stderr Characters that you type at the keyboard look `like this'. In particular, there are special characters called "control characters." These are characters that you type by holding down both the `CONTROL' key and another key, at the same time. For example, a `Control-d' is typed by first pressing and holding the `CONTROL' key, next pressing the `d' key, and finally releasing both keys.  File: gawk.info, Node: Sample Data Files, Prev: Conventions, Up: What Is Awk Data Files for the Examples =========================== Many of the examples in this Info file take their input from two sample data files. The first, called `BBS-list', represents a list of computer bulletin board systems together with information about those systems. The second data file, called `inventory-shipped', contains information about shipments on a monthly basis. In both files, each line is considered to be one "record". In the file `BBS-list', each record contains the name of a computer bulletin board, its phone number, the board's baud rate(s), and a code for the number of hours it is operational. An `A' in the last column means the board operates 24 hours a day. A `B' in the last column means the board operates evening and weekend hours, only. A `C' means the board operates only on weekends. aardvark 555-5553 1200/300 B alpo-net 555-3412 2400/1200/300 A barfly 555-7685 1200/300 A bites 555-1675 2400/1200/300 A camelot 555-0542 300 C core 555-2912 1200/300 C fooey 555-1234 2400/1200/300 B foot 555-6699 1200/300 B macfoo 555-6480 1200/300 A sdace 555-3430 2400/1200/300 A sabafoo 555-2127 1200/300 C The second data file, called `inventory-shipped', represents information about shipments during the year. Each record contains the month of the year, the number of green crates shipped, the number of red boxes shipped, the number of orange bags shipped, and the number of blue packages shipped, respectively. There are 16 entries, covering the 12 months of one year and four months of the next year. Jan 13 25 15 115 Feb 15 32 24 226 Mar 15 24 34 228 Apr 31 52 63 420 May 16 34 29 208 Jun 31 42 75 492 Jul 24 34 67 436 Aug 15 34 47 316 Sep 13 55 37 277 Oct 29 54 68 525 Nov 20 87 82 577 Dec 17 35 61 401 Jan 21 36 64 620 Feb 26 58 80 652 Mar 24 75 70 495 Apr 21 70 74 514 If you are reading this in GNU Emacs using Info, you can copy the regions of text showing these sample files into your own test files. This way you can try out the examples shown in the remainder of this document. You do this by using the command `M-x write-region' to copy text from the Info file into a file for use with `awk' (*Note Miscellaneous File Operations: (emacs)Misc File Ops, for more information). Using this information, create your own `BBS-list' and `inventory-shipped' files, and practice what you learn in this Info file. If you are using the stand-alone version of Info, see *Note Extracting Programs from Texinfo Source Files: Extract Program, for an `awk' program that will extract these data files from `gawk.texi', the Texinfo source file for this Info file.  File: gawk.info, Node: Getting Started, Next: One-liners, Prev: What Is Awk, Up: Top Getting Started with `awk' ************************** The basic function of `awk' is to search files for lines (or other units of text) that contain certain patterns. When a line matches one of the patterns, `awk' performs specified actions on that line. `awk' keeps processing input lines in this way until the end of the input files are reached. Programs in `awk' are different from programs in most other languages, because `awk' programs are "data-driven"; that is, you describe the data you wish to work with, and then what to do when you find it. Most other languages are "procedural"; you have to describe, in great detail, every step the program is to take. When working with procedural languages, it is usually much harder to clearly describe the data your program will process. For this reason, `awk' programs are often refreshingly easy to both write and read. When you run `awk', you specify an `awk' "program" that tells `awk' what to do. The program consists of a series of "rules". (It may also contain "function definitions", an advanced feature which we will ignore for now. *Note User-defined Functions: User-defined.) Each rule specifies one pattern to search for, and one action to perform when that pattern is found. Syntactically, a rule consists of a pattern followed by an action. The action is enclosed in curly braces to separate it from the pattern. Rules are usually separated by newlines. Therefore, an `awk' program looks like this: PATTERN { ACTION } PATTERN { ACTION } ... * Menu: * Names:: What name to use to find `awk'. * Running gawk:: How to run `gawk' programs; includes command line syntax. * Very Simple:: A very simple example. * Two Rules:: A less simple one-line example with two rules. * More Complex:: A more complex example. * Statements/Lines:: Subdividing or combining statements into lines. * Other Features:: Other Features of `awk'. * When:: When to use `gawk' and when to use other things.  File: gawk.info, Node: Names, Next: Running gawk, Prev: Getting Started, Up: Getting Started A Rose By Any Other Name ======================== The `awk' language has evolved over the years. Full details are provided in *Note The Evolution of the `awk' Language: Language History. The language described in this Info file is often referred to as "new `awk'." Because of this, many systems have multiple versions of `awk'. Some systems have an `awk' utility that implements the original version of the `awk' language, and a `nawk' utility for the new version. Others have an `oawk' for the "old `awk'" language, and plain `awk' for the new one. Still others only have one version, usually the new one.(1) All in all, this makes it difficult for you to know which version of `awk' you should run when writing your programs. The best advice we can give here is to check your local documentation. Look for `awk', `oawk', and `nawk', as well as for `gawk'. Chances are, you will have some version of new `awk' on your system, and that is what you should use when running your programs. (Of course, if you're reading this Info file, chances are good that you have `gawk'!) Throughout this Info file, whenever we refer to a language feature that should be available in any complete implementation of POSIX `awk', we simply use the term `awk'. When referring to a feature that is specific to the GNU implementation, we use the term `gawk'. ---------- Footnotes ---------- (1) Often, these systems use `gawk' for their `awk' implementation!  File: gawk.info, Node: Running gawk, Next: Very Simple, Prev: Names, Up: Getting Started How to Run `awk' Programs ========================= There are several ways to run an `awk' program. If the program is short, it is easiest to include it in the command that runs `awk', like this: awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ... where PROGRAM consists of a series of patterns and actions, as described earlier. (The reason for the single quotes is described below, in *Note One-shot Throw-away `awk' Programs: One-shot.) When the program is long, it is usually more convenient to put it in a file and run it with a command like this: awk -f PROGRAM-FILE INPUT-FILE1 INPUT-FILE2 ... * Menu: * One-shot:: Running a short throw-away `awk' program. * Read Terminal:: Using no input files (input from terminal instead). * Long:: Putting permanent `awk' programs in files. * Executable Scripts:: Making self-contained `awk' programs. * Comments:: Adding documentation to `gawk' programs.  File: gawk.info, Node: One-shot, Next: Read Terminal, Prev: Running gawk, Up: Running gawk One-shot Throw-away `awk' Programs ---------------------------------- Once you are familiar with `awk', you will often type in simple programs the moment you want to use them. Then you can write the program as the first argument of the `awk' command, like this: awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ... where PROGRAM consists of a series of PATTERNS and ACTIONS, as described earlier. This command format instructs the "shell", or command interpreter, to start `awk' and use the PROGRAM to process records in the input file(s). There are single quotes around PROGRAM so that the shell doesn't interpret any `awk' characters as special shell characters. They also cause the shell to treat all of PROGRAM as a single argument for `awk' and allow PROGRAM to be more than one line long. This format is also useful for running short or medium-sized `awk' programs from shell scripts, because it avoids the need for a separate file for the `awk' program. A self-contained shell script is more reliable since there are no other files to misplace. *Note Useful One Line Programs: One-liners, presents several short, self-contained programs. As an interesting side point, the command awk '/foo/' FILES ... is essentially the same as egrep foo FILES ...  File: gawk.info, Node: Read Terminal, Next: Long, Prev: One-shot, Up: Running gawk Running `awk' without Input Files --------------------------------- You can also run `awk' without any input files. If you type the command line: awk 'PROGRAM' then `awk' applies the PROGRAM to the "standard input", which usually means whatever you type on the terminal. This continues until you indicate end-of-file by typing `Control-d'. (On other operating systems, the end-of-file character may be different. For example, on OS/2 and MS-DOS, it is `Control-z'.) For example, the following program prints a friendly piece of advice (from Douglas Adams' `The Hitchhiker's Guide to the Galaxy'), to keep you from worrying about the complexities of computer programming (`BEGIN' is a feature we haven't discussed yet). $ awk "BEGIN { print \"Don't Panic!\" }" -| Don't Panic! This program does not read any input. The `\' before each of the inner double quotes is necessary because of the shell's quoting rules, in particular because it mixes both single quotes and double quotes. This next simple `awk' program emulates the `cat' utility; it copies whatever you type at the keyboard to its standard output. (Why this works is explained shortly.) $ awk '{ print }' Now is the time for all good men -| Now is the time for all good men to come to the aid of their country. -| to come to the aid of their country. Four score and seven years ago, ... -| Four score and seven years ago, ... What, me worry? -| What, me worry? Control-d  File: gawk.info, Node: Long, Next: Executable Scripts, Prev: Read Terminal, Up: Running gawk Running Long Programs --------------------- Sometimes your `awk' programs can be very long. In this case it is more convenient to put the program into a separate file. To tell `awk' to use that file for its program, you type: awk -f SOURCE-FILE INPUT-FILE1 INPUT-FILE2 ... The `-f' instructs the `awk' utility to get the `awk' program from the file SOURCE-FILE. Any file name can be used for SOURCE-FILE. For example, you could put the program: BEGIN { print "Don't Panic!" } into the file `advice'. Then this command: awk -f advice does the same thing as this one: awk "BEGIN { print \"Don't Panic!\" }" which was explained earlier (*note Running `awk' without Input Files: Read Terminal.). Note that you don't usually need single quotes around the file name that you specify with `-f', because most file names don't contain any of the shell's special characters. Notice that in `advice', the `awk' program did not have single quotes around it. The quotes are only needed for programs that are provided on the `awk' command line. If you want to identify your `awk' program files clearly as such, you can add the extension `.awk' to the file name. This doesn't affect the execution of the `awk' program, but it does make "housekeeping" easier.  File: gawk.info, Node: Executable Scripts, Next: Comments, Prev: Long, Up: Running gawk Executable `awk' Programs ------------------------- Once you have learned `awk', you may want to write self-contained `awk' scripts, using the `#!' script mechanism. You can do this on many Unix systems(1) (and someday on the GNU system). For example, you could update the file `advice' to look like this: #! /bin/awk -f BEGIN { print "Don't Panic!" } After making this file executable (with the `chmod' utility), you can simply type `advice' at the shell, and the system will arrange to run `awk'(2) as if you had typed `awk -f advice'. $ advice -| Don't Panic! Self-contained `awk' scripts are useful when you want to write a program which users can invoke without their having to know that the program is written in `awk'. Some older systems do not support the `#!' mechanism. You can get a similar effect using a regular shell script. It would look something like this: : The colon ensures execution by the standard shell. awk 'PROGRAM' "$@@" Using this technique, it is *vital* to enclose the PROGRAM in single quotes to protect it from interpretation by the shell. If you omit the quotes, only a shell wizard can predict the results. The `"$@@"' causes the shell to forward all the command line arguments to the `awk' program, without interpretation. The first line, which starts with a colon, is used so that this shell script will work even if invoked by a user who uses the C shell. (Not all older systems obey this convention, but many do.) ---------- Footnotes ---------- (1) The `#!' mechanism works on Linux systems, Unix systems derived from Berkeley Unix, System V Release 4, and some System V Release 3 systems. (2) The line beginning with `#!' lists the full file name of an interpreter to be run, and an optional initial command line argument to pass to that interpreter. The operating system then runs the interpreter with the given argument and the full argument list of the executed program. The first argument in the list is the full file name of the `awk' program. The rest of the argument list will either be options to `awk', or data files, or both.  File: gawk.info, Node: Comments, Prev: Executable Scripts, Up: Running gawk Comments in `awk' Programs -------------------------- A "comment" is some text that is included in a program for the sake of human readers; it is not really part of the program. Comments can explain what the program does, and how it works. Nearly all programming languages have provisions for comments, because programs are typically hard to understand without their extra help. In the `awk' language, a comment starts with the sharp sign character, `#', and continues to the end of the line. The `#' does not have to be the first character on the line. The `awk' language ignores the rest of a line following a sharp sign. For example, we could have put the following into `advice': # This program prints a nice friendly message. It helps # keep novice users from being afraid of the computer. BEGIN { print "Don't Panic!" } You can put comment lines into keyboard-composed throw-away `awk' programs also, but this usually isn't very useful; the purpose of a comment is to help you or another person understand the program at a later time.  File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Running gawk, Up: Getting Started A Very Simple Example ===================== The following command runs a simple `awk' program that searches the input file `BBS-list' for the string of characters: `foo'. (A string of characters is usually called a "string". The term "string" is perhaps based on similar usage in English, such as "a string of pearls," or, "a string of cars in a train.") awk '/foo/ { print $0 }' BBS-list When lines containing `foo' are found, they are printed, because `print $0' means print the current line. (Just `print' by itself means the same thing, so we could have written that instead.) You will notice that slashes, `/', surround the string `foo' in the `awk' program. The slashes indicate that `foo' is a pattern to search for. This type of pattern is called a "regular expression", and is covered in more detail later (*note Regular Expressions: Regexp.). The pattern is allowed to match parts of words. There are single-quotes around the `awk' program so that the shell won't interpret any of it as special shell characters. Here is what this program prints: $ awk '/foo/ { print $0 }' BBS-list -| fooey 555-1234 2400/1200/300 B -| foot 555-6699 1200/300 B -| macfoo 555-6480 1200/300 A -| sabafoo 555-2127 1200/300 C In an `awk' rule, either the pattern or the action can be omitted, but not both. If the pattern is omitted, then the action is performed for *every* input line. If the action is omitted, the default action is to print all lines that match the pattern. Thus, we could leave out the action (the `print' statement and the curly braces) in the above example, and the result would be the same: all lines matching the pattern `foo' would be printed. By comparison, omitting the `print' statement but retaining the curly braces makes an empty action that does nothing; then no lines would be printed.  File: gawk.info, Node: Two Rules, Next: More Complex, Prev: Very Simple, Up: Getting Started An Example with Two Rules ========================= The `awk' utility reads the input files one line at a time. For each line, `awk' tries the patterns of each of the rules. If several patterns match then several actions are run, in the order in which they appear in the `awk' program. If no patterns match, then no actions are run. After processing all the rules (perhaps none) that match the line, `awk' reads the next line (however, *note The `next' Statement: Next Statement., and also *note The `nextfile' Statement: Nextfile Statement.). This continues until the end of the file is reached. For example, the `awk' program: /12/ { print $0 } /21/ { print $0 } contains two rules. The first rule has the string `12' as the pattern and `print $0' as the action. The second rule has the string `21' as the pattern and also has `print $0' as the action. Each rule's action is enclosed in its own pair of braces. This `awk' program prints every line that contains the string `12' *or* the string `21'. If a line contains both strings, it is printed twice, once by each rule. This is what happens if we run this program on our two sample data files, `BBS-list' and `inventory-shipped', as shown here: $ awk '/12/ { print $0 } > /21/ { print $0 }' BBS-list inventory-shipped -| aardvark 555-5553 1200/300 B -| alpo-net 555-3412 2400/1200/300 A -| barfly 555-7685 1200/300 A -| bites 555-1675 2400/1200/300 A -| core 555-2912 1200/300 C -| fooey 555-1234 2400/1200/300 B -| foot 555-6699 1200/300 B -| macfoo 555-6480 1200/300 A -| sdace 555-3430 2400/1200/300 A -| sabafoo 555-2127 1200/300 C -| sabafoo 555-2127 1200/300 C -| Jan 21 36 64 620 -| Apr 21 70 74 514 Note how the line in `BBS-list' beginning with `sabafoo' was printed twice, once for each rule.  File: gawk.info, Node: More Complex, Next: Statements/Lines, Prev: Two Rules, Up: Getting Started A More Complex Example ====================== Here is an example to give you an idea of what typical `awk' programs do. This example shows how `awk' can be used to summarize, select, and rearrange the output of another utility. It uses features that haven't been covered yet, so don't worry if you don't understand all the details. ls -lg | awk '$6 == "Nov" { sum += $5 } END { print sum }' This command prints the total number of bytes in all the files in the current directory that were last modified in November (of any year). (In the C shell you would need to type a semicolon and then a backslash at the end of the first line; in a POSIX-compliant shell, such as the Bourne shell or Bash, the GNU Bourne-Again shell, you can type the example as shown.) The `ls -lg' part of this example is a system command that gives you a listing of the files in a directory, including file size and the date the file was last modified. Its output looks like this: -rw-r--r-- 1 arnold user 1933 Nov 7 13:05 Makefile -rw-r--r-- 1 arnold user 10809 Nov 7 13:03 gawk.h -rw-r--r-- 1 arnold user 983 Apr 13 12:14 gawk.tab.h -rw-r--r-- 1 arnold user 31869 Jun 15 12:20 gawk.y -rw-r--r-- 1 arnold user 22414 Nov 7 13:03 gawk1.c -rw-r--r-- 1 arnold user 37455 Nov 7 13:03 gawk2.c -rw-r--r-- 1 arnold user 27511 Dec 9 13:07 gawk3.c -rw-r--r-- 1 arnold user 7989 Nov 7 13:03 gawk4.c The first field contains read-write permissions, the second field contains the number of links to the file, and the third field identifies the owner of the file. The fourth field identifies the group of the file. The fifth field contains the size of the file in bytes. The sixth, seventh and eighth fields contain the month, day, and time, respectively, that the file was last modified. Finally, the ninth field contains the name of the file. The `$6 == "Nov"' in our `awk' program is an expression that tests whether the sixth field of the output from `ls -lg' matches the string `Nov'. Each time a line has the string `Nov' for its sixth field, the action `sum += $5' is performed. This adds the fifth field (the file size) to the variable `sum'. As a result, when `awk' has finished reading all the input lines, `sum' is the sum of the sizes of files whose lines matched the pattern. (This works because `awk' variables are automatically initialized to zero.) After the last line of output from `ls' has been processed, the `END' rule is executed, and the value of `sum' is printed. In this example, the value of `sum' would be 80600. These more advanced `awk' techniques are covered in later sections (*note Overview of Actions: Action Overview.). Before you can move on to more advanced `awk' programming, you have to know how `awk' interprets your input and displays your output. By manipulating fields and using `print' statements, you can produce some very useful and impressive looking reports.  File: gawk.info, Node: Statements/Lines, Next: Other Features, Prev: More Complex, Up: Getting Started `awk' Statements Versus Lines ============================= Most often, each line in an `awk' program is a separate statement or separate rule, like this: awk '/12/ { print $0 } /21/ { print $0 }' BBS-list inventory-shipped However, `gawk' will ignore newlines after any of the following: , { ? : || && do else A newline at any other point is considered the end of the statement. (Splitting lines after `?' and `:' is a minor `gawk' extension. The `?' and `:' referred to here is the three operand conditional expression described in *Note Conditional Expressions: Conditional Exp.) If you would like to split a single statement into two lines at a point where a newline would terminate it, you can "continue" it by ending the first line with a backslash character, `\'. The backslash must be the final character on the line to be recognized as a continuation character. This is allowed absolutely anywhere in the statement, even in the middle of a string or regular expression. For example: awk '/This regular expression is too long, so continue it\ on the next line/ { print $1 }' We have generally not used backslash continuation in the sample programs in this Info file. Since in `gawk' there is no limit on the length of a line, it is never strictly necessary; it just makes programs more readable. For this same reason, as well as for clarity, we have kept most statements short in the sample programs presented throughout the Info file. Backslash continuation is most useful when your `awk' program is in a separate source file, instead of typed in on the command line. You should also note that many `awk' implementations are more particular about where you may use backslash continuation. For example, they may not allow you to split a string constant using backslash continuation. Thus, for maximal portability of your `awk' programs, it is best not to split your lines in the middle of a regular expression or a string. *Caution: backslash continuation does not work as described above with the C shell.* Continuation with backslash works for `awk' programs in files, and also for one-shot programs *provided* you are using a POSIX-compliant shell, such as the Bourne shell or Bash, the GNU Bourne-Again shell. But the C shell (`csh') behaves differently! There, you must use two backslashes in a row, followed by a newline. Note also that when using the C shell, *every* newline in your awk program must be escaped with a backslash. To illustrate: % awk 'BEGIN { \ ? print \\ ? "hello, world" \ ? }' -| hello, world Here, the `%' and `?' are the C shell's primary and secondary prompts, analogous to the standard shell's `$' and `>'. `awk' is a line-oriented language. Each rule's action has to begin on the same line as the pattern. To have the pattern and action on separate lines, you *must* use backslash continuation--there is no other way. Note that backslash continuation and comments do not mix. As soon as `awk' sees the `#' that starts a comment, it ignores *everything* on the rest of the line. For example: $ gawk 'BEGIN { print "dont panic" # a friendly \ > BEGIN rule > }' error--> gawk: cmd. line:2: BEGIN rule error--> gawk: cmd. line:2: ^ parse error Here, it looks like the backslash would continue the comment onto the next line. However, the backslash-newline combination is never even noticed, since it is "hidden" inside the comment. Thus, the `BEGIN' is noted as a syntax error. When `awk' statements within one rule are short, you might want to put more than one of them on a line. You do this by separating the statements with a semicolon, `;'. This also applies to the rules themselves. Thus, the previous program could have been written: /12/ { print $0 } ; /21/ { print $0 } *Note:* the requirement that rules on the same line must be separated with a semicolon was not in the original `awk' language; it was added for consistency with the treatment of statements within an action.  File: gawk.info, Node: Other Features, Next: When, Prev: Statements/Lines, Up: Getting Started Other Features of `awk' ======================= The `awk' language provides a number of predefined, or built-in variables, which your programs can use to get information from `awk'. There are other variables your program can set to control how `awk' processes your data. In addition, `awk' provides a number of built-in functions for doing common computational and string related operations. As we develop our presentation of the `awk' language, we introduce most of the variables and many of the functions. They are defined systematically in *Note Built-in Variables::, and *Note Built-in Functions: Built-in.  File: gawk.info, Node: When, Prev: Other Features, Up: Getting Started When to Use `awk' ================= You might wonder how `awk' might be useful for you. Using utility programs, advanced patterns, field separators, arithmetic statements, and other selection criteria, you can produce much more complex output. The `awk' language is very useful for producing reports from large amounts of raw data, such as summarizing information from the output of other utility programs like `ls'. (*Note A More Complex Example: More Complex.) Programs written with `awk' are usually much smaller than they would be in other languages. This makes `awk' programs easy to compose and use. Often, `awk' programs can be quickly composed at your terminal, used once, and thrown away. Since `awk' programs are interpreted, you can avoid the (usually lengthy) compilation part of the typical edit-compile-test-debug cycle of software development. Complex programs have been written in `awk', including a complete retargetable assembler for eight-bit microprocessors (*note Glossary::., for more information) and a microcode assembler for a special purpose Prolog computer. However, `awk''s capabilities are strained by tasks of such complexity. If you find yourself writing `awk' scripts of more than, say, a few hundred lines, you might consider using a different programming language. Emacs Lisp is a good choice if you need sophisticated string or pattern matching capabilities. The shell is also good at string and pattern matching; in addition, it allows powerful use of the system utilities. More conventional languages, such as C, C++, and Lisp, offer better facilities for system programming and for managing the complexity of large programs. Programs in these languages may require more lines of source code than the equivalent `awk' programs, but they are easier to maintain and usually run more efficiently.  File: gawk.info, Node: One-liners, Next: Regexp, Prev: Getting Started, Up: Top Useful One Line Programs ************************ Many useful `awk' programs are short, just a line or two. Here is a collection of useful, short programs to get you started. Some of these programs contain constructs that haven't been covered yet. The description of the program will give you a good idea of what is going on, but please read the rest of the Info file to become an `awk' expert! Most of the examples use a data file named `data'. This is just a placeholder; if you were to use these programs yourself, you would substitute your own file names for `data'. Since you are reading this in Info, each line of the example code is enclosed in quotes, to represent text that you would type literally. The examples themselves represent shell commands that use single quotes to keep the shell from interpreting the contents of the program. When reading the examples, focus on the text between the open and close quotes. `awk '{ if (length($0) > max) max = length($0) }' ` END { print max }' data' This program prints the length of the longest input line. `awk 'length($0) > 80' data' This program prints every line that is longer than 80 characters. The sole rule has a relational expression as its pattern, and has no action (so the default action, printing the record, is used). `expand data | awk '{ if (x < length()) x = length() }' ` END { print "maximum line length is " x }'' This program prints the length of the longest line in `data'. The input is processed by the `expand' program to change tabs into spaces, so the widths compared are actually the right-margin columns. `awk 'NF > 0' data' This program prints every line that has at least one field. This is an easy way to delete blank lines from a file (or rather, to create a new file similar to the old file but from which the blank lines have been deleted). `awk 'BEGIN { for (i = 1; i <= 7; i++)' ` print int(101 * rand()) }'' This program prints seven random numbers from zero to 100, inclusive. `ls -lg FILES | awk '{ x += $5 } ; END { print "total bytes: " x }'' This program prints the total number of bytes used by FILES. `ls -lg FILES | awk '{ x += $5 }' ` END { print "total K-bytes: " (x + 1023)/1024 }'' This program prints the total number of kilobytes used by FILES. `awk -F: '{ print $1 }' /etc/passwd | sort' This program prints a sorted list of the login names of all users. `awk 'END { print NR }' data' This program counts lines in a file. `awk 'NR % 2 == 0' data' This program prints the even numbered lines in the data file. If you were to use the expression `NR % 2 == 1' instead, it would print the odd numbered lines.  File: gawk.info, Node: Regexp, Next: Reading Files, Prev: One-liners, Up: Top Regular Expressions ******************* A "regular expression", or "regexp", is a way of describing a set of strings. Because regular expressions are such a fundamental part of `awk' programming, their format and use deserve a separate chapter. A regular expression enclosed in slashes (`/') is an `awk' pattern that matches every input record whose text belongs to that set. The simplest regular expression is a sequence of letters, numbers, or both. Such a regexp matches any string that contains that sequence. Thus, the regexp `foo' matches any string containing `foo'. Therefore, the pattern `/foo/' matches any input record containing the three characters `foo', *anywhere* in the record. Other kinds of regexps let you specify more complicated classes of strings. * Menu: * Regexp Usage:: How to Use Regular Expressions. * Escape Sequences:: How to write non-printing characters. * Regexp Operators:: Regular Expression Operators. * GNU Regexp Operators:: Operators specific to GNU software. * Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps.  File: gawk.info, Node: Regexp Usage, Next: Escape Sequences, Prev: Regexp, Up: Regexp How to Use Regular Expressions ============================== A regular expression can be used as a pattern by enclosing it in slashes. Then the regular expression is tested against the entire text of each record. (Normally, it only needs to match some part of the text in order to succeed.) For example, this prints the second field of each record that contains the three characters `foo' anywhere in it: $ awk '/foo/ { print $2 }' BBS-list -| 555-1234 -| 555-6699 -| 555-6480 -| 555-2127 Regular expressions can also be used in matching expressions. These expressions allow you to specify the string to match against; it need not be the entire current input record. The two operators, `~' and `!~', perform regular expression comparisons. Expressions using these operators can be used as patterns or in `if', `while', `for', and `do' statements. (*Note Control Statements in Actions: Statements.) `EXP ~ /REGEXP/' This is true if the expression EXP (taken as a string) is matched by REGEXP. The following example matches, or selects, all input records with the upper-case letter `J' somewhere in the first field: $ awk '$1 ~ /J/' inventory-shipped -| Jan 13 25 15 115 -| Jun 31 42 75 492 -| Jul 24 34 67 436 -| Jan 21 36 64 620 So does this: awk '{ if ($1 ~ /J/) print }' inventory-shipped `EXP !~ /REGEXP/' This is true if the expression EXP (taken as a character string) is *not* matched by REGEXP. The following example matches, or selects, all input records whose first field *does not* contain the upper-case letter `J': $ awk '$1 !~ /J/' inventory-shipped -| Feb 15 32 24 226 -| Mar 15 24 34 228 -| Apr 31 52 63 420 -| May 16 34 29 208 ... When a regexp is written enclosed in slashes, like `/foo/', we call it a "regexp constant", much like `5.27' is a numeric constant, and `"foo"' is a string constant.  File: gawk.info, Node: Escape Sequences, Next: Regexp Operators, Prev: Regexp Usage, Up: Regexp Escape Sequences ================ Some characters cannot be included literally in string constants (`"foo"') or regexp constants (`/foo/'). You represent them instead with "escape sequences", which are character sequences beginning with a backslash (`\'). One use of an escape sequence is to include a double-quote character in a string constant. Since a plain double-quote would end the string, you must use `\"' to represent an actual double-quote character as a part of the string. For example: $ awk 'BEGIN { print "He said \"hi!\" to her." }' -| He said "hi!" to her. The backslash character itself is another character that cannot be included normally; you write `\\' to put one backslash in the string or regexp. Thus, the string whose contents are the two characters `"' and `\' must be written `"\"\\"'. Another use of backslash is to represent unprintable characters such as tab or newline. While there is nothing to stop you from entering most unprintable characters directly in a string constant or regexp constant, they may look ugly. Here is a table of all the escape sequences used in `awk', and what they represent. Unless noted otherwise, all of these escape sequences apply to both string constants and regexp constants. `\\' A literal backslash, `\'. `\a' The "alert" character, `Control-g', ASCII code 7 (BEL). `\b' Backspace, `Control-h', ASCII code 8 (BS). `\f' Formfeed, `Control-l', ASCII code 12 (FF). `\n' Newline, `Control-j', ASCII code 10 (LF). `\r' Carriage return, `Control-m', ASCII code 13 (CR). `\t' Horizontal tab, `Control-i', ASCII code 9 (HT). `\v' Vertical tab, `Control-k', ASCII code 11 (VT). `\NNN' The octal value NNN, where NNN are one to three digits between `0' and `7'. For example, the code for the ASCII ESC (escape) character is `\033'. `\xHH...' The hexadecimal value HH, where HH are hexadecimal digits (`0' through `9' and either `A' through `F' or `a' through `f'). Like the same construct in ANSI C, the escape sequence continues until the first non-hexadecimal digit is seen. However, using more than two hexadecimal digits produces undefined results. (The `\x' escape sequence is not allowed in POSIX `awk'.) `\/' A literal slash (necessary for regexp constants only). You use this when you wish to write a regexp constant that contains a slash. Since the regexp is delimited by slashes, you need to escape the slash that is part of the pattern, in order to tell `awk' to keep processing the rest of the regexp. `\"' A literal double-quote (necessary for string constants only). You use this when you wish to write a string constant that contains a double-quote. Since the string is delimited by double-quotes, you need to escape the quote that is part of the string, in order to tell `awk' to keep processing the rest of the string. In `gawk', there are additional two character sequences that begin with backslash that have special meaning in regexps. *Note Additional Regexp Operators Only in `gawk': GNU Regexp Operators. In a string constant, what happens if you place a backslash before something that is not one of the characters listed above? POSIX `awk' purposely leaves this case undefined. There are two choices. * Strip the backslash out. This is what Unix `awk' and `gawk' both do. For example, `"a\qc"' is the same as `"aqc"'. * Leave the backslash alone. Some other `awk' implementations do this. In such implementations, `"a\qc"' is the same as if you had typed `"a\\qc"'. In a regexp, a backslash before any character that is not in the above table, and not listed in *Note Additional Regexp Operators Only in `gawk': GNU Regexp Operators, means that the next character should be taken literally, even if it would normally be a regexp operator. E.g., `/a\+b/' matches the three characters `a+b'. For complete portability, do not use a backslash before any character not listed in the table above. Another interesting question arises. Suppose you use an octal or hexadecimal escape to represent a regexp metacharacter (*note Regular Expression Operators: Regexp Operators.). Does `awk' treat the character as literal character, or as a regexp operator? It turns out that historically, such characters were taken literally (d.c.). However, the POSIX standard indicates that they should be treated as real metacharacters, and this is what `gawk' does. However, in compatibility mode (*note Command Line Options: Options.), `gawk' treats the characters represented by octal and hexadecimal escape sequences literally when used in regexp constants. Thus, `/a\52b/' is equivalent to `/a\*b/'. To summarize: 1. The escape sequences in the table above are always processed first, for both string constants and regexp constants. This happens very early, as soon as `awk' reads your program. 2. `gawk' processes both regexp constants and dynamic regexps (*note Using Dynamic Regexps: Computed Regexps.), for the special operators listed in *Note Additional Regexp Operators Only in `gawk': GNU Regexp Operators. 3. A backslash before any other character means to treat that character literally.  File: gawk.info, Node: Regexp Operators, Next: GNU Regexp Operators, Prev: Escape Sequences, Up: Regexp Regular Expression Operators ============================ You can combine regular expressions with the following characters, called "regular expression operators", or "metacharacters", to increase the power and versatility of regular expressions. The escape sequences described in *Note Escape Sequences::, are valid inside a regexp. They are introduced by a `\'. They are recognized and converted into the corresponding real characters as the very first step in processing regexps. Here is a table of metacharacters. All characters that are not escape sequences and that are not listed in the table stand for themselves. `\' This is used to suppress the special meaning of a character when matching. For example: \$ matches the character `$'. `^' This matches the beginning of a string. For example: ^@@chapter matches the `@@chapter' at the beginning of a string, and can be used to identify chapter beginnings in Texinfo source files. The `^' is known as an "anchor", since it anchors the pattern to matching only at the beginning of the string. It is important to realize that `^' does not match the beginning of a line embedded in a string. In this example the condition is not true: if ("line1\nLINE 2" ~ /^L/) ... `$' This is similar to `^', but it matches only at the end of a string. For example: p$ matches a record that ends with a `p'. The `$' is also an anchor, and also does not match the end of a line embedded in a string. In this example the condition is not true: if ("line1\nLINE 2" ~ /1$/) ... `.' The period, or dot, matches any single character, *including* the newline character. For example: .P matches any single character followed by a `P' in a string. Using concatenation we can make a regular expression like `U.A', which matches any three-character sequence that begins with `U' and ends with `A'. In strict POSIX mode (*note Command Line Options: Options.), `.' does not match the NUL character, which is a character with all bits equal to zero. Otherwise, NUL is just another character. Other versions of `awk' may not be able to match the NUL character. `[...]' This is called a "character list". It matches any *one* of the characters that are enclosed in the square brackets. For example: [MVX] matches any one of the characters `M', `V', or `X' in a string. Ranges of characters are indicated by using a hyphen between the beginning and ending characters, and enclosing the whole thing in brackets. For example: [0-9] matches any digit. Multiple ranges are allowed. E.g., the list `[A-Za-z0-9]' is a common way to express the idea of "all alphanumeric characters." To include one of the characters `\', `]', `-' or `^' in a character list, put a `\' in front of it. For example: [d\]] matches either `d', or `]'. This treatment of `\' in character lists is compatible with other `awk' implementations, and is also mandated by POSIX. The regular expressions in `awk' are a superset of the POSIX specification for Extended Regular Expressions (EREs). POSIX EREs are based on the regular expressions accepted by the traditional `egrep' utility. "Character classes" are a new feature introduced in the POSIX standard. A character class is a special notation for describing lists of characters that have a specific attribute, but where the actual characters themselves can vary from country to country and/or from character set to character set. For example, the notion of what is an alphabetic character differs in the USA and in France. A character class is only valid in a regexp *inside* the brackets of a character list. Character classes consist of `[:', a keyword denoting the class, and `:]'. Here are the character classes defined by the POSIX standard. `[:alnum:]' Alphanumeric characters. `[:alpha:]' Alphabetic characters. `[:blank:]' Space and tab characters. `[:cntrl:]' Control characters. `[:digit:]' Numeric characters. `[:graph:]' Characters that are printable and are also visible. (A space is printable, but not visible, while an `a' is both.) `[:lower:]' Lower-case alphabetic characters. `[:print:]' Printable characters (characters that are not control characters.) `[:punct:]' Punctuation characters (characters that are not letter, digits, control characters, or space characters). `[:space:]' Space characters (such as space, tab, and formfeed, to name a few). `[:upper:]' Upper-case alphabetic characters. `[:xdigit:]' Characters that are hexadecimal digits. For example, before the POSIX standard, to match alphanumeric characters, you had to write `/[A-Za-z0-9]/'. If your character set had other alphabetic characters in it, this would not match them. With the POSIX character classes, you can write `/[[:alnum:]]/', and this will match *all* the alphabetic and numeric characters in your character set. Two additional special sequences can appear in character lists. These apply to non-ASCII character sets, which can have single symbols (called "collating elements") that are represented with more than one character, as well as several characters that are equivalent for "collating", or sorting, purposes. (E.g., in French, a plain "e" and a grave-accented "`e" are equivalent.) Collating Symbols A "collating symbol" is a multi-character collating element enclosed in `[.' and `.]'. For example, if `ch' is a collating element, then `[[.ch.]]' is a regexp that matches this collating element, while `[ch]' is a regexp that matches either `c' or `h'. Equivalence Classes An "equivalence class" is a locale-specific name for a list of characters that are equivalent. The name is enclosed in `[=' and `=]'. For example, the name `e' might be used to represent all of "e," "`e," and "'e." In this case, `[[=e]]' is a regexp that matches any of `e', `'e', or ``e'. These features are very valuable in non-English speaking locales. *Caution:* The library functions that `gawk' uses for regular expression matching currently only recognize POSIX character classes; they do not recognize collating symbols or equivalence classes. `[^ ...]' This is a "complemented character list". The first character after the `[' *must* be a `^'. It matches any characters *except* those in the square brackets. For example: [^0-9] matches any character that is not a digit. `|' This is the "alternation operator", and it is used to specify alternatives. For example: ^P|[0-9] matches any string that matches either `^P' or `[0-9]'. This means it matches any string that starts with `P' or contains a digit. The alternation applies to the largest possible regexps on either side. In other words, `|' has the lowest precedence of all the regular expression operators. `(...)' Parentheses are used for grouping in regular expressions as in arithmetic. They can be used to concatenate regular expressions containing the alternation operator, `|'. For example, `@@(samp|code)\{[^}]+\}' matches both `@@code{foo}' and `@@samp{bar}'. (These are Texinfo formatting control sequences.) `*' This symbol means that the preceding regular expression is to be repeated as many times as necessary to find a match. For example: ph* applies the `*' symbol to the preceding `h' and looks for matches of one `p' followed by any number of `h's. This will also match just `p' if no `h's are present. The `*' repeats the *smallest* possible preceding expression. (Use parentheses if you wish to repeat a larger expression.) It finds as many repetitions as possible. For example: awk '/\(c[ad][ad]*r x\)/ { print }' sample prints every record in `sample' containing a string of the form `(car x)', `(cdr x)', `(cadr x)', and so on. Notice the escaping of the parentheses by preceding them with backslashes. `+' This symbol is similar to `*', but the preceding expression must be matched at least once. This means that: wh+y would match `why' and `whhy' but not `wy', whereas `wh*y' would match all three of these strings. This is a simpler way of writing the last `*' example: awk '/\(c[ad]+r x\)/ { print }' sample `?' This symbol is similar to `*', but the preceding expression can be matched either once or not at all. For example: fe?d will match `fed' and `fd', but nothing else. `{N}' `{N,}' `{N,M}' One or two numbers inside braces denote an "interval expression". If there is one number in the braces, the preceding regexp is repeated N times. If there are two numbers separated by a comma, the preceding regexp is repeated N to M times. If there is one number followed by a comma, then the preceding regexp is repeated at least N times. `wh{3}y' matches `whhhy' but not `why' or `whhhhy'. `wh{3,5}y' matches `whhhy' or `whhhhy' or `whhhhhy', only. `wh{2,}y' matches `whhy' or `whhhy', and so on. Interval expressions were not traditionally available in `awk'. As part of the POSIX standard they were added, to make `awk' and `egrep' consistent with each other. However, since old programs may use `{' and `}' in regexp constants, by default `gawk' does *not* match interval expressions in regexps. If either `--posix' or `--re-interval' are specified (*note Command Line Options: Options.), then interval expressions are allowed in regexps. In regular expressions, the `*', `+', and `?' operators, as well as the braces `{' and `}', have the highest precedence, followed by concatenation, and finally by `|'. As in arithmetic, parentheses can change how operators are grouped. If `gawk' is in compatibility mode (*note Command Line Options: Options.), character classes and interval expressions are not available in regular expressions. The next node discusses the GNU-specific regexp operators, and provides more detail concerning how command line options affect the way `gawk' interprets the characters in regular expressions.  File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Regexp Operators, Up: Regexp Additional Regexp Operators Only in `gawk' ========================================== GNU software that deals with regular expressions provides a number of additional regexp operators. These operators are described in this section, and are specific to `gawk'; they are not available in other `awk' implementations. Most of the additional operators are for dealing with word matching. For our purposes, a "word" is a sequence of one or more letters, digits, or underscores (`_'). `\w' This operator matches any word-constituent character, i.e. any letter, digit, or underscore. Think of it as a short-hand for `[[:alnum:]_]'. `\W' This operator matches any character that is not word-constituent. Think of it as a short-hand for `[^[:alnum:]_]'. `\<' This operator matches the empty string at the beginning of a word. For example, `/\' This operator matches the empty string at the end of a word. For example, `/stow\>/' matches `stow', but not `stowaway'. `\y' This operator matches the empty string at either the beginning or the end of a word (the word boundar*y*). For example, `\yballs?\y' matches either `ball' or `balls' as a separate word. `\B' This operator matches the empty string within a word. In other words, `\B' matches the empty string that occurs between two word-constituent characters. For example, `/\Brat\B/' matches `crate', but it does not match `dirty rat'. `\B' is essentially the opposite of `\y'. There are two other operators that work on buffers. In Emacs, a "buffer" is, naturally, an Emacs buffer. For other programs, the regexp library routines that `gawk' uses consider the entire string to be matched as the buffer. For `awk', since `^' and `$' always work in terms of the beginning and end of strings, these operators don't add any new capabilities. They are provided for compatibility with other GNU software. `\`' This operator matches the empty string at the beginning of the buffer. `\'' This operator matches the empty string at the end of the buffer. In other GNU software, the word boundary operator is `\b'. However, that conflicts with the `awk' language's definition of `\b' as backspace, so `gawk' uses a different letter. An alternative method would have been to require two backslashes in the GNU operators, but this was deemed to be too confusing, and the current method of using `\y' for the GNU `\b' appears to be the lesser of two evils. The various command line options (*note Command Line Options: Options.) control how `gawk' interprets characters in regexps. No options In the default case, `gawk' provide all the facilities of POSIX regexps and the GNU regexp operators described in *Note Regular Expression Operators: Regexp Operators. However, interval expressions are not supported. `--posix' Only POSIX regexps are supported, the GNU operators are not special (e.g., `\w' matches a literal `w'). Interval expressions are allowed. `--traditional' Traditional Unix `awk' regexps are matched. The GNU operators are not special, interval expressions are not available, and neither are the POSIX character classes (`[[:alnum:]]' and so on). Characters described by octal and hexadecimal escape sequences are treated literally, even if they represent regexp metacharacters. `--re-interval' Allow interval expressions in regexps, even if `--traditional' has been provided.  File: gawk.info, Node: Case-sensitivity, Next: Leftmost Longest, Prev: GNU Regexp Operators, Up: Regexp Case-sensitivity in Matching ============================ Case is normally significant in regular expressions, both when matching ordinary characters (i.e. not metacharacters), and inside character sets. Thus a `w' in a regular expression matches only a lower-case `w' and not an upper-case `W'. The simplest way to do a case-independent match is to use a character list: `[Ww]'. However, this can be cumbersome if you need to use it often; and it can make the regular expressions harder to read. There are two alternatives that you might prefer. One way to do a case-insensitive match at a particular point in the program is to convert the data to a single case, using the `tolower' or `toupper' built-in string functions (which we haven't discussed yet; *note Built-in Functions for String Manipulation: String Functions.). For example: tolower($1) ~ /foo/ { ... } converts the first field to lower-case before matching against it. This will work in any POSIX-compliant implementation of `awk'. Another method, specific to `gawk', is to set the variable `IGNORECASE' to a non-zero value (*note Built-in Variables::.). When `IGNORECASE' is not zero, *all* regexp and string operations ignore case. Changing the value of `IGNORECASE' dynamically controls the case sensitivity of your program as it runs. Case is significant by default because `IGNORECASE' (like most variables) is initialized to zero. x = "aB" if (x ~ /ab/) ... # this test will fail IGNORECASE = 1 if (x ~ /ab/) ... # now it will succeed In general, you cannot use `IGNORECASE' to make certain rules case-insensitive and other rules case-sensitive, because there is no way to set `IGNORECASE' just for the pattern of a particular rule. To do this, you must use character lists or `tolower'. However, one thing you can do only with `IGNORECASE' is turn case-sensitivity on or off dynamically for all the rules at once. `IGNORECASE' can be set on the command line, or in a `BEGIN' rule (*note Other Command Line Arguments: Other Arguments.; also *note Startup and Cleanup Actions: Using BEGIN/END.). Setting `IGNORECASE' from the command line is a way to make a program case-insensitive without having to edit it. Prior to version 3.0 of `gawk', the value of `IGNORECASE' only affected regexp operations. It did not affect string comparison with `==', `!=', and so on. Beginning with version 3.0, both regexp and string comparison operations are affected by `IGNORECASE'. Beginning with version 3.0 of `gawk', the equivalences between upper-case and lower-case characters are based on the ISO-8859-1 (ISO Latin-1) character set. This character set is a superset of the traditional 128 ASCII characters, that also provides a number of characters suitable for use with European languages. The value of `IGNORECASE' has no effect if `gawk' is in compatibility mode (*note Command Line Options: Options.). Case is always significant in compatibility mode.  File: gawk.info, Node: Leftmost Longest, Next: Computed Regexps, Prev: Case-sensitivity, Up: Regexp How Much Text Matches? ====================== Consider the following example: echo aaaabcd | awk '{ sub(/a+/, ""); print }' This example uses the `sub' function (which we haven't discussed yet, *note Built-in Functions for String Manipulation: String Functions.) to make a change to the input record. Here, the regexp `/a+/' indicates "one or more `a' characters," and the replacement text is `'. The input contains four `a' characters. What will the output be? In other words, how many is "one or more"--will `awk' match two, three, or all four `a' characters? The answer is, `awk' (and POSIX) regular expressions always match the leftmost, *longest* sequence of input characters that can match. Thus, in this example, all four `a' characters are replaced with `'. $ echo aaaabcd | awk '{ sub(/a+/, ""); print }' -| bcd For simple match/no-match tests, this is not so important. But when doing regexp-based field and record splitting, and text matching and substitutions with the `match', `sub', `gsub', and `gensub' functions, it is very important. *Note Built-in Functions for String Manipulation: String Functions, for more information on these functions. Understanding this principle is also important for regexp-based record and field splitting (*note How Input is Split into Records: Records., and also *note Specifying How Fields are Separated: Field Separators.).  File: gawk.info, Node: Computed Regexps, Prev: Leftmost Longest, Up: Regexp Using Dynamic Regexps ===================== The right hand side of a `~' or `!~' operator need not be a regexp constant (i.e. a string of characters between slashes). It may be any expression. The expression is evaluated, and converted if necessary to a string; the contents of the string are used as the regexp. A regexp that is computed in this way is called a "dynamic regexp". For example: BEGIN { identifier_regexp = "[A-Za-z_][A-Za-z_0-9]+" } $0 ~ identifier_regexp { print } sets `identifier_regexp' to a regexp that describes `awk' variable names, and tests if the input record matches this regexp. *Caution:* When using the `~' and `!~' operators, there is a difference between a regexp constant enclosed in slashes, and a string constant enclosed in double quotes. If you are going to use a string constant, you have to understand that the string is in essence scanned *twice*; the first time when `awk' reads your program, and the second time when it goes to match the string on the left-hand side of the operator with the pattern on the right. This is true of any string valued expression (such as `identifier_regexp' above), not just string constants. What difference does it make if the string is scanned twice? The answer has to do with escape sequences, and particularly with backslashes. To get a backslash into a regular expression inside a string, you have to type two backslashes. For example, `/\*/' is a regexp constant for a literal `*'. Only one backslash is needed. To do the same thing with a string, you would have to type `"\\*"'. The first backslash escapes the second one, so that the string actually contains the two characters `\' and `*'. Given that you can use both regexp and string constants to describe regular expressions, which should you use? The answer is "regexp constants," for several reasons. 1. String constants are more complicated to write, and more difficult to read. Using regexp constants makes your programs less error-prone. Not understanding the difference between the two kinds of constants is a common source of errors. 2. It is also more efficient to use regexp constants: `awk' can note that you have supplied a regexp and store it internally in a form that makes pattern matching more efficient. When using a string constant, `awk' must first convert the string into this internal form, and then perform the pattern matching. 3. Using regexp constants is better style; it shows clearly that you intend a regexp match.  File: gawk.info, Node: Reading Files, Next: Printing, Prev: Regexp, Up: Top Reading Input Files ******************* In the typical `awk' program, all input is read either from the standard input (by default the keyboard, but often a pipe from another command) or from files whose names you specify on the `awk' command line. If you specify input files, `awk' reads them in order, reading all the data from one before going on to the next. The name of the current input file can be found in the built-in variable `FILENAME' (*note Built-in Variables::.). The input is read in units called "records", and processed by the rules of your program one record at a time. By default, each record is one line. Each record is automatically split into chunks called "fields". This makes it more convenient for programs to work on the parts of a record. On rare occasions you will need to use the `getline' command. The `getline' command is valuable, both because it can do explicit input from any number of files, and because the files used with it do not have to be named on the `awk' command line (*note Explicit Input with `getline': Getline.). * Menu: * Records:: Controlling how data is split into records. * Fields:: An introduction to fields. * Non-Constant Fields:: Non-constant Field Numbers. * Changing Fields:: Changing the Contents of a Field. * Field Separators:: The field separator and how to change it. * Constant Size:: Reading constant width data. * Multiple Line:: Reading multi-line records. * Getline:: Reading files under explicit program control using the `getline' function.  File: gawk.info, Node: Records, Next: Fields, Prev: Reading Files, Up: Reading Files How Input is Split into Records =============================== The `awk' utility divides the input for your `awk' program into records and fields. Records are separated by a character called the "record separator". By default, the record separator is the newline character. This is why records are, by default, single lines. You can use a different character for the record separator by assigning the character to the built-in variable `RS'. You can change the value of `RS' in the `awk' program, like any other variable, with the assignment operator, `=' (*note Assignment Expressions: Assignment Ops.). The new record-separator character should be enclosed in quotation marks, which indicate a string constant. Often the right time to do this is at the beginning of execution, before any input has been processed, so that the very first record will be read with the proper separator. To do this, use the special `BEGIN' pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). For example: awk 'BEGIN { RS = "/" } ; { print $0 }' BBS-list changes the value of `RS' to `"/"', before reading any input. This is a string whose first character is a slash; as a result, records are separated by slashes. Then the input file is read, and the second rule in the `awk' program (the action with no pattern) prints each record. Since each `print' statement adds a newline at the end of its output, the effect of this `awk' program is to copy the input with each slash changed to a newline. Here are the results of running the program on `BBS-list': $ awk 'BEGIN { RS = "/" } ; { print $0 }' BBS-list -| aardvark 555-5553 1200 -| 300 B -| alpo-net 555-3412 2400 -| 1200 -| 300 A -| barfly 555-7685 1200 -| 300 A -| bites 555-1675 2400 -| 1200 -| 300 A -| camelot 555-0542 300 C -| core 555-2912 1200 -| 300 C -| fooey 555-1234 2400 -| 1200 -| 300 B -| foot 555-6699 1200 -| 300 B -| macfoo 555-6480 1200 -| 300 A -| sdace 555-3430 2400 -| 1200 -| 300 A -| sabafoo 555-2127 1200 -| 300 C -| Note that the entry for the `camelot' BBS is not split. In the original data file (*note Data Files for the Examples: Sample Data Files.), the line looks like this: camelot 555-0542 300 C It only has one baud rate; there are no slashes in the record. Another way to change the record separator is on the command line, using the variable-assignment feature (*note Other Command Line Arguments: Other Arguments.). awk '{ print $0 }' RS="/" BBS-list This sets `RS' to `/' before processing `BBS-list'. Using an unusual character such as `/' for the record separator produces correct behavior in the vast majority of cases. However, the following (extreme) pipeline prints a surprising `1'. There is one field, consisting of a newline. The value of the built-in variable `NF' is the number of fields in the current record. $ echo | awk 'BEGIN { RS = "a" } ; { print NF }' -| 1 Reaching the end of an input file terminates the current input record, even if the last character in the file is not the character in `RS' (d.c.). The empty string, `""' (a string of no characters), has a special meaning as the value of `RS': it means that records are separated by one or more blank lines, and nothing else. *Note Multiple-Line Records: Multiple Line, for more details. If you change the value of `RS' in the middle of an `awk' run, the new value is used to delimit subsequent records, but the record currently being processed (and records already processed) are not affected. After the end of the record has been determined, `gawk' sets the variable `RT' to the text in the input that matched `RS'. The value of `RS' is in fact not limited to a one-character string. It can be any regular expression (*note Regular Expressions: Regexp.). In general, each record ends at the next string that matches the regular expression; the next record starts at the end of the matching string. This general rule is actually at work in the usual case, where `RS' contains just a newline: a record ends at the beginning of the next matching string (the next newline in the input) and the following record starts just after the end of this string (at the first character of the following line). The newline, since it matches `RS', is not part of either record. When `RS' is a single character, `RT' will contain the same single character. However, when `RS' is a regular expression, then `RT' becomes more useful; it contains the actual input text that matched the regular expression. The following example illustrates both of these features. It sets `RS' equal to a regular expression that matches either a newline, or a series of one or more upper-case letters with optional leading and/or trailing white space (*note Regular Expressions: Regexp.). $ echo record 1 AAAA record 2 BBBB record 3 | > gawk 'BEGIN { RS = "\n|( *[[:upper:]]+ *)" } > { print "Record =", $0, "and RT =", RT }' -| Record = record 1 and RT = AAAA -| Record = record 2 and RT = BBBB -| Record = record 3 and RT = -| The final line of output has an extra blank line. This is because the value of `RT' is a newline, and then the `print' statement supplies its own terminating newline. *Note A Simple Stream Editor: Simple Sed, for a more useful example of `RS' as a regexp and `RT'. The use of `RS' as a regular expression and the `RT' variable are `gawk' extensions; they are not available in compatibility mode (*note Command Line Options: Options.). In compatibility mode, only the first character of the value of `RS' is used to determine the end of the record. The `awk' utility keeps track of the number of records that have been read so far from the current input file. This value is stored in a built-in variable called `FNR'. It is reset to zero when a new file is started. Another built-in variable, `NR', is the total number of input records read so far from all data files. It starts at zero but is never automatically reset to zero.  File: gawk.info, Node: Fields, Next: Non-Constant Fields, Prev: Records, Up: Reading Files Examining Fields ================ When `awk' reads an input record, the record is automatically separated or "parsed" by the interpreter into chunks called "fields". By default, fields are separated by whitespace, like words in a line. Whitespace in `awk' means any string of one or more spaces, tabs or newlines;(1) other characters such as formfeed, and so on, that are considered whitespace by other languages are *not* considered whitespace by `awk'. The purpose of fields is to make it more convenient for you to refer to these pieces of the record. You don't have to use them--you can operate on the whole record if you wish--but fields are what make simple `awk' programs so powerful. To refer to a field in an `awk' program, you use a dollar-sign, `$', followed by the number of the field you want. Thus, `$1' refers to the first field, `$2' to the second, and so on. For example, suppose the following is a line of input: This seems like a pretty nice example. Here the first field, or `$1', is `This'; the second field, or `$2', is `seems'; and so on. Note that the last field, `$7', is `example.'. Because there is no space between the `e' and the `.', the period is considered part of the seventh field. `NF' is a built-in variable whose value is the number of fields in the current record. `awk' updates the value of `NF' automatically, each time a record is read. No matter how many fields there are, the last field in a record can be represented by `$NF'. So, in the example above, `$NF' would be the same as `$7', which is `example.'. Why this works is explained below (*note Non-constant Field Numbers: Non-Constant Fields.). If you try to reference a field beyond the last one, such as `$8' when the record has only seven fields, you get the empty string. `$0', which looks like a reference to the "zeroth" field, is a special case: it represents the whole input record. `$0' is used when you are not interested in fields. Here are some more examples: $ awk '$1 ~ /foo/ { print $0 }' BBS-list -| fooey 555-1234 2400/1200/300 B -| foot 555-6699 1200/300 B -| macfoo 555-6480 1200/300 A -| sabafoo 555-2127 1200/300 C This example prints each record in the file `BBS-list' whose first field contains the string `foo'. The operator `~' is called a "matching operator" (*note How to Use Regular Expressions: Regexp Usage.); it tests whether a string (here, the field `$1') matches a given regular expression. By contrast, the following example looks for `foo' in *the entire record* and prints the first field and the last field for each input record containing a match. $ awk '/foo/ { print $1, $NF }' BBS-list -| fooey B -| foot B -| macfoo A -| sabafoo C ---------- Footnotes ---------- (1) In POSIX `awk', newlines are not considered whitespace for separating fields.  File: gawk.info, Node: Non-Constant Fields, Next: Changing Fields, Prev: Fields, Up: Reading Files Non-constant Field Numbers ========================== The number of a field does not need to be a constant. Any expression in the `awk' language can be used after a `$' to refer to a field. The value of the expression specifies the field number. If the value is a string, rather than a number, it is converted to a number. Consider this example: awk '{ print $NR }' Recall that `NR' is the number of records read so far: one in the first record, two in the second, etc. So this example prints the first field of the first record, the second field of the second record, and so on. For the twentieth record, field number 20 is printed; most likely, the record has fewer than 20 fields, so this prints a blank line. Here is another example of using expressions as field numbers: awk '{ print $(2*2) }' BBS-list `awk' must evaluate the expression `(2*2)' and use its value as the number of the field to print. The `*' sign represents multiplication, so the expression `2*2' evaluates to four. The parentheses are used so that the multiplication is done before the `$' operation; they are necessary whenever there is a binary operator in the field-number expression. This example, then, prints the hours of operation (the fourth field) for every line of the file `BBS-list'. (All of the `awk' operators are listed, in order of decreasing precedence, in *Note Operator Precedence (How Operators Nest): Precedence.) If the field number you compute is zero, you get the entire record. Thus, `$(2-2)' has the same value as `$0'. Negative field numbers are not allowed; trying to reference one will usually terminate your running `awk' program. (The POSIX standard does not define what happens when you reference a negative field number. `gawk' will notice this and terminate your program. Other `awk' implementations may behave differently.) As mentioned in *Note Examining Fields: Fields, the number of fields in the current record is stored in the built-in variable `NF' (also *note Built-in Variables::.). The expression `$NF' is not a special feature: it is the direct consequence of evaluating `NF' and using its value as a field number.  File: gawk.info, Node: Changing Fields, Next: Field Separators, Prev: Non-Constant Fields, Up: Reading Files Changing the Contents of a Field ================================ You can change the contents of a field as seen by `awk' within an `awk' program; this changes what `awk' perceives as the current input record. (The actual input is untouched; `awk' *never* modifies the input file.) Consider this example and its output: $ awk '{ $3 = $2 - 10; print $2, $3 }' inventory-shipped -| 13 3 -| 15 5 -| 15 5 ... The `-' sign represents subtraction, so this program reassigns field three, `$3', to be the value of field two minus ten, `$2 - 10'. (*Note Arithmetic Operators: Arithmetic Ops.) Then field two, and the new value for field three, are printed. In order for this to work, the text in field `$2' must make sense as a number; the string of characters must be converted to a number in order for the computer to do arithmetic on it. The number resulting from the subtraction is converted back to a string of characters which then becomes field three. *Note Conversion of Strings and Numbers: Conversion. When you change the value of a field (as perceived by `awk'), the text of the input record is recalculated to contain the new field where the old one was. Therefore, `$0' changes to reflect the altered field. Thus, this program prints a copy of the input file, with 10 subtracted from the second field of each line. $ awk '{ $2 = $2 - 10; print $0 }' inventory-shipped -| Jan 3 25 15 115 -| Feb 5 32 24 226 -| Mar 5 24 34 228 ... You can also assign contents to fields that are out of range. For example: $ awk '{ $6 = ($5 + $4 + $3 + $2) > print $6 }' inventory-shipped -| 168 -| 297 -| 301 ... We've just created `$6', whose value is the sum of fields `$2', `$3', `$4', and `$5'. The `+' sign represents addition. For the file `inventory-shipped', `$6' represents the total number of parcels shipped for a particular month. Creating a new field changes `awk''s internal copy of the current input record--the value of `$0'. Thus, if you do `print $0' after adding a field, the record printed includes the new field, with the appropriate number of field separators between it and the previously existing fields. This recomputation affects and is affected by `NF' (the number of fields; *note Examining Fields: Fields.), and by a feature that has not been discussed yet, the "output field separator", `OFS', which is used to separate the fields (*note Output Separators::.). For example, the value of `NF' is set to the number of the highest field you create. Note, however, that merely *referencing* an out-of-range field does *not* change the value of either `$0' or `NF'. Referencing an out-of-range field only produces an empty string. For example: if ($(NF+1) != "") print "can't happen" else print "everything is normal" should print `everything is normal', because `NF+1' is certain to be out of range. (*Note The `if'-`else' Statement: If Statement, for more information about `awk''s `if-else' statements. *Note Variable Typing and Comparison Expressions: Typing and Comparison, for more information about the `!=' operator.) It is important to note that making an assignment to an existing field will change the value of `$0', but will not change the value of `NF', even when you assign the empty string to a field. For example: $ echo a b c d | awk '{ OFS = ":"; $2 = "" > print $0; print NF }' -| a::c:d -| 4 The field is still there; it just has an empty value. You can tell because there are two colons in a row. This example shows what happens if you create a new field. $ echo a b c d | awk '{ OFS = ":"; $2 = ""; $6 = "new" > print $0; print NF }' -| a::c:d::new -| 6 The intervening field, `$5' is created with an empty value (indicated by the second pair of adjacent colons), and `NF' is updated with the value six. Finally, decrementing `NF' will lose the values of the fields after the new value of `NF', and `$0' will be recomputed. Here is an example: $ echo a b c d e f | ../gawk '{ print "NF =", NF; > NF = 3; print $0 }' -| NF = 6 -| a b c  File: gawk.info, Node: Field Separators, Next: Constant Size, Prev: Changing Fields, Up: Reading Files Specifying How Fields are Separated =================================== This section is rather long; it describes one of the most fundamental operations in `awk'. * Menu: * Basic Field Splitting:: How fields are split with single characters or simple strings. * Regexp Field Splitting:: Using regexps as the field separator. * Single Character Fields:: Making each character a separate field. * Command Line Field Separator:: Setting `FS' from the command line. * Field Splitting Summary:: Some final points and a summary table.  File: gawk.info, Node: Basic Field Splitting, Next: Regexp Field Splitting, Prev: Field Separators, Up: Field Separators The Basics of Field Separating ------------------------------ The "field separator", which is either a single character or a regular expression, controls the way `awk' splits an input record into fields. `awk' scans the input record for character sequences that match the separator; the fields themselves are the text between the matches. In the examples below, we use the bullet symbol "*" to represent spaces in the output. If the field separator is `oo', then the following line: moo goo gai pan would be split into three fields: `m', `*g' and `*gai*pan'. Note the leading spaces in the values of the second and third fields. The field separator is represented by the built-in variable `FS'. Shell programmers take note! `awk' does *not* use the name `IFS' which is used by the POSIX compatible shells (such as the Bourne shell, `sh', or the GNU Bourne-Again Shell, Bash). You can change the value of `FS' in the `awk' program with the assignment operator, `=' (*note Assignment Expressions: Assignment Ops.). Often the right time to do this is at the beginning of execution, before any input has been processed, so that the very first record will be read with the proper separator. To do this, use the special `BEGIN' pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). For example, here we set the value of `FS' to the string `","': awk 'BEGIN { FS = "," } ; { print $2 }' Given the input line, John Q. Smith, 29 Oak St., Walamazoo, MI 42139 this `awk' program extracts and prints the string `*29*Oak*St.'. Sometimes your input data will contain separator characters that don't separate fields the way you thought they would. For instance, the person's name in the example we just used might have a title or suffix attached, such as `John Q. Smith, LXIX'. From input containing such a name: John Q. Smith, LXIX, 29 Oak St., Walamazoo, MI 42139 the above program would extract `*LXIX', instead of `*29*Oak*St.'. If you were expecting the program to print the address, you would be surprised. The moral is: choose your data layout and separator characters carefully to prevent such problems. Normally, fields are separated by whitespace sequences (spaces, tabs and newlines), not by single spaces: two spaces in a row do not delimit an empty field. The default value of the field separator `FS' is a string containing a single space, `" "'. If this value were interpreted in the usual way, each space character would separate fields, so two spaces in a row would make an empty field between them. The reason this does not happen is that a single space as the value of `FS' is a special case: it is taken to specify the default manner of delimiting fields. If `FS' is any other single character, such as `","', then each occurrence of that character separates two fields. Two consecutive occurrences delimit an empty field. If the character occurs at the beginning or the end of the line, that too delimits an empty field. The space character is the only single character which does not follow these rules.  File: gawk.info, Node: Regexp Field Splitting, Next: Single Character Fields, Prev: Basic Field Splitting, Up: Field Separators Using Regular Expressions to Separate Fields -------------------------------------------- The previous node discussed the use of single characters or simple strings as the value of `FS'. More generally, the value of `FS' may be a string containing any regular expression. In this case, each match in the record for the regular expression separates fields. For example, the assignment: FS = ", \t" makes every area of an input line that consists of a comma followed by a space and a tab, into a field separator. (`\t' is an "escape sequence" that stands for a tab; *note Escape Sequences::., for the complete list of similar escape sequences.) For a less trivial example of a regular expression, suppose you want single spaces to separate fields the way single commas were used above. You can set `FS' to `"[ ]"' (left bracket, space, right bracket). This regular expression matches a single space and nothing else (*note Regular Expressions: Regexp.). There is an important difference between the two cases of `FS = " "' (a single space) and `FS = "[ \t\n]+"' (left bracket, space, backslash, "t", backslash, "n", right bracket, which is a regular expression matching one or more spaces, tabs, or newlines). For both values of `FS', fields are separated by runs of spaces, tabs and/or newlines. However, when the value of `FS' is `" "', `awk' will first strip leading and trailing whitespace from the record, and then decide where the fields are. For example, the following pipeline prints `b': $ echo ' a b c d ' | awk '{ print $2 }' -| b However, this pipeline prints `a' (note the extra spaces around each letter): $ echo ' a b c d ' | awk 'BEGIN { FS = "[ \t]+" } > { print $2 }' -| a In this case, the first field is "null", or empty. The stripping of leading and trailing whitespace also comes into play whenever `$0' is recomputed. For instance, study this pipeline: $ echo ' a b c d' | awk '{ print; $2 = $2; print }' -| a b c d -| a b c d The first `print' statement prints the record as it was read, with leading whitespace intact. The assignment to `$2' rebuilds `$0' by concatenating `$1' through `$NF' together, separated by the value of `OFS'. Since the leading whitespace was ignored when finding `$1', it is not part of the new `$0'. Finally, the last `print' statement prints the new `$0'.  File: gawk.info, Node: Single Character Fields, Next: Command Line Field Separator, Prev: Regexp Field Splitting, Up: Field Separators Making Each Character a Separate Field -------------------------------------- There are times when you may want to examine each character of a record separately. In `gawk', this is easy to do, you simply assign the null string (`""') to `FS'. In this case, each individual character in the record will become a separate field. Here is an example: $ echo a b | gawk 'BEGIN { FS = "" } > { > for (i = 1; i <= NF; i = i + 1) > print "Field", i, "is", $i > }' -| Field 1 is a -| Field 2 is -| Field 3 is b Traditionally, the behavior for `FS' equal to `""' was not defined. In this case, Unix `awk' would simply treat the entire record as only having one field (d.c.). In compatibility mode (*note Command Line Options: Options.), if `FS' is the null string, then `gawk' will also behave this way.  File: gawk.info, Node: Command Line Field Separator, Next: Field Splitting Summary, Prev: Single Character Fields, Up: Field Separators Setting `FS' from the Command Line ---------------------------------- `FS' can be set on the command line. You use the `-F' option to do so. For example: awk -F, 'PROGRAM' INPUT-FILES sets `FS' to be the `,' character. Notice that the option uses a capital `F'. Contrast this with `-f', which specifies a file containing an `awk' program. Case is significant in command line options: the `-F' and `-f' options have nothing to do with each other. You can use both options at the same time to set the `FS' variable *and* get an `awk' program from a file. The value used for the argument to `-F' is processed in exactly the same way as assignments to the built-in variable `FS'. This means that if the field separator contains special characters, they must be escaped appropriately. For example, to use a `\' as the field separator, you would have to type: # same as FS = "\\" awk -F\\\\ '...' files ... Since `\' is used for quoting in the shell, `awk' will see `-F\\'. Then `awk' processes the `\\' for escape characters (*note Escape Sequences::.), finally yielding a single `\' to be used for the field separator. As a special case, in compatibility mode (*note Command Line Options: Options.), if the argument to `-F' is `t', then `FS' is set to the tab character. This is because if you type `-F\t' at the shell, without any quotes, the `\' gets deleted, so `awk' figures that you really want your fields to be separated with tabs, and not `t's. Use `-v FS="t"' on the command line if you really do want to separate your fields with `t's (*note Command Line Options: Options.). For example, let's use an `awk' program file called `baud.awk' that contains the pattern `/300/', and the action `print $1'. Here is the program: /300/ { print $1 } Let's also set `FS' to be the `-' character, and run the program on the file `BBS-list'. The following command prints a list of the names of the bulletin boards that operate at 300 baud and the first three digits of their phone numbers: $ awk -F- -f baud.awk BBS-list -| aardvark 555 -| alpo -| barfly 555 ... Note the second line of output. In the original file (*note Data Files for the Examples: Sample Data Files.), the second line looked like this: alpo-net 555-3412 2400/1200/300 A The `-' as part of the system's name was used as the field separator, instead of the `-' in the phone number that was originally intended. This demonstrates why you have to be careful in choosing your field and record separators. On many Unix systems, each user has a separate entry in the system password file, one line per user. The information in these lines is separated by colons. The first field is the user's logon name, and the second is the user's encrypted password. A password file entry might look like this: arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh The following program searches the system password file, and prints the entries for users who have no password: awk -F: '$2 == ""' /etc/passwd  File: gawk.info, Node: Field Splitting Summary, Prev: Command Line Field Separator, Up: Field Separators Field Splitting Summary ----------------------- According to the POSIX standard, `awk' is supposed to behave as if each record is split into fields at the time that it is read. In particular, this means that you can change the value of `FS' after a record is read, and the value of the fields (i.e. how they were split) should reflect the old value of `FS', not the new one. However, many implementations of `awk' do not work this way. Instead, they defer splitting the fields until a field is actually referenced. The fields will be split using the *current* value of `FS'! (d.c.) This behavior can be difficult to diagnose. The following example illustrates the difference between the two methods. (The `sed'(1) command prints just the first line of `/etc/passwd'.) sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }' will usually print root on an incorrect implementation of `awk', while `gawk' will print something like root:nSijPlPhZZwgE:0:0:Root:/: The following table summarizes how fields are split, based on the value of `FS'. (`==' means "is equal to.") `FS == " "' Fields are separated by runs of whitespace. Leading and trailing whitespace are ignored. This is the default. `FS == ANY OTHER SINGLE CHARACTER' Fields are separated by each occurrence of the character. Multiple successive occurrences delimit empty fields, as do leading and trailing occurrences. The character can even be a regexp metacharacter; it does not need to be escaped. `FS == REGEXP' Fields are separated by occurrences of characters that match REGEXP. Leading and trailing matches of REGEXP delimit empty fields. `FS == ""' Each individual character in the record becomes a separate field. ---------- Footnotes ---------- (1) The `sed' utility is a "stream editor." Its behavior is also defined by the POSIX standard.  File: gawk.info, Node: Constant Size, Next: Multiple Line, Prev: Field Separators, Up: Reading Files Reading Fixed-width Data ======================== (This section discusses an advanced, experimental feature. If you are a novice `awk' user, you may wish to skip it on the first reading.) `gawk' version 2.13 introduced a new facility for dealing with fixed-width fields with no distinctive field separator. Data of this nature arises, for example, in the input for old FORTRAN programs where numbers are run together; or in the output of programs that did not anticipate the use of their output as input for other programs. An example of the latter is a table where all the columns are lined up by the use of a variable number of spaces and *empty fields are just spaces*. Clearly, `awk''s normal field splitting based on `FS' will not work well in this case. Although a portable `awk' program can use a series of `substr' calls on `$0' (*note Built-in Functions for String Manipulation: String Functions.), this is awkward and inefficient for a large number of fields. The splitting of an input record into fixed-width fields is specified by assigning a string containing space-separated numbers to the built-in variable `FIELDWIDTHS'. Each number specifies the width of the field *including* columns between fields. If you want to ignore the columns between fields, you can specify the width as a separate field that is subsequently ignored. The following data is the output of the Unix `w' utility. It is useful to illustrate the use of `FIELDWIDTHS'. 10:06pm up 21 days, 14:04, 23 users User tty login idle JCPU PCPU what hzuo ttyV0 8:58pm 9 5 vi p24.tex hzang ttyV3 6:37pm 50 -csh eklye ttyV5 9:53pm 7 1 em thes.tex dportein ttyV6 8:17pm 1:47 -csh gierd ttyD3 10:00pm 1 elm dave ttyD4 9:47pm 4 4 w brent ttyp0 26Jun91 4:46 26:46 4:41 bash dave ttyq4 26Jun9115days 46 46 wnewmail The following program takes the above input, converts the idle time to number of seconds and prints out the first two fields and the calculated idle time. (This program uses a number of `awk' features that haven't been introduced yet.) BEGIN { FIELDWIDTHS = "9 6 10 6 7 7 35" } NR > 2 { idle = $4 sub(/^ */, "", idle) # strip leading spaces if (idle == "") idle = 0 if (idle ~ /:/) { split(idle, t, ":") idle = t[1] * 60 + t[2] } if (idle ~ /days/) idle *= 24 * 60 * 60 print $1, $2, idle } Here is the result of running the program on the data: hzuo ttyV0 0 hzang ttyV3 50 eklye ttyV5 0 dportein ttyV6 107 gierd ttyD3 1 dave ttyD4 0 brent ttyp0 286 dave ttyq4 1296000 Another (possibly more practical) example of fixed-width input data would be the input from a deck of balloting cards. In some parts of the United States, voters mark their choices by punching holes in computer cards. These cards are then processed to count the votes for any particular candidate or on any particular issue. Since a voter may choose not to vote on some issue, any column on the card may be empty. An `awk' program for processing such data could use the `FIELDWIDTHS' feature to simplify reading the data. (Of course, getting `gawk' to run on a system with card readers is another story!) Assigning a value to `FS' causes `gawk' to return to using `FS' for field splitting. Use `FS = FS' to make this happen, without having to know the current value of `FS'. This feature is still experimental, and may evolve over time. Note that in particular, `gawk' does not attempt to verify the sanity of the values used in the value of `FIELDWIDTHS'.  File: gawk.info, Node: Multiple Line, Next: Getline, Prev: Constant Size, Up: Reading Files Multiple-Line Records ===================== In some data bases, a single line cannot conveniently hold all the information in one entry. In such cases, you can use multi-line records. The first step in doing this is to choose your data format: when records are not defined as single lines, how do you want to define them? What should separate records? One technique is to use an unusual character or string to separate records. For example, you could use the formfeed character (written `\f' in `awk', as in C) to separate them, making each record a page of the file. To do this, just set the variable `RS' to `"\f"' (a string containing the formfeed character). Any other character could equally well be used, as long as it won't be part of the data in a record. Another technique is to have blank lines separate records. By a special dispensation, an empty string as the value of `RS' indicates that records are separated by one or more blank lines. If you set `RS' to the empty string, a record always ends at the first blank line encountered. And the next record doesn't start until the first non-blank line that follows--no matter how many blank lines appear in a row, they are considered one record-separator. You can achieve the same effect as `RS = ""' by assigning the string `"\n\n+"' to `RS'. This regexp matches the newline at the end of the record, and one or more blank lines after the record. In addition, a regular expression always matches the longest possible sequence when there is a choice (*note How Much Text Matches?: Leftmost Longest.). So the next record doesn't start until the first non-blank line that follows--no matter how many blank lines appear in a row, they are considered one record-separator. There is an important difference between `RS = ""' and `RS = "\n\n+"'. In the first case, leading newlines in the input data file are ignored, and if a file ends without extra blank lines after the last record, the final newline is removed from the record. In the second case, this special processing is not done (d.c.). Now that the input is separated into records, the second step is to separate the fields in the record. One way to do this is to divide each of the lines into fields in the normal manner. This happens by default as the result of a special feature: when `RS' is set to the empty string, the newline character *always* acts as a field separator. This is in addition to whatever field separations result from `FS'. The original motivation for this special exception was probably to provide useful behavior in the default case (i.e. `FS' is equal to `" "'). This feature can be a problem if you really don't want the newline character to separate fields, since there is no way to prevent it. However, you can work around this by using the `split' function to break up the record manually (*note Built-in Functions for String Manipulation: String Functions.). Another way to separate fields is to put each field on a separate line: to do this, just set the variable `FS' to the string `"\n"'. (This simple regular expression matches a single newline.) A practical example of a data file organized this way might be a mailing list, where each entry is separated by blank lines. If we have a mailing list in a file named `addresses', that looks like this: Jane Doe 123 Main Street Anywhere, SE 12345-6789 John Smith 456 Tree-lined Avenue Smallville, MW 98765-4321 ... A simple program to process this file would look like this: # addrs.awk --- simple mailing list program # Records are separated by blank lines. # Each line is one field. BEGIN { RS = "" ; FS = "\n" } { print "Name is:", $1 print "Address is:", $2 print "City and State are:", $3 print "" } Running the program produces the following output: $ awk -f addrs.awk addresses -| Name is: Jane Doe -| Address is: 123 Main Street -| City and State are: Anywhere, SE 12345-6789 -| -| Name is: John Smith -| Address is: 456 Tree-lined Avenue -| City and State are: Smallville, MW 98765-4321 -| ... *Note Printing Mailing Labels: Labels Program, for a more realistic program that deals with address lists. The following table summarizes how records are split, based on the value of `RS'. (`==' means "is equal to.") `RS == "\n"' Records are separated by the newline character (`\n'). In effect, every line in the data file is a separate record, including blank lines. This is the default. `RS == ANY SINGLE CHARACTER' Records are separated by each occurrence of the character. Multiple successive occurrences delimit empty records. `RS == ""' Records are separated by runs of blank lines. The newline character always serves as a field separator, in addition to whatever value `FS' may have. Leading and trailing newlines in a file are ignored. `RS == REGEXP' Records are separated by occurrences of characters that match REGEXP. Leading and trailing matches of REGEXP delimit empty records. In all cases, `gawk' sets `RT' to the input text that matched the value specified by `RS'.  File: gawk.info, Node: Getline, Prev: Multiple Line, Up: Reading Files Explicit Input with `getline' ============================= So far we have been getting our input data from `awk''s main input stream--either the standard input (usually your terminal, sometimes the output from another program) or from the files specified on the command line. The `awk' language has a special built-in command called `getline' that can be used to read input under your explicit control. * Menu: * Getline Intro:: Introduction to the `getline' function. * Plain Getline:: Using `getline' with no arguments. * Getline/Variable:: Using `getline' into a variable. * Getline/File:: Using `getline' from a file. * Getline/Variable/File:: Using `getline' into a variable from a file. * Getline/Pipe:: Using `getline' from a pipe. * Getline/Variable/Pipe:: Using `getline' into a variable from a pipe. * Getline Summary:: Summary Of `getline' Variants.  File: gawk.info, Node: Getline Intro, Next: Plain Getline, Prev: Getline, Up: Getline Introduction to `getline' ------------------------- This command is used in several different ways, and should *not* be used by beginners. It is covered here because this is the chapter on input. The examples that follow the explanation of the `getline' command include material that has not been covered yet. Therefore, come back and study the `getline' command *after* you have reviewed the rest of this Info file and have a good knowledge of how `awk' works. `getline' returns one if it finds a record, and zero if the end of the file is encountered. If there is some error in getting a record, such as a file that cannot be opened, then `getline' returns -1. In this case, `gawk' sets the variable `ERRNO' to a string describing the error that occurred. In the following examples, COMMAND stands for a string value that represents a shell command.  File: gawk.info, Node: Plain Getline, Next: Getline/Variable, Prev: Getline Intro, Up: Getline Using `getline' with No Arguments --------------------------------- The `getline' command can be used without arguments to read input from the current input file. All it does in this case is read the next input record and split it up into fields. This is useful if you've finished processing the current record, but you want to do some special processing *right now* on the next record. Here's an example: awk '{ if ((t = index($0, "/*")) != 0) { # value will be "" if t is 1 tmp = substr($0, 1, t - 1) u = index(substr($0, t + 2), "*/") while (u == 0) { if (getline <= 0) { m = "unexpected EOF or error" m = (m ": " ERRNO) print m > "/dev/stderr" exit } t = -1 u = index($0, "*/") } # substr expression will be "" if */ # occurred at end of line $0 = tmp substr($0, t + u + 3) } print $0 }' This `awk' program deletes all C-style comments, `/* ... */', from the input. By replacing the `print $0' with other statements, you could perform more complicated processing on the decommented input, like searching for matches of a regular expression. This program has a subtle problem--it does not work if one comment ends and another begins on the same line. This form of the `getline' command sets `NF' (the number of fields; *note Examining Fields: Fields.), `NR' (the number of records read so far; *note How Input is Split into Records: Records.), `FNR' (the number of records read from this input file), and the value of `$0'. *Note:* the new value of `$0' is used in testing the patterns of any subsequent rules. The original value of `$0' that triggered the rule which executed `getline' is lost (d.c.). By contrast, the `next' statement reads a new record but immediately begins processing it normally, starting with the first rule in the program. *Note The `next' Statement: Next Statement.  File: gawk.info, Node: Getline/Variable, Next: Getline/File, Prev: Plain Getline, Up: Getline Using `getline' Into a Variable ------------------------------- You can use `getline VAR' to read the next record from `awk''s input into the variable VAR. No other processing is done. For example, suppose the next line is a comment, or a special string, and you want to read it, without triggering any rules. This form of `getline' allows you to read that line and store it in a variable so that the main read-a-line-and-check-each-rule loop of `awk' never sees it. The following example swaps every two lines of input. For example, given: wan tew free phore it outputs: tew wan phore free Here's the program: awk '{ if ((getline tmp) > 0) { print tmp print $0 } else print $0 }' The `getline' command used in this way sets only the variables `NR' and `FNR' (and of course, VAR). The record is not split into fields, so the values of the fields (including `$0') and the value of `NF' do not change.  File: gawk.info, Node: Getline/File, Next: Getline/Variable/File, Prev: Getline/Variable, Up: Getline Using `getline' from a File --------------------------- Use `getline < FILE' to read the next record from the file FILE. Here FILE is a string-valued expression that specifies the file name. `< FILE' is called a "redirection" since it directs input to come from a different place. For example, the following program reads its input record from the file `secondary.input' when it encounters a first field with a value equal to 10 in the current input file. awk '{ if ($1 == 10) { getline < "secondary.input" print } else print }' Since the main input stream is not used, the values of `NR' and `FNR' are not changed. But the record read is split into fields in the normal manner, so the values of `$0' and other fields are changed. So is the value of `NF'. According to POSIX, `getline < EXPRESSION' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `getline < dir "/" file' is ambiguous because the concatenation operator is not parenthesized, and you should write it as `getline < (dir "/" file)' if you want your program to be portable to other `awk' implementations.  File: gawk.info, Node: Getline/Variable/File, Next: Getline/Pipe, Prev: Getline/File, Up: Getline Using `getline' Into a Variable from a File ------------------------------------------- Use `getline VAR < FILE' to read input the file FILE and put it in the variable VAR. As above, FILE is a string-valued expression that specifies the file from which to read. In this version of `getline', none of the built-in variables are changed, and the record is not split into fields. The only variable changed is VAR. According to POSIX, `getline VAR < EXPRESSION' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `getline < dir "/" file' is ambiguous because the concatenation operator is not parenthesized, and you should write it as `getline < (dir "/" file)' if you want your program to be portable to other `awk' implementations. For example, the following program copies all the input files to the output, except for records that say `@@include FILENAME'. Such a record is replaced by the contents of the file FILENAME. awk '{ if (NF == 2 && $1 == "@@include") { while ((getline line < $2) > 0) print line close($2) } else print }' Note here how the name of the extra input file is not built into the program; it is taken directly from the data, from the second field on the `@@include' line. The `close' function is called to ensure that if two identical `@@include' lines appear in the input, the entire specified file is included twice. *Note Closing Input and Output Files and Pipes: Close Files And Pipes. One deficiency of this program is that it does not process nested `@@include' statements (`@@include' statements in included files) the way a true macro preprocessor would. *Note An Easy Way to Use Library Functions: Igawk Program, for a program that does handle nested `@@include' statements.  File: gawk.info, Node: Getline/Pipe, Next: Getline/Variable/Pipe, Prev: Getline/Variable/File, Up: Getline Using `getline' from a Pipe --------------------------- You can pipe the output of a command into `getline', using `COMMAND | getline'. In this case, the string COMMAND is run as a shell command and its output is piped into `awk' to be used as input. This form of `getline' reads one record at a time from the pipe. For example, the following program copies its input to its output, except for lines that begin with `@@execute', which are replaced by the output produced by running the rest of the line as a shell command: awk '{ if ($1 == "@@execute") { tmp = substr($0, 10) while ((tmp | getline) > 0) print close(tmp) } else print }' The `close' function is called to ensure that if two identical `@@execute' lines appear in the input, the command is run for each one. *Note Closing Input and Output Files and Pipes: Close Files And Pipes. Given the input: foo bar baz @@execute who bletch the program might produce: foo bar baz arnold ttyv0 Jul 13 14:22 miriam ttyp0 Jul 13 14:23 (murphy:0) bill ttyp1 Jul 13 14:23 (murphy:0) bletch Notice that this program ran the command `who' and printed the result. (If you try this program yourself, you will of course get different results, showing you who is logged in on your system.) This variation of `getline' splits the record into fields, sets the value of `NF' and recomputes the value of `$0'. The values of `NR' and `FNR' are not changed. According to POSIX, `EXPRESSION | getline' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `"echo " "date" | getline' is ambiguous because the concatenation operator is not parenthesized, and you should write it as `("echo " "date") | getline' if you want your program to be portable to other `awk' implementations.  File: gawk.info, Node: Getline/Variable/Pipe, Next: Getline Summary, Prev: Getline/Pipe, Up: Getline Using `getline' Into a Variable from a Pipe ------------------------------------------- When you use `COMMAND | getline VAR', the output of the command COMMAND is sent through a pipe to `getline' and into the variable VAR. For example, the following program reads the current date and time into the variable `current_time', using the `date' utility, and then prints it. awk 'BEGIN { "date" | getline current_time close("date") print "Report printed on " current_time }' In this version of `getline', none of the built-in variables are changed, and the record is not split into fields. According to POSIX, `EXPRESSION | getline VAR' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `"echo " "date" | getline VAR' is ambiguous because the concatenation operator is not parenthesized, and you should write it as `("echo " "date") | getline VAR' if you want your program to be portable to other `awk' implementations.  File: gawk.info, Node: Getline Summary, Prev: Getline/Variable/Pipe, Up: Getline Summary of `getline' Variants ----------------------------- With all the forms of `getline', even though `$0' and `NF', may be updated, the record will not be tested against all the patterns in the `awk' program, in the way that would happen if the record were read normally by the main processing loop of `awk'. However the new record is tested against any subsequent rules. Many `awk' implementations limit the number of pipelines an `awk' program may have open to just one! In `gawk', there is no such limit. You can open as many pipelines as the underlying operating system will permit. An interesting side-effect occurs if you use `getline' (without a redirection) inside a `BEGIN' rule. Since an unredirected `getline' reads from the command line data files, the first `getline' command causes `awk' to set the value of `FILENAME'. Normally, `FILENAME' does not have a value inside `BEGIN' rules, since you have not yet started to process the command line data files (d.c.). (*Note The `BEGIN' and `END' Special Patterns: BEGIN/END, also *note Built-in Variables that Convey Information: Auto-set..) The following table summarizes the six variants of `getline', listing which built-in variables are set by each one. `getline' sets `$0', `NF', `FNR', and `NR'. `getline VAR' sets VAR, `FNR', and `NR'. `getline < FILE' sets `$0', and `NF'. `getline VAR < FILE' sets VAR. `COMMAND | getline' sets `$0', and `NF'. `COMMAND | getline VAR' sets VAR.  File: gawk.info, Node: Printing, Next: Expressions, Prev: Reading Files, Up: Top Printing Output *************** One of the most common actions is to "print", or output, some or all of the input. You use the `print' statement for simple output. You use the `printf' statement for fancier formatting. Both are described in this chapter. * Menu: * Print:: The `print' statement. * Print Examples:: Simple examples of `print' statements. * Output Separators:: The output separators and how to change them. * OFMT:: Controlling Numeric Output With `print'. * Printf:: The `printf' statement. * Redirection:: How to redirect output to multiple files and pipes. * Special Files:: File name interpretation in `gawk'. `gawk' allows access to inherited file descriptors. * Close Files And Pipes:: Closing Input and Output Files and Pipes.  File: gawk.info, Node: Print, Next: Print Examples, Prev: Printing, Up: Printing The `print' Statement ===================== The `print' statement does output with simple, standardized formatting. You specify only the strings or numbers to be printed, in a list separated by commas. They are output, separated by single spaces, followed by a newline. The statement looks like this: print ITEM1, ITEM2, ... The entire list of items may optionally be enclosed in parentheses. The parentheses are necessary if any of the item expressions uses the `>' relational operator; otherwise it could be confused with a redirection (*note Redirecting Output of `print' and `printf': Redirection.). The items to be printed can be constant strings or numbers, fields of the current record (such as `$1'), variables, or any `awk' expressions. Numeric values are converted to strings, and then printed. The `print' statement is completely general for computing *what* values to print. However, with two exceptions, you cannot specify *how* to print them--how many columns, whether to use exponential notation or not, and so on. (For the exceptions, *note Output Separators::., and *Note Controlling Numeric Output with `print': OFMT.) For that, you need the `printf' statement (*note Using `printf' Statements for Fancier Printing: Printf.). The simple statement `print' with no items is equivalent to `print $0': it prints the entire current record. To print a blank line, use `print ""', where `""' is the empty string. To print a fixed piece of text, use a string constant such as `"Don't Panic"' as one item. If you forget to use the double-quote characters, your text will be taken as an `awk' expression, and you will probably get an error. Keep in mind that a space is printed between any two items. Each `print' statement makes at least one line of output. But it isn't limited to one line. If an item value is a string that contains a newline, the newline is output along with the rest of the string. A single `print' can make any number of lines this way.  File: gawk.info, Node: Print Examples, Next: Output Separators, Prev: Print, Up: Printing Examples of `print' Statements ============================== Here is an example of printing a string that contains embedded newlines (the `\n' is an escape sequence, used to represent the newline character; see *Note Escape Sequences::): $ awk 'BEGIN { print "line one\nline two\nline three" }' -| line one -| line two -| line three Here is an example that prints the first two fields of each input record, with a space between them: $ awk '{ print $1, $2 }' inventory-shipped -| Jan 13 -| Feb 15 -| Mar 15 ... A common mistake in using the `print' statement is to omit the comma between two items. This often has the effect of making the items run together in the output, with no space. The reason for this is that juxtaposing two string expressions in `awk' means to concatenate them. Here is the same program, without the comma: $ awk '{ print $1 $2 }' inventory-shipped -| Jan13 -| Feb15 -| Mar15 ... To someone unfamiliar with the file `inventory-shipped', neither example's output makes much sense. A heading line at the beginning would make it clearer. Let's add some headings to our table of months (`$1') and green crates shipped (`$2'). We do this using the `BEGIN' pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.) to force the headings to be printed only once: awk 'BEGIN { print "Month Crates" print "----- ------" } { print $1, $2 }' inventory-shipped Did you already guess what happens? When run, the program prints the following: Month Crates ----- ------ Jan 13 Feb 15 Mar 15 ... The headings and the table data don't line up! We can fix this by printing some spaces between the two fields: awk 'BEGIN { print "Month Crates" print "----- ------" } { print $1, " ", $2 }' inventory-shipped You can imagine that this way of lining up columns can get pretty complicated when you have many columns to fix. Counting spaces for two or three columns can be simple, but more than this and you can get lost quite easily. This is why the `printf' statement was created (*note Using `printf' Statements for Fancier Printing: Printf.); one of its specialties is lining up columns of data. As a side point, you can continue either a `print' or `printf' statement simply by putting a newline after any comma (*note `awk' Statements Versus Lines: Statements/Lines.).  File: gawk.info, Node: Output Separators, Next: OFMT, Prev: Print Examples, Up: Printing Output Separators ================= As mentioned previously, a `print' statement contains a list of items, separated by commas. In the output, the items are normally separated by single spaces. This need not be the case; a single space is only the default. You can specify any string of characters to use as the "output field separator" by setting the built-in variable `OFS'. The initial value of this variable is the string `" "', that is, a single space. The output from an entire `print' statement is called an "output record". Each `print' statement outputs one output record and then outputs a string called the "output record separator". The built-in variable `ORS' specifies this string. The initial value of `ORS' is the string `"\n"', i.e. a newline character; thus, normally each `print' statement makes a separate line. You can change how output fields and records are separated by assigning new values to the variables `OFS' and/or `ORS'. The usual place to do this is in the `BEGIN' rule (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.), so that it happens before any input is processed. You may also do this with assignments on the command line, before the names of your input files, or using the `-v' command line option (*note Command Line Options: Options.). The following example prints the first and second fields of each input record separated by a semicolon, with a blank line added after each line: $ awk 'BEGIN { OFS = ";"; ORS = "\n\n" } > { print $1, $2 }' BBS-list -| aardvark;555-5553 -| -| alpo-net;555-3412 -| -| barfly;555-7685 ... If the value of `ORS' does not contain a newline, all your output will be run together on a single line, unless you output newlines some other way.  File: gawk.info, Node: OFMT, Next: Printf, Prev: Output Separators, Up: Printing Controlling Numeric Output with `print' ======================================= When you use the `print' statement to print numeric values, `awk' internally converts the number to a string of characters, and prints that string. `awk' uses the `sprintf' function to do this conversion (*note Built-in Functions for String Manipulation: String Functions.). For now, it suffices to say that the `sprintf' function accepts a "format specification" that tells it how to format numbers (or strings), and that there are a number of different ways in which numbers can be formatted. The different format specifications are discussed more fully in *Note Format-Control Letters: Control Letters. The built-in variable `OFMT' contains the default format specification that `print' uses with `sprintf' when it wants to convert a number to a string for printing. The default value of `OFMT' is `"%.6g"'. By supplying different format specifications as the value of `OFMT', you can change how `print' will print your numbers. As a brief example: $ awk 'BEGIN { > OFMT = "%.0f" # print numbers as integers (rounds) > print 17.23 }' -| 17 According to the POSIX standard, `awk''s behavior will be undefined if `OFMT' contains anything but a floating point conversion specification (d.c.).  File: gawk.info, Node: Printf, Next: Redirection, Prev: OFMT, Up: Printing Using `printf' Statements for Fancier Printing ============================================== If you want more precise control over the output format than `print' gives you, use `printf'. With `printf' you can specify the width to use for each item, and you can specify various formatting choices for numbers (such as what radix to use, whether to print an exponent, whether to print a sign, and how many digits to print after the decimal point). You do this by supplying a string, called the "format string", which controls how and where to print the other arguments. * Menu: * Basic Printf:: Syntax of the `printf' statement. * Control Letters:: Format-control letters. * Format Modifiers:: Format-specification modifiers. * Printf Examples:: Several examples.  File: gawk.info, Node: Basic Printf, Next: Control Letters, Prev: Printf, Up: Printf Introduction to the `printf' Statement -------------------------------------- The `printf' statement looks like this: printf FORMAT, ITEM1, ITEM2, ... The entire list of arguments may optionally be enclosed in parentheses. The parentheses are necessary if any of the item expressions use the `>' relational operator; otherwise it could be confused with a redirection (*note Redirecting Output of `print' and `printf': Redirection.). The difference between `printf' and `print' is the FORMAT argument. This is an expression whose value is taken as a string; it specifies how to output each of the other arguments. It is called the "format string". The format string is very similar to that in the ANSI C library function `printf'. Most of FORMAT is text to be output verbatim. Scattered among this text are "format specifiers", one per item. Each format specifier says to output the next item in the argument list at that place in the format. The `printf' statement does not automatically append a newline to its output. It outputs only what the format string specifies. So if you want a newline, you must include one in the format string. The output separator variables `OFS' and `ORS' have no effect on `printf' statements. For example: BEGIN { ORS = "\nOUCH!\n"; OFS = "!" msg = "Don't Panic!"; printf "%s\n", msg } This program still prints the familiar `Don't Panic!' message.  File: gawk.info, Node: Control Letters, Next: Format Modifiers, Prev: Basic Printf, Up: Printf Format-Control Letters ---------------------- A format specifier starts with the character `%' and ends with a "format-control letter"; it tells the `printf' statement how to output one item. (If you actually want to output a `%', write `%%'.) The format-control letter specifies what kind of value to print. The rest of the format specifier is made up of optional "modifiers" which are parameters to use, such as the field width. Here is a list of the format-control letters: `c' This prints a number as an ASCII character. Thus, `printf "%c", 65' outputs the letter `A'. The output for a string value is the first character of the string. `d' `i' These are equivalent. They both print a decimal integer. The `%i' specification is for compatibility with ANSI C. `e' `E' This prints a number in scientific (exponential) notation. For example, printf "%4.3e\n", 1950 prints `1.950e+03', with a total of four significant figures of which three follow the decimal point. The `4.3' are modifiers, discussed below. `%E' uses `E' instead of `e' in the output. `f' This prints a number in floating point notation. For example, printf "%4.3f", 1950 prints `1950.000', with a total of four significant figures of which three follow the decimal point. The `4.3' are modifiers, discussed below. `g' `G' This prints a number in either scientific notation or floating point notation, whichever uses fewer characters. If the result is printed in scientific notation, `%G' uses `E' instead of `e'. `o' This prints an unsigned octal integer. (In octal, or base-eight notation, the digits run from `0' to `7'; the decimal number eight is represented as `10' in octal.) `s' This prints a string. `x' `X' This prints an unsigned hexadecimal integer. (In hexadecimal, or base-16 notation, the digits are `0' through `9' and `a' through `f'. The hexadecimal digit `f' represents the decimal number 15.) `%X' uses the letters `A' through `F' instead of `a' through `f'. `%' This isn't really a format-control letter, but it does have a meaning when used after a `%': the sequence `%%' outputs one `%'. It does not consume an argument, and it ignores any modifiers. When using the integer format-control letters for values that are outside the range of a C `long' integer, `gawk' will switch to the `%g' format specifier. Other versions of `awk' may print invalid values, or do something else entirely (d.c.).  File: gawk.info, Node: Format Modifiers, Next: Printf Examples, Prev: Control Letters, Up: Printf Modifiers for `printf' Formats ------------------------------ A format specification can also include "modifiers" that can control how much of the item's value is printed and how much space it gets. The modifiers come between the `%' and the format-control letter. In the examples below, we use the bullet symbol "*" to represent spaces in the output. Here are the possible modifiers, in the order in which they may appear: `-' The minus sign, used before the width modifier (see below), says to left-justify the argument within its specified width. Normally the argument is printed right-justified in the specified width. Thus, printf "%-4s", "foo" prints `foo*'. `SPACE' For numeric conversions, prefix positive values with a space, and negative values with a minus sign. `+' The plus sign, used before the width modifier (see below), says to always supply a sign for numeric conversions, even if the data to be formatted is positive. The `+' overrides the space modifier. `#' Use an "alternate form" for certain control letters. For `%o', supply a leading zero. For `%x', and `%X', supply a leading `0x' or `0X' for a non-zero result. For `%e', `%E', and `%f', the result will always contain a decimal point. For `%g', and `%G', trailing zeros are not removed from the result. `0' A leading `0' (zero) acts as a flag, that indicates output should be padded with zeros instead of spaces. This applies even to non-numeric output formats (d.c.). This flag only has an effect when the field width is wider than the value to be printed. `WIDTH' This is a number specifying the desired minimum width of a field. Inserting any number between the `%' sign and the format control character forces the field to be expanded to this width. The default way to do this is to pad with spaces on the left. For example, printf "%4s", "foo" prints `*foo'. The value of WIDTH is a minimum width, not a maximum. If the item value requires more than WIDTH characters, it can be as wide as necessary. Thus, printf "%4s", "foobar" prints `foobar'. Preceding the WIDTH with a minus sign causes the output to be padded with spaces on the right, instead of on the left. `.PREC' This is a number that specifies the precision to use when printing. For the `e', `E', and `f' formats, this specifies the number of digits you want printed to the right of the decimal point. For the `g', and `G' formats, it specifies the maximum number of significant digits. For the `d', `o', `i', `u', `x', and `X' formats, it specifies the minimum number of digits to print. For a string, it specifies the maximum number of characters from the string that should be printed. Thus, printf "%.4s", "foobar" prints `foob'. The C library `printf''s dynamic WIDTH and PREC capability (for example, `"%*.*s"') is supported. Instead of supplying explicit WIDTH and/or PREC values in the format string, you pass them in the argument list. For example: w = 5 p = 3 s = "abcdefg" printf "%*.*s\n", w, p, s is exactly equivalent to s = "abcdefg" printf "%5.3s\n", s Both programs output `**abc'. Earlier versions of `awk' did not support this capability. If you must use such a version, you may simulate this feature by using concatenation to build up the format string, like so: w = 5 p = 3 s = "abcdefg" printf "%" w "." p "s\n", s This is not particularly easy to read, but it does work. C programmers may be used to supplying additional `l' and `h' flags in `printf' format strings. These are not valid in `awk'. Most `awk' implementations silently ignore these flags. If `--lint' is provided on the command line (*note Command Line Options: Options.), `gawk' will warn about their use. If `--posix' is supplied, their use is a fatal error.  File: gawk.info, Node: Printf Examples, Prev: Format Modifiers, Up: Printf Examples Using `printf' ----------------------- Here is how to use `printf' to make an aligned table: awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list prints the names of bulletin boards (`$1') of the file `BBS-list' as a string of 10 characters, left justified. It also prints the phone numbers (`$2') afterward on the line. This produces an aligned two-column table of names and phone numbers: $ awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list -| aardvark 555-5553 -| alpo-net 555-3412 -| barfly 555-7685 -| bites 555-1675 -| camelot 555-0542 -| core 555-2912 -| fooey 555-1234 -| foot 555-6699 -| macfoo 555-6480 -| sdace 555-3430 -| sabafoo 555-2127 Did you notice that we did not specify that the phone numbers be printed as numbers? They had to be printed as strings because the numbers are separated by a dash. If we had tried to print the phone numbers as numbers, all we would have gotten would have been the first three digits, `555'. This would have been pretty confusing. We did not specify a width for the phone numbers because they are the last things on their lines. We don't need to put spaces after them. We could make our table look even nicer by adding headings to the tops of the columns. To do this, we use the `BEGIN' pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.) to force the header to be printed only once, at the beginning of the `awk' program: awk 'BEGIN { print "Name Number" print "---- ------" } { printf "%-10s %s\n", $1, $2 }' BBS-list Did you notice that we mixed `print' and `printf' statements in the above example? We could have used just `printf' statements to get the same results: awk 'BEGIN { printf "%-10s %s\n", "Name", "Number" printf "%-10s %s\n", "----", "------" } { printf "%-10s %s\n", $1, $2 }' BBS-list By printing each column heading with the same format specification used for the elements of the column, we have made sure that the headings are aligned just like the columns. The fact that the same format specification is used three times can be emphasized by storing it in a variable, like this: awk 'BEGIN { format = "%-10s %s\n" printf format, "Name", "Number" printf format, "----", "------" } { printf format, $1, $2 }' BBS-list See if you can use the `printf' statement to line up the headings and table data for our `inventory-shipped' example covered earlier in the section on the `print' statement (*note The `print' Statement: Print.).  File: gawk.info, Node: Redirection, Next: Special Files, Prev: Printf, Up: Printing Redirecting Output of `print' and `printf' ========================================== So far we have been dealing only with output that prints to the standard output, usually your terminal. Both `print' and `printf' can also send their output to other places. This is called "redirection". A redirection appears after the `print' or `printf' statement. Redirections in `awk' are written just like redirections in shell commands, except that they are written inside the `awk' program. There are three forms of output redirection: output to a file, output appended to a file, and output through a pipe to another command. They are all shown for the `print' statement, but they work identically for `printf' also. `print ITEMS > OUTPUT-FILE' This type of redirection prints the items into the output file OUTPUT-FILE. The file name OUTPUT-FILE can be any expression. Its value is changed to a string and then used as a file name (*note Expressions::.). When this type of redirection is used, the OUTPUT-FILE is erased before the first output is written to it. Subsequent writes to the same OUTPUT-FILE do not erase OUTPUT-FILE, but append to it. If OUTPUT-FILE does not exist, then it is created. For example, here is how an `awk' program can write a list of BBS names to a file `name-list' and a list of phone numbers to a file `phone-list'. Each output file contains one name or number per line. $ awk '{ print $2 > "phone-list" > print $1 > "name-list" }' BBS-list $ cat phone-list -| 555-5553 -| 555-3412 ... $ cat name-list -| aardvark -| alpo-net ... `print ITEMS >> OUTPUT-FILE' This type of redirection prints the items into the pre-existing output file OUTPUT-FILE. The difference between this and the single-`>' redirection is that the old contents (if any) of OUTPUT-FILE are not erased. Instead, the `awk' output is appended to the file. If OUTPUT-FILE does not exist, then it is created. `print ITEMS | COMMAND' It is also possible to send output to another program through a pipe instead of into a file. This type of redirection opens a pipe to COMMAND and writes the values of ITEMS through this pipe, to another process created to execute COMMAND. The redirection argument COMMAND is actually an `awk' expression. Its value is converted to a string, whose contents give the shell command to be run. For example, this produces two files, one unsorted list of BBS names and one list sorted in reverse alphabetical order: awk '{ print $1 > "names.unsorted" command = "sort -r > names.sorted" print $1 | command }' BBS-list Here the unsorted list is written with an ordinary redirection while the sorted list is written by piping through the `sort' utility. This example uses redirection to mail a message to a mailing list `bug-system'. This might be useful when trouble is encountered in an `awk' script run periodically for system maintenance. report = "mail bug-system" print "Awk script failed:", $0 | report m = ("at record number " FNR " of " FILENAME) print m | report close(report) The message is built using string concatenation and saved in the variable `m'. It is then sent down the pipeline to the `mail' program. We call the `close' function here because it's a good idea to close the pipe as soon as all the intended output has been sent to it. *Note Closing Input and Output Files and Pipes: Close Files And Pipes, for more information on this. This example also illustrates the use of a variable to represent a FILE or COMMAND: it is not necessary to always use a string constant. Using a variable is generally a good idea, since `awk' requires you to spell the string value identically every time. Redirecting output using `>', `>>', or `|' asks the system to open a file or pipe only if the particular FILE or COMMAND you've specified has not already been written to by your program, or if it has been closed since it was last written to. Many `awk' implementations limit the number of pipelines an `awk' program may have open to just one! In `gawk', there is no such limit. You can open as many pipelines as the underlying operating system will permit.  File: gawk.info, Node: Special Files, Next: Close Files And Pipes, Prev: Redirection, Up: Printing Special File Names in `gawk' ============================ Running programs conventionally have three input and output streams already available to them for reading and writing. These are known as the "standard input", "standard output", and "standard error output". These streams are, by default, connected to your terminal, but they are often redirected with the shell, via the `<', `<<', `>', `>>', `>&' and `|' operators. Standard error is typically used for writing error messages; the reason we have two separate streams, standard output and standard error, is so that they can be redirected separately. In other implementations of `awk', the only way to write an error message to standard error in an `awk' program is as follows: print "Serious error detected!" | "cat 1>&2" This works by opening a pipeline to a shell command which can access the standard error stream which it inherits from the `awk' process. This is far from elegant, and is also inefficient, since it requires a separate process. So people writing `awk' programs often neglect to do this. Instead, they send the error messages to the terminal, like this: print "Serious error detected!" > "/dev/tty" This usually has the same effect, but not always: although the standard error stream is usually the terminal, it can be redirected, and when that happens, writing to the terminal is not correct. In fact, if `awk' is run from a background job, it may not have a terminal at all. Then opening `/dev/tty' will fail. `gawk' provides special file names for accessing the three standard streams. When you redirect input or output in `gawk', if the file name matches one of these special names, then `gawk' directly uses the stream it stands for. `/dev/stdin' The standard input (file descriptor 0). `/dev/stdout' The standard output (file descriptor 1). `/dev/stderr' The standard error output (file descriptor 2). `/dev/fd/N' The file associated with file descriptor N. Such a file must have been opened by the program initiating the `awk' execution (typically the shell). Unless you take special pains in the shell from which you invoke `gawk', only descriptors 0, 1 and 2 are available. The file names `/dev/stdin', `/dev/stdout', and `/dev/stderr' are aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively, but they are more self-explanatory. The proper way to write an error message in a `gawk' program is to use `/dev/stderr', like this: print "Serious error detected!" > "/dev/stderr" `gawk' also provides special file names that give access to information about the running `gawk' process. Each of these "files" provides a single record of information. To read them more than once, you must first close them with the `close' function (*note Closing Input and Output Files and Pipes: Close Files And Pipes.). The filenames are: `/dev/pid' Reading this file returns the process ID of the current process, in decimal, terminated with a newline. `/dev/ppid' Reading this file returns the parent process ID of the current process, in decimal, terminated with a newline. `/dev/pgrpid' Reading this file returns the process group ID of the current process, in decimal, terminated with a newline. `/dev/user' Reading this file returns a single record terminated with a newline. The fields are separated with spaces. The fields represent the following information: `$1' The return value of the `getuid' system call (the real user ID number). `$2' The return value of the `geteuid' system call (the effective user ID number). `$3' The return value of the `getgid' system call (the real group ID number). `$4' The return value of the `getegid' system call (the effective group ID number). If there are any additional fields, they are the group IDs returned by `getgroups' system call. (Multiple groups may not be supported on all systems.) These special file names may be used on the command line as data files, as well as for I/O redirections within an `awk' program. They may not be used as source files with the `-f' option. Recognition of these special file names is disabled if `gawk' is in compatibility mode (*note Command Line Options: Options.). *Caution*: Unless your system actually has a `/dev/fd' directory (or any of the other above listed special files), the interpretation of these file names is done by `gawk' itself. For example, using `/dev/fd/4' for output will actually write on file descriptor 4, and not on a new file descriptor that was `dup''ed from file descriptor 4. Most of the time this does not matter; however, it is important to *not* close any of the files related to file descriptors 0, 1, and 2. If you do close one of these files, unpredictable behavior will result. The special files that provide process-related information may disappear in a future version of `gawk'. *Note Probable Future Extensions: Future Extensions.  File: gawk.info, Node: Close Files And Pipes, Prev: Special Files, Up: Printing Closing Input and Output Files and Pipes ======================================== If the same file name or the same shell command is used with `getline' (*note Explicit Input with `getline': Getline.) more than once during the execution of an `awk' program, the file is opened (or the command is executed) only the first time. At that time, the first record of input is read from that file or command. The next time the same file or command is used in `getline', another record is read from it, and so on. Similarly, when a file or pipe is opened for output, the file name or command associated with it is remembered by `awk' and subsequent writes to the same file or command are appended to the previous writes. The file or pipe stays open until `awk' exits. This implies that if you want to start reading the same file again from the beginning, or if you want to rerun a shell command (rather than reading more output from the command), you must take special steps. What you must do is use the `close' function, as follows: close(FILENAME) or close(COMMAND) The argument FILENAME or COMMAND can be any expression. Its value must *exactly* match the string that was used to open the file or start the command (spaces and other "irrelevant" characters included). For example, if you open a pipe with this: "sort -r names" | getline foo then you must close it with this: close("sort -r names") Once this function call is executed, the next `getline' from that file or command, or the next `print' or `printf' to that file or command, will reopen the file or rerun the command. Because the expression that you use to close a file or pipeline must exactly match the expression used to open the file or run the command, it is good practice to use a variable to store the file name or command. The previous example would become sortcom = "sort -r names" sortcom | getline foo ... close(sortcom) This helps avoid hard-to-find typographical errors in your `awk' programs. Here are some reasons why you might need to close an output file: * To write a file and read it back later on in the same `awk' program. Close the file when you are finished writing it; then you can start reading it with `getline'. * To write numerous files, successively, in the same `awk' program. If you don't close the files, eventually you may exceed a system limit on the number of open files in one process. So close each one when you are finished writing it. * To make a command finish. When you redirect output through a pipe, the command reading the pipe normally continues to try to read input as long as the pipe is open. Often this means the command cannot really do its work until the pipe is closed. For example, if you redirect output to the `mail' program, the message is not actually sent until the pipe is closed. * To run the same program a second time, with the same arguments. This is not the same thing as giving more input to the first run! For example, suppose you pipe output to the `mail' program. If you output several lines redirected to this pipe without closing it, they make a single message of several lines. By contrast, if you close the pipe after each line of output, then each line makes a separate message. `close' returns a value of zero if the close succeeded. Otherwise, the value will be non-zero. In this case, `gawk' sets the variable `ERRNO' to a string describing the error that occurred. If you use more files than the system allows you to have open, `gawk' will attempt to multiplex the available open files among your data files. `gawk''s ability to do this depends upon the facilities of your operating system: it may not always work. It is therefore both good practice and good portability advice to always use `close' on your files when you are done with them.  File: gawk.info, Node: Expressions, Next: Patterns and Actions, Prev: Printing, Up: Top Expressions *********** Expressions are the basic building blocks of `awk' patterns and actions. An expression evaluates to a value, which you can print, test, store in a variable or pass to a function. Additionally, an expression can assign a new value to a variable or a field, with an assignment operator. An expression can serve as a pattern or action statement on its own. Most other kinds of statements contain one or more expressions which specify data on which to operate. As in other languages, expressions in `awk' include variables, array references, constants, and function calls, as well as combinations of these with various operators. * Menu: * Constants:: String, numeric, and regexp constants. * Using Constant Regexps:: When and how to use a regexp constant. * Variables:: Variables give names to values for later use. * Conversion:: The conversion of strings to numbers and vice versa. * Arithmetic Ops:: Arithmetic operations (`+', `-', etc.) * Concatenation:: Concatenating strings. * Assignment Ops:: Changing the value of a variable or a field. * Increment Ops:: Incrementing the numeric value of a variable. * Truth Values:: What is "true" and what is "false". * Typing and Comparison:: How variables acquire types, and how this affects comparison of numbers and strings with `<', etc. * Boolean Ops:: Combining comparison expressions using boolean operators `||' ("or"), `&&' ("and") and `!' ("not"). * Conditional Exp:: Conditional expressions select between two subexpressions under control of a third subexpression. * Function Calls:: A function call is an expression. * Precedence:: How various operators nest.  File: gawk.info, Node: Constants, Next: Using Constant Regexps, Prev: Expressions, Up: Expressions Constant Expressions ==================== The simplest type of expression is the "constant", which always has the same value. There are three types of constants: numeric constants, string constants, and regular expression constants. * Menu: * Scalar Constants:: Numeric and string constants. * Regexp Constants:: Regular Expression constants.  File: gawk.info, Node: Scalar Constants, Next: Regexp Constants, Prev: Constants, Up: Constants Numeric and String Constants ---------------------------- A "numeric constant" stands for a number. This number can be an integer, a decimal fraction, or a number in scientific (exponential) notation.(1) Here are some examples of numeric constants, which all have the same value: 105 1.05e+2 1050e-1 A string constant consists of a sequence of characters enclosed in double-quote marks. For example: "parrot" represents the string whose contents are `parrot'. Strings in `gawk' can be of any length and they can contain any of the possible eight-bit ASCII characters including ASCII NUL (character code zero). Other `awk' implementations may have difficulty with some character codes. ---------- Footnotes ---------- (1) The internal representation uses double-precision floating point numbers. If you don't know what that means, then don't worry about it.  File: gawk.info, Node: Regexp Constants, Prev: Scalar Constants, Up: Constants Regular Expression Constants ---------------------------- A regexp constant is a regular expression description enclosed in slashes, such as `/^beginning and end$/'. Most regexps used in `awk' programs are constant, but the `~' and `!~' matching operators can also match computed or "dynamic" regexps (which are just ordinary strings or variables that contain a regexp).  File: gawk.info, Node: Using Constant Regexps, Next: Variables, Prev: Constants, Up: Expressions Using Regular Expression Constants ================================== When used on the right hand side of the `~' or `!~' operators, a regexp constant merely stands for the regexp that is to be matched. Regexp constants (such as `/foo/') may be used like simple expressions. When a regexp constant appears by itself, it has the same meaning as if it appeared in a pattern, i.e. `($0 ~ /foo/)' (d.c.) (*note Expressions as Patterns: Expression Patterns.). This means that the two code segments, if ($0 ~ /barfly/ || $0 ~ /camelot/) print "found" and if (/barfly/ || /camelot/) print "found" are exactly equivalent. One rather bizarre consequence of this rule is that the following boolean expression is valid, but does not do what the user probably intended: # note that /foo/ is on the left of the ~ if (/foo/ ~ $1) print "found foo" This code is "obviously" testing `$1' for a match against the regexp `/foo/'. But in fact, the expression `/foo/ ~ $1' actually means `($0 ~ /foo/) ~ $1'. In other words, first match the input record against the regexp `/foo/'. The result will be either zero or one, depending upon the success or failure of the match. Then match that result against the first field in the record. Since it is unlikely that you would ever really wish to make this kind of test, `gawk' will issue a warning when it sees this construct in a program. Another consequence of this rule is that the assignment statement matches = /foo/ will assign either zero or one to the variable `matches', depending upon the contents of the current input record. This feature of the language was never well documented until the POSIX specification. Constant regular expressions are also used as the first argument for the `gensub', `sub' and `gsub' functions, and as the second argument of the `match' function (*note Built-in Functions for String Manipulation: String Functions.). Modern implementations of `awk', including `gawk', allow the third argument of `split' to be a regexp constant, while some older implementations do not (d.c.). This can lead to confusion when attempting to use regexp constants as arguments to user defined functions (*note User-defined Functions: User-defined.). For example: function mysub(pat, repl, str, global) { if (global) gsub(pat, repl, str) else sub(pat, repl, str) return str } { ... text = "hi! hi yourself!" mysub(/hi/, "howdy", text, 1) ... } In this example, the programmer wishes to pass a regexp constant to the user-defined function `mysub', which will in turn pass it on to either `sub' or `gsub'. However, what really happens is that the `pat' parameter will be either one or zero, depending upon whether or not `$0' matches `/hi/'. As it is unlikely that you would ever really wish to pass a truth value in this way, `gawk' will issue a warning when it sees a regexp constant used as a parameter to a user-defined function.  File: gawk.info, Node: Variables, Next: Conversion, Prev: Using Constant Regexps, Up: Expressions Variables ========= Variables are ways of storing values at one point in your program for use later in another part of your program. You can manipulate them entirely within your program text, and you can also assign values to them on the `awk' command line. * Menu: * Using Variables:: Using variables in your programs. * Assignment Options:: Setting variables on the command line and a summary of command line syntax. This is an advanced method of input.  File: gawk.info, Node: Using Variables, Next: Assignment Options, Prev: Variables, Up: Variables Using Variables in a Program ---------------------------- Variables let you give names to values and refer to them later. You have already seen variables in many of the examples. The name of a variable must be a sequence of letters, digits and underscores, but it may not begin with a digit. Case is significant in variable names; `a' and `A' are distinct variables. A variable name is a valid expression by itself; it represents the variable's current value. Variables are given new values with "assignment operators", "increment operators" and "decrement operators". *Note Assignment Expressions: Assignment Ops. A few variables have special built-in meanings, such as `FS', the field separator, and `NF', the number of fields in the current input record. *Note Built-in Variables::, for a list of them. These built-in variables can be used and assigned just like all other variables, but their values are also used or changed automatically by `awk'. All built-in variables names are entirely upper-case. Variables in `awk' can be assigned either numeric or string values. By default, variables are initialized to the empty string, which is zero if converted to a number. There is no need to "initialize" each variable explicitly in `awk', the way you would in C and in most other traditional languages.  File: gawk.info, Node: Assignment Options, Prev: Using Variables, Up: Variables Assigning Variables on the Command Line --------------------------------------- You can set any `awk' variable by including a "variable assignment" among the arguments on the command line when you invoke `awk' (*note Other Command Line Arguments: Other Arguments.). Such an assignment has this form: VARIABLE=TEXT With it, you can set a variable either at the beginning of the `awk' run or in between input files. If you precede the assignment with the `-v' option, like this: -v VARIABLE=TEXT then the variable is set at the very beginning, before even the `BEGIN' rules are run. The `-v' option and its assignment must precede all the file name arguments, as well as the program text. (*Note Command Line Options: Options, for more information about the `-v' option.) Otherwise, the variable assignment is performed at a time determined by its position among the input file arguments: after the processing of the preceding input file argument. For example: awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list prints the value of field number `n' for all input records. Before the first file is read, the command line sets the variable `n' equal to four. This causes the fourth field to be printed in lines from the file `inventory-shipped'. After the first file has finished, but before the second file is started, `n' is set to two, so that the second field is printed in lines from `BBS-list'. $ awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list -| 15 -| 24 ... -| 555-5553 -| 555-3412 ... Command line arguments are made available for explicit examination by the `awk' program in an array named `ARGV' (*note Using `ARGC' and `ARGV': ARGC and ARGV.). `awk' processes the values of command line assignments for escape sequences (d.c.) (*note Escape Sequences::.).  File: gawk.info, Node: Conversion, Next: Arithmetic Ops, Prev: Variables, Up: Expressions Conversion of Strings and Numbers ================================= Strings are converted to numbers, and numbers to strings, if the context of the `awk' program demands it. For example, if the value of either `foo' or `bar' in the expression `foo + bar' happens to be a string, it is converted to a number before the addition is performed. If numeric values appear in string concatenation, they are converted to strings. Consider this: two = 2; three = 3 print (two three) + 4 This prints the (numeric) value 27. The numeric values of the variables `two' and `three' are converted to strings and concatenated together, and the resulting string is converted back to the number 23, to which four is then added. If, for some reason, you need to force a number to be converted to a string, concatenate the empty string, `""', with that number. To force a string to be converted to a number, add zero to that string. A string is converted to a number by interpreting any numeric prefix of the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to 1000, and `"25fix"' has a numeric value of 25. Strings that can't be interpreted as valid numbers are converted to zero. The exact manner in which numbers are converted into strings is controlled by the `awk' built-in variable `CONVFMT' (*note Built-in Variables::.). Numbers are converted using the `sprintf' function (*note Built-in Functions for String Manipulation: String Functions.) with `CONVFMT' as the format specifier. `CONVFMT''s default value is `"%.6g"', which prints a value with at least six significant digits. For some applications you will want to change it to specify more precision. Double precision on most modern machines gives you 16 or 17 decimal digits of precision. Strange results can happen if you set `CONVFMT' to a string that doesn't tell `sprintf' how to format floating point numbers in a useful way. For example, if you forget the `%' in the format, all numbers will be converted to the same constant string. As a special case, if a number is an integer, then the result of converting it to a string is *always* an integer, no matter what the value of `CONVFMT' may be. Given the following code fragment: CONVFMT = "%2.2f" a = 12 b = a "" `b' has the value `"12"', not `"12.00"' (d.c.). Prior to the POSIX standard, `awk' specified that the value of `OFMT' was used for converting numbers to strings. `OFMT' specifies the output format to use when printing numbers with `print'. `CONVFMT' was introduced in order to separate the semantics of conversion from the semantics of printing. Both `CONVFMT' and `OFMT' have the same default value: `"%.6g"'. In the vast majority of cases, old `awk' programs will not change their behavior. However, this use of `OFMT' is something to keep in mind if you must port your program to other implementations of `awk'; we recommend that instead of changing your programs, you just port `gawk' itself! *Note The `print' Statement: Print, for more information on the `print' statement.  File: gawk.info, Node: Arithmetic Ops, Next: Concatenation, Prev: Conversion, Up: Expressions Arithmetic Operators ==================== The `awk' language uses the common arithmetic operators when evaluating expressions. All of these arithmetic operators follow normal precedence rules, and work as you would expect them to. Here is a file `grades' containing a list of student names and three test scores per student (it's a small class): Pat 100 97 58 Sandy 84 72 93 Chris 72 92 89 This programs takes the file `grades', and prints the average of the scores. $ awk '{ sum = $2 + $3 + $4 ; avg = sum / 3 > print $1, avg }' grades -| Pat 85 -| Sandy 83 -| Chris 84.3333 This table lists the arithmetic operators in `awk', in order from highest precedence to lowest: `- X' Negation. `+ X' Unary plus. The expression is converted to a number. `X ^ Y' `X ** Y' Exponentiation: X raised to the Y power. `2 ^ 3' has the value eight. The character sequence `**' is equivalent to `^'. (The POSIX standard only specifies the use of `^' for exponentiation.) `X * Y' Multiplication. `X / Y' Division. Since all numbers in `awk' are real numbers, the result is not rounded to an integer: `3 / 4' has the value 0.75. `X % Y' Remainder. The quotient is rounded toward zero to an integer, multiplied by Y and this result is subtracted from X. This operation is sometimes known as "trunc-mod." The following relation always holds: b * int(a / b) + (a % b) == a One possibly undesirable effect of this definition of remainder is that `X % Y' is negative if X is negative. Thus, -17 % 8 = -1 In other `awk' implementations, the signedness of the remainder may be machine dependent. `X + Y' Addition. `X - Y' Subtraction. For maximum portability, do not use the `**' operator. Unary plus and minus have the same precedence, the multiplication operators all have the same precedence, and addition and subtraction have the same precedence.  File: gawk.info, Node: Concatenation, Next: Assignment Ops, Prev: Arithmetic Ops, Up: Expressions String Concatenation ==================== It seemed like a good idea at the time. Brian Kernighan There is only one string operation: concatenation. It does not have a specific operator to represent it. Instead, concatenation is performed by writing expressions next to one another, with no operator. For example: $ awk '{ print "Field number one: " $1 }' BBS-list -| Field number one: aardvark -| Field number one: alpo-net ... Without the space in the string constant after the `:', the line would run together. For example: $ awk '{ print "Field number one:" $1 }' BBS-list -| Field number one:aardvark -| Field number one:alpo-net ... Since string concatenation does not have an explicit operator, it is often necessary to insure that it happens where you want it to by using parentheses to enclose the items to be concatenated. For example, the following code fragment does not concatenate `file' and `name' as you might expect: file = "file" name = "name" print "something meaningful" > file name It is necessary to use the following: print "something meaningful" > (file name) We recommend that you use parentheses around concatenation in all but the most common contexts (such as on the right-hand side of `=').  File: gawk.info, Node: Assignment Ops, Next: Increment Ops, Prev: Concatenation, Up: Expressions Assignment Expressions ====================== An "assignment" is an expression that stores a new value into a variable. For example, let's assign the value one to the variable `z': z = 1 After this expression is executed, the variable `z' has the value one. Whatever old value `z' had before the assignment is forgotten. Assignments can store string values also. For example, this would store the value `"this food is good"' in the variable `message': thing = "food" predicate = "good" message = "this " thing " is " predicate (This also illustrates string concatenation.) The `=' sign is called an "assignment operator". It is the simplest assignment operator because the value of the right-hand operand is stored unchanged. Most operators (addition, concatenation, and so on) have no effect except to compute a value. If you ignore the value, you might as well not use the operator. An assignment operator is different; it does produce a value, but even if you ignore the value, the assignment still makes itself felt through the alteration of the variable. We call this a "side effect". The left-hand operand of an assignment need not be a variable (*note Variables::.); it can also be a field (*note Changing the Contents of a Field: Changing Fields.) or an array element (*note Arrays in `awk': Arrays.). These are all called "lvalues", which means they can appear on the left-hand side of an assignment operator. The right-hand operand may be any expression; it produces the new value which the assignment stores in the specified variable, field or array element. (Such values are called "rvalues"). It is important to note that variables do *not* have permanent types. The type of a variable is simply the type of whatever value it happens to hold at the moment. In the following program fragment, the variable `foo' has a numeric value at first, and a string value later on: foo = 1 print foo foo = "bar" print foo When the second assignment gives `foo' a string value, the fact that it previously had a numeric value is forgotten. String values that do not begin with a digit have a numeric value of zero. After executing this code, the value of `foo' is five: foo = "a string" foo = foo + 5 (Note that using a variable as a number and then later as a string can be confusing and is poor programming style. The above examples illustrate how `awk' works, *not* how you should write your own programs!) An assignment is an expression, so it has a value: the same value that is assigned. Thus, `z = 1' as an expression has the value one. One consequence of this is that you can write multiple assignments together: x = y = z = 0 stores the value zero in all three variables. It does this because the value of `z = 0', which is zero, is stored into `y', and then the value of `y = z = 0', which is zero, is stored into `x'. You can use an assignment anywhere an expression is called for. For example, it is valid to write `x != (y = 1)' to set `y' to one and then test whether `x' equals one. But this style tends to make programs hard to read; except in a one-shot program, you should not use such nesting of assignments. Aside from `=', there are several other assignment operators that do arithmetic with the old value of the variable. For example, the operator `+=' computes a new value by adding the right-hand value to the old value of the variable. Thus, the following assignment adds five to the value of `foo': foo += 5 This is equivalent to the following: foo = foo + 5 Use whichever one makes the meaning of your program clearer. There are situations where using `+=' (or any assignment operator) is *not* the same as simply repeating the left-hand operand in the right-hand expression. For example: # Thanks to Pat Rankin for this example BEGIN { foo[rand()] += 5 for (x in foo) print x, foo[x] bar[rand()] = bar[rand()] + 5 for (x in bar) print x, bar[x] } The indices of `bar' are guaranteed to be different, because `rand' will return different values each time it is called. (Arrays and the `rand' function haven't been covered yet. *Note Arrays in `awk': Arrays, and see *Note Numeric Built-in Functions: Numeric Functions, for more information). This example illustrates an important fact about the assignment operators: the left-hand expression is only evaluated *once*. It is also up to the implementation as to which expression is evaluated first, the left-hand one or the right-hand one. Consider this example: i = 1 a[i += 2] = i + 1 The value of `a[3]' could be either two or four. Here is a table of the arithmetic assignment operators. In each case, the right-hand operand is an expression whose value is converted to a number. `LVALUE += INCREMENT' Adds INCREMENT to the value of LVALUE to make the new value of LVALUE. `LVALUE -= DECREMENT' Subtracts DECREMENT from the value of LVALUE. `LVALUE *= COEFFICIENT' Multiplies the value of LVALUE by COEFFICIENT. `LVALUE /= DIVISOR' Divides the value of LVALUE by DIVISOR. `LVALUE %= MODULUS' Sets LVALUE to its remainder by MODULUS. `LVALUE ^= POWER' `LVALUE **= POWER' Raises LVALUE to the power POWER. (Only the `^=' operator is specified by POSIX.) For maximum portability, do not use the `**=' operator.  File: gawk.info, Node: Increment Ops, Next: Truth Values, Prev: Assignment Ops, Up: Expressions Increment and Decrement Operators ================================= "Increment" and "decrement operators" increase or decrease the value of a variable by one. You could do the same thing with an assignment operator, so the increment operators add no power to the `awk' language; but they are convenient abbreviations for very common operations. The operator to add one is written `++'. It can be used to increment a variable either before or after taking its value. To pre-increment a variable V, write `++V'. This adds one to the value of V and that new value is also the value of this expression. The assignment expression `V += 1' is completely equivalent. Writing the `++' after the variable specifies post-increment. This increments the variable value just the same; the difference is that the value of the increment expression itself is the variable's *old* value. Thus, if `foo' has the value four, then the expression `foo++' has the value four, but it changes the value of `foo' to five. The post-increment `foo++' is nearly equivalent to writing `(foo += 1) - 1'. It is not perfectly equivalent because all numbers in `awk' are floating point: in floating point, `foo + 1 - 1' does not necessarily equal `foo'. But the difference is minute as long as you stick to numbers that are fairly small (less than 10e12). Any lvalue can be incremented. Fields and array elements are incremented just like variables. (Use `$(i++)' when you wish to do a field reference and a variable increment at the same time. The parentheses are necessary because of the precedence of the field reference operator, `$'.) The decrement operator `--' works just like `++' except that it subtracts one instead of adding. Like `++', it can be used before the lvalue to pre-decrement or after it to post-decrement. Here is a summary of increment and decrement expressions. `++LVALUE' This expression increments LVALUE and the new value becomes the value of the expression. `LVALUE++' This expression increments LVALUE, but the value of the expression is the *old* value of LVALUE. `--LVALUE' Like `++LVALUE', but instead of adding, it subtracts. It decrements LVALUE and delivers the value that results. `LVALUE--' Like `LVALUE++', but instead of adding, it subtracts. It decrements LVALUE. The value of the expression is the *old* value of LVALUE.  File: gawk.info, Node: Truth Values, Next: Typing and Comparison, Prev: Increment Ops, Up: Expressions True and False in `awk' ======================= Many programming languages have a special representation for the concepts of "true" and "false." Such languages usually use the special constants `true' and `false', or perhaps their upper-case equivalents. `awk' is different. It borrows a very simple concept of true and false from C. In `awk', any non-zero numeric value, *or* any non-empty string value is true. Any other value (zero or the null string, `""') is false. The following program will print `A strange truth value' three times: BEGIN { if (3.1415927) print "A strange truth value" if ("Four Score And Seven Years Ago") print "A strange truth value" if (j = 57) print "A strange truth value" } There is a surprising consequence of the "non-zero or non-null" rule: The string constant `"0"' is actually true, since it is non-null (d.c.).  File: gawk.info, Node: Typing and Comparison, Next: Boolean Ops, Prev: Truth Values, Up: Expressions Variable Typing and Comparison Expressions ========================================== The Guide is definitive. Reality is frequently inaccurate. The Hitchhiker's Guide to the Galaxy Unlike other programming languages, `awk' variables do not have a fixed type. Instead, they can be either a number or a string, depending upon the value that is assigned to them. The 1992 POSIX standard introduced the concept of a "numeric string", which is simply a string that looks like a number, for example, `" +2"'. This concept is used for determining the type of a variable. The type of the variable is important, since the types of two variables determine how they are compared. In `gawk', variable typing follows these rules. 1. A numeric literal or the result of a numeric operation has the NUMERIC attribute. 2. A string literal or the result of a string operation has the STRING attribute. 3. Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON' elements and the elements of an array created by `split' that are numeric strings have the STRNUM attribute. Otherwise, they have the STRING attribute. Uninitialized variables also have the STRNUM attribute. 4. Attributes propagate across assignments, but are not changed by any use. The last rule is particularly important. In the following program, `a' has numeric type, even though it is later used in a string operation. BEGIN { a = 12.345 b = a " is a cute number" print b } When two operands are compared, either string comparison or numeric comparison may be used, depending on the attributes of the operands, according to the following, symmetric, matrix: +---------------------------------------------- | STRING NUMERIC STRNUM --------+---------------------------------------------- | STRING | string string string | NUMERIC | string numeric numeric | STRNUM | string numeric numeric --------+---------------------------------------------- The basic idea is that user input that looks numeric, and *only* user input, should be treated as numeric, even though it is actually made of characters, and is therefore also a string. "Comparison expressions" compare strings or numbers for relationships such as equality. They are written using "relational operators", which are a superset of those in C. Here is a table of them: `X < Y' True if X is less than Y. `X <= Y' True if X is less than or equal to Y. `X > Y' True if X is greater than Y. `X >= Y' True if X is greater than or equal to Y. `X == Y' True if X is equal to Y. `X != Y' True if X is not equal to Y. `X ~ Y' True if the string X matches the regexp denoted by Y. `X !~ Y' True if the string X does not match the regexp denoted by Y. `SUBSCRIPT in ARRAY' True if the array ARRAY has an element with the subscript SUBSCRIPT. Comparison expressions have the value one if true and zero if false. When comparing operands of mixed types, numeric operands are converted to strings using the value of `CONVFMT' (*note Conversion of Strings and Numbers: Conversion.). Strings are compared by comparing the first character of each, then the second character of each, and so on. Thus `"10"' is less than `"9"'. If there are two strings where one is a prefix of the other, the shorter string is less than the longer one. Thus `"abc"' is less than `"abcd"'. It is very easy to accidentally mistype the `==' operator, and leave off one of the `='s. The result is still valid `awk' code, but the program will not do what you mean: if (a = b) # oops! should be a == b ... else ... Unless `b' happens to be zero or the null string, the `if' part of the test will always succeed. Because the operators are so similar, this kind of error is very difficult to spot when scanning the source code. Here are some sample expressions, how `gawk' compares them, and what the result of the comparison is. `1.5 <= 2.0' numeric comparison (true) `"abc" >= "xyz"' string comparison (false) `1.5 != " +2"' string comparison (true) `"1e2" < "3"' string comparison (true) `a = 2; b = "2"' `a == b' string comparison (true) `a = 2; b = " +2"' `a == b' string comparison (false) In this example, $ echo 1e2 3 | awk '{ print ($1 < $2) ? "true" : "false" }' -| false the result is `false' since both `$1' and `$2' are numeric strings and thus both have the STRNUM attribute, dictating a numeric comparison. The purpose of the comparison rules and the use of numeric strings is to attempt to produce the behavior that is "least surprising," while still "doing the right thing." String comparisons and regular expression comparisons are very different. For example, x == "foo" has the value of one, or is true, if the variable `x' is precisely `foo'. By contrast, x ~ /foo/ has the value one if `x' contains `foo', such as `"Oh, what a fool am I!"'. The right hand operand of the `~' and `!~' operators may be either a regexp constant (`/.../'), or an ordinary expression, in which case the value of the expression as a string is used as a dynamic regexp (*note How to Use Regular Expressions: Regexp Usage.; also *note Using Dynamic Regexps: Computed Regexps.). In recent implementations of `awk', a constant regular expression in slashes by itself is also an expression. The regexp `/REGEXP/' is an abbreviation for this comparison expression: $0 ~ /REGEXP/ One special place where `/foo/' is *not* an abbreviation for `$0 ~ /foo/' is when it is the right-hand operand of `~' or `!~'! *Note Using Regular Expression Constants: Using Constant Regexps, where this is discussed in more detail.  File: gawk.info, Node: Boolean Ops, Next: Conditional Exp, Prev: Typing and Comparison, Up: Expressions Boolean Expressions =================== A "boolean expression" is a combination of comparison expressions or matching expressions, using the boolean operators "or" (`||'), "and" (`&&'), and "not" (`!'), along with parentheses to control nesting. The truth value of the boolean expression is computed by combining the truth values of the component expressions. Boolean expressions are also referred to as "logical expressions". The terms are equivalent. Boolean expressions can be used wherever comparison and matching expressions can be used. They can be used in `if', `while', `do' and `for' statements (*note Control Statements in Actions: Statements.). They have numeric values (one if true, zero if false), which come into play if the result of the boolean expression is stored in a variable, or used in arithmetic. In addition, every boolean expression is also a valid pattern, so you can use one as a pattern to control the execution of rules. Here are descriptions of the three boolean operators, with examples. `BOOLEAN1 && BOOLEAN2' True if both BOOLEAN1 and BOOLEAN2 are true. For example, the following statement prints the current input record if it contains both `2400' and `foo'. if ($0 ~ /2400/ && $0 ~ /foo/) print The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is true. This can make a difference when BOOLEAN2 contains expressions that have side effects: in the case of `$0 ~ /foo/ && ($2 == bar++)', the variable `bar' is not incremented if there is no `foo' in the record. `BOOLEAN1 || BOOLEAN2' True if at least one of BOOLEAN1 or BOOLEAN2 is true. For example, the following statement prints all records in the input that contain *either* `2400' or `foo', or both. if ($0 ~ /2400/ || $0 ~ /foo/) print The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is false. This can make a difference when BOOLEAN2 contains expressions that have side effects. `! BOOLEAN' True if BOOLEAN is false. For example, the following program prints all records in the input file `BBS-list' that do *not* contain the string `foo'. awk '{ if (! ($0 ~ /foo/)) print }' BBS-list The `&&' and `||' operators are called "short-circuit" operators because of the way they work. Evaluation of the full expression is "short-circuited" if the result can be determined part way through its evaluation. You can continue a statement that uses `&&' or `||' simply by putting a newline after them. But you cannot put a newline in front of either of these operators without using backslash continuation (*note `awk' Statements Versus Lines: Statements/Lines.). The actual value of an expression using the `!' operator will be either one or zero, depending upon the truth value of the expression it is applied to. The `!' operator is often useful for changing the sense of a flag variable from false to true and back again. For example, the following program is one way to print lines in between special bracketing lines: $1 == "START" { interested = ! interested } interested == 1 { print } $1 == "END" { interested = ! interested } The variable `interested', like all `awk' variables, starts out initialized to zero, which is also false. When a line is seen whose first field is `START', the value of `interested' is toggled to true, using `!'. The next rule prints lines as long as `interested' is true. When a line is seen whose first field is `END', `interested' is toggled back to false.  File: gawk.info, Node: Conditional Exp, Next: Function Calls, Prev: Boolean Ops, Up: Expressions Conditional Expressions ======================= A "conditional expression" is a special kind of expression with three operands. It allows you to use one expression's value to select one of two other expressions. The conditional expression is the same as in the C language: SELECTOR ? IF-TRUE-EXP : IF-FALSE-EXP There are three subexpressions. The first, SELECTOR, is always computed first. If it is "true" (not zero and not null) then IF-TRUE-EXP is computed next and its value becomes the value of the whole expression. Otherwise, IF-FALSE-EXP is computed next and its value becomes the value of the whole expression. For example, this expression produces the absolute value of `x': x > 0 ? x : -x Each time the conditional expression is computed, exactly one of IF-TRUE-EXP and IF-FALSE-EXP is computed; the other is ignored. This is important when the expressions contain side effects. For example, this conditional expression examines element `i' of either array `a' or array `b', and increments `i'. x == y ? a[i++] : b[i++] This is guaranteed to increment `i' exactly once, because each time only one of the two increment expressions is executed, and the other is not. *Note Arrays in `awk': Arrays, for more information about arrays. As a minor `gawk' extension, you can continue a statement that uses `?:' simply by putting a newline after either character. However, you cannot put a newline in front of either character without using backslash continuation (*note `awk' Statements Versus Lines: Statements/Lines.).  File: gawk.info, Node: Function Calls, Next: Precedence, Prev: Conditional Exp, Up: Expressions Function Calls ============== A "function" is a name for a particular calculation. Because it has a name, you can ask for it by name at any point in the program. For example, the function `sqrt' computes the square root of a number. A fixed set of functions are "built-in", which means they are available in every `awk' program. The `sqrt' function is one of these. *Note Built-in Functions: Built-in, for a list of built-in functions and their descriptions. In addition, you can define your own functions for use in your program. *Note User-defined Functions: User-defined, for how to do this. The way to use a function is with a "function call" expression, which consists of the function name followed immediately by a list of "arguments" in parentheses. The arguments are expressions which provide the raw materials for the function's calculations. When there is more than one argument, they are separated by commas. If there are no arguments, write just `()' after the function name. Here are some examples: sqrt(x^2 + y^2) one argument atan2(y, x) two arguments rand() no arguments *Do not put any space between the function name and the open-parenthesis!* A user-defined function name looks just like the name of a variable, and space would make the expression look like concatenation of a variable with an expression inside parentheses. Space before the parenthesis is harmless with built-in functions, but it is best not to get into the habit of using space to avoid mistakes with user-defined functions. Each function expects a particular number of arguments. For example, the `sqrt' function must be called with a single argument, the number to take the square root of: sqrt(ARGUMENT) Some of the built-in functions allow you to omit the final argument. If you do so, they use a reasonable default. *Note Built-in Functions: Built-in, for full details. If arguments are omitted in calls to user-defined functions, then those arguments are treated as local variables, initialized to the empty string (*note User-defined Functions: User-defined.). Like every other expression, the function call has a value, which is computed by the function based on the arguments you give it. In this example, the value of `sqrt(ARGUMENT)' is the square root of ARGUMENT. A function can also have side effects, such as assigning values to certain variables or doing I/O. Here is a command to read numbers, one number per line, and print the square root of each one: $ awk '{ print "The square root of", $1, "is", sqrt($1) }' 1 -| The square root of 1 is 1 3 -| The square root of 3 is 1.73205 5 -| The square root of 5 is 2.23607 Control-d  File: gawk.info, Node: Precedence, Prev: Function Calls, Up: Expressions Operator Precedence (How Operators Nest) ======================================== "Operator precedence" determines how operators are grouped, when different operators appear close by in one expression. For example, `*' has higher precedence than `+'; thus, `a + b * c' means to multiply `b' and `c', and then add `a' to the product (i.e. `a + (b * c)'). You can overrule the precedence of the operators by using parentheses. You can think of the precedence rules as saying where the parentheses are assumed to be if you do not write parentheses yourself. In fact, it is wise to always use parentheses whenever you have an unusual combination of operators, because other people who read the program may not remember what the precedence is in this case. You might forget, too; then you could make a mistake. Explicit parentheses will help prevent any such mistake. When operators of equal precedence are used together, the leftmost operator groups first, except for the assignment, conditional and exponentiation operators, which group in the opposite order. Thus, `a - b + c' groups as `(a - b) + c', and `a = b = c' groups as `a = (b = c)'. The precedence of prefix unary operators does not matter as long as only unary operators are involved, because there is only one way to interpret them--innermost first. Thus, `$++i' means `$(++i)' and `++$x' means `++($x)'. However, when another operator follows the operand, then the precedence of the unary operators can matter. Thus, `$x^2' means `($x)^2', but `-x^2' means `-(x^2)', because `-' has lower precedence than `^' while `$' has higher precedence. Here is a table of `awk''s operators, in order from highest precedence to lowest: `(...)' Grouping. `$' Field. `++ --' Increment, decrement. `^ **' Exponentiation. These operators group right-to-left. (The `**' operator is not specified by POSIX.) `+ - !' Unary plus, minus, logical "not". `* / %' Multiplication, division, modulus. `+ -' Addition, subtraction. `Concatenation' No special token is used to indicate concatenation. The operands are simply written side by side. `< <= == !=' `> >= >> |' Relational, and redirection. The relational operators and the redirections have the same precedence level. Characters such as `>' serve both as relationals and as redirections; the context distinguishes between the two meanings. Note that the I/O redirection operators in `print' and `printf' statements belong to the statement level, not to expressions. The redirection does not produce an expression which could be the operand of another operator. As a result, it does not make sense to use a redirection operator near another operator of lower precedence, without parentheses. Such combinations, for example `print foo > a ? b : c', result in syntax errors. The correct way to write this statement is `print foo > (a ? b : c)'. `~ !~' Matching, non-matching. `in' Array membership. `&&' Logical "and". `||' Logical "or". `?:' Conditional. This operator groups right-to-left. `= += -= *=' `/= %= ^= **=' Assignment. These operators group right-to-left. (The `**=' operator is not specified by POSIX.)  File: gawk.info, Node: Patterns and Actions, Next: Statements, Prev: Expressions, Up: Top Patterns and Actions ******************** As you have already seen, each `awk' statement consists of a pattern with an associated action. This chapter describes how you build patterns and actions. * Menu: * Pattern Overview:: What goes into a pattern. * Action Overview:: What goes into an action.  File: gawk.info, Node: Pattern Overview, Next: Action Overview, Prev: Patterns and Actions, Up: Patterns and Actions Pattern Elements ================ Patterns in `awk' control the execution of rules: a rule is executed when its pattern matches the current input record. This section explains all about how to write patterns. * Menu: * Kinds of Patterns:: A list of all kinds of patterns. * Regexp Patterns:: Using regexps as patterns. * Expression Patterns:: Any expression can be used as a pattern. * Ranges:: Pairs of patterns specify record ranges. * BEGIN/END:: Specifying initialization and cleanup rules. * Empty:: The empty pattern, which matches every record.  File: gawk.info, Node: Kinds of Patterns, Next: Regexp Patterns, Prev: Pattern Overview, Up: Pattern Overview Kinds of Patterns ----------------- Here is a summary of the types of patterns supported in `awk'. `/REGULAR EXPRESSION/' A regular expression as a pattern. It matches when the text of the input record fits the regular expression. (*Note Regular Expressions: Regexp.) `EXPRESSION' A single expression. It matches when its value is non-zero (if a number) or non-null (if a string). (*Note Expressions as Patterns: Expression Patterns.) `PAT1, PAT2' A pair of patterns separated by a comma, specifying a range of records. The range includes both the initial record that matches PAT1, and the final record that matches PAT2. (*Note Specifying Record Ranges with Patterns: Ranges.) `BEGIN' `END' Special patterns for you to supply start-up or clean-up actions for your `awk' program. (*Note The `BEGIN' and `END' Special Patterns: BEGIN/END.) `EMPTY' The empty pattern matches every input record. (*Note The Empty Pattern: Empty.)  File: gawk.info, Node: Regexp Patterns, Next: Expression Patterns, Prev: Kinds of Patterns, Up: Pattern Overview Regular Expressions as Patterns ------------------------------- We have been using regular expressions as patterns since our early examples. This kind of pattern is simply a regexp constant in the pattern part of a rule. Its meaning is `$0 ~ /PATTERN/'. The pattern matches when the input record matches the regexp. For example: /foo|bar|baz/ { buzzwords++ } END { print buzzwords, "buzzwords seen" }  File: gawk.info, Node: Expression Patterns, Next: Ranges, Prev: Regexp Patterns, Up: Pattern Overview Expressions as Patterns ----------------------- Any `awk' expression is valid as an `awk' pattern. Then the pattern matches if the expression's value is non-zero (if a number) or non-null (if a string). The expression is reevaluated each time the rule is tested against a new input record. If the expression uses fields such as `$1', the value depends directly on the new input record's text; otherwise, it depends only on what has happened so far in the execution of the `awk' program, but that may still be useful. A very common kind of expression used as a pattern is the comparison expression, using the comparison operators described in *Note Variable Typing and Comparison Expressions: Typing and Comparison. Regexp matching and non-matching are also very common expressions. The left operand of the `~' and `!~' operators is a string. The right operand is either a constant regular expression enclosed in slashes (`/REGEXP/'), or any expression, whose string value is used as a dynamic regular expression (*note Using Dynamic Regexps: Computed Regexps.). The following example prints the second field of each input record whose first field is precisely `foo'. $ awk '$1 == "foo" { print $2 }' BBS-list (There is no output, since there is no BBS site named "foo".) Contrast this with the following regular expression match, which would accept any record with a first field that contains `foo': $ awk '$1 ~ /foo/ { print $2 }' BBS-list -| 555-1234 -| 555-6699 -| 555-6480 -| 555-2127 Boolean expressions are also commonly used as patterns. Whether the pattern matches an input record depends on whether its subexpressions match. For example, the following command prints all records in `BBS-list' that contain both `2400' and `foo'. $ awk '/2400/ && /foo/' BBS-list -| fooey 555-1234 2400/1200/300 B The following command prints all records in `BBS-list' that contain *either* `2400' or `foo', or both. $ awk '/2400/ || /foo/' BBS-list -| alpo-net 555-3412 2400/1200/300 A -| bites 555-1675 2400/1200/300 A -| fooey 555-1234 2400/1200/300 B -| foot 555-6699 1200/300 B -| macfoo 555-6480 1200/300 A -| sdace 555-3430 2400/1200/300 A -| sabafoo 555-2127 1200/300 C The following command prints all records in `BBS-list' that do *not* contain the string `foo'. $ awk '! /foo/' BBS-list -| aardvark 555-5553 1200/300 B -| alpo-net 555-3412 2400/1200/300 A -| barfly 555-7685 1200/300 A -| bites 555-1675 2400/1200/300 A -| camelot 555-0542 300 C -| core 555-2912 1200/300 C -| sdace 555-3430 2400/1200/300 A The subexpressions of a boolean operator in a pattern can be constant regular expressions, comparisons, or any other `awk' expressions. Range patterns are not expressions, so they cannot appear inside boolean patterns. Likewise, the special patterns `BEGIN' and `END', which never match any input record, are not expressions and cannot appear inside boolean patterns. A regexp constant as a pattern is also a special case of an expression pattern. `/foo/' as an expression has the value one if `foo' appears in the current input record; thus, as a pattern, `/foo/' matches any record containing `foo'.  File: gawk.info, Node: Ranges, Next: BEGIN/END, Prev: Expression Patterns, Up: Pattern Overview Specifying Record Ranges with Patterns -------------------------------------- A "range pattern" is made of two patterns separated by a comma, of the form `BEGPAT, ENDPAT'. It matches ranges of consecutive input records. The first pattern, BEGPAT, controls where the range begins, and the second one, ENDPAT, controls where it ends. For example, awk '$1 == "on", $1 == "off"' prints every record between `on'/`off' pairs, inclusive. A range pattern starts out by matching BEGPAT against every input record; when a record matches BEGPAT, the range pattern becomes "turned on". The range pattern matches this record. As long as it stays turned on, it automatically matches every input record read. It also matches ENDPAT against every input record; when that succeeds, the range pattern is turned off again for the following record. Then it goes back to checking BEGPAT against each record. The record that turns on the range pattern and the one that turns it off both match the range pattern. If you don't want to operate on these records, you can write `if' statements in the rule's action to distinguish them from the records you are interested in. It is possible for a pattern to be turned both on and off by the same record, if the record satisfies both conditions. Then the action is executed for just that record. For example, suppose you have text between two identical markers (say the `%' symbol) that you wish to ignore. You might try to combine a range pattern that describes the delimited text with the `next' statement (not discussed yet, *note The `next' Statement: Next Statement.), which causes `awk' to skip any further processing of the current record and start over again with the next input record. Such a program would look like this: /^%$/,/^%$/ { next } { print } This program fails because the range pattern is both turned on and turned off by the first line with just a `%' on it. To accomplish this task, you must write the program this way, using a flag: /^%$/ { skip = ! skip; next } skip == 1 { next } # skip lines with `skip' set Note that in a range pattern, the `,' has the lowest precedence (is evaluated last) of all the operators. Thus, for example, the following program attempts to combine a range pattern with another, simpler test. echo Yes | awk '/1/,/2/ || /Yes/' The author of this program intended it to mean `(/1/,/2/) || /Yes/'. However, `awk' interprets this as `/1/, (/2/ || /Yes/)'. This cannot be changed or worked around; range patterns do not combine with other patterns.  File: gawk.info, Node: BEGIN/END, Next: Empty, Prev: Ranges, Up: Pattern Overview The `BEGIN' and `END' Special Patterns -------------------------------------- `BEGIN' and `END' are special patterns. They are not used to match input records. Rather, they supply start-up or clean-up actions for your `awk' script. * Menu: * Using BEGIN/END:: How and why to use BEGIN/END rules. * I/O And BEGIN/END:: I/O issues in BEGIN/END rules.  File: gawk.info, Node: Using BEGIN/END, Next: I/O And BEGIN/END, Prev: BEGIN/END, Up: BEGIN/END Startup and Cleanup Actions ........................... A `BEGIN' rule is executed, once, before the first input record has been read. An `END' rule is executed, once, after all the input has been read. For example: $ awk ' > BEGIN { print "Analysis of \"foo\"" } > /foo/ { ++n } > END { print "\"foo\" appears " n " times." }' BBS-list -| Analysis of "foo" -| "foo" appears 4 times. This program finds the number of records in the input file `BBS-list' that contain the string `foo'. The `BEGIN' rule prints a title for the report. There is no need to use the `BEGIN' rule to initialize the counter `n' to zero, as `awk' does this automatically (*note Variables::.). The second rule increments the variable `n' every time a record containing the pattern `foo' is read. The `END' rule prints the value of `n' at the end of the run. The special patterns `BEGIN' and `END' cannot be used in ranges or with boolean operators (indeed, they cannot be used with any operators). An `awk' program may have multiple `BEGIN' and/or `END' rules. They are executed in the order they appear, all the `BEGIN' rules at start-up and all the `END' rules at termination. `BEGIN' and `END' rules may be intermixed with other rules. This feature was added in the 1987 version of `awk', and is included in the POSIX standard. The original (1978) version of `awk' required you to put the `BEGIN' rule at the beginning of the program, and the `END' rule at the end, and only allowed one of each. This is no longer required, but it is a good idea in terms of program organization and readability. Multiple `BEGIN' and `END' rules are useful for writing library functions, since each library file can have its own `BEGIN' and/or `END' rule to do its own initialization and/or cleanup. Note that the order in which library functions are named on the command line controls the order in which their `BEGIN' and `END' rules are executed. Therefore you have to be careful to write such rules in library files so that the order in which they are executed doesn't matter. *Note Command Line Options: Options, for more information on using library functions. *Note A Library of `awk' Functions: Library Functions, for a number of useful library functions. If an `awk' program only has a `BEGIN' rule, and no other rules, then the program exits after the `BEGIN' rule has been run. (The original version of `awk' used to keep reading and ignoring input until end of file was seen.) However, if an `END' rule exists, then the input will be read, even if there are no other rules in the program. This is necessary in case the `END' rule checks the `FNR' and `NR' variables (d.c.). `BEGIN' and `END' rules must have actions; there is no default action for these rules since there is no current record when they run.  File: gawk.info, Node: I/O And BEGIN/END, Prev: Using BEGIN/END, Up: BEGIN/END Input/Output from `BEGIN' and `END' Rules ......................................... There are several (sometimes subtle) issues involved when doing I/O from a `BEGIN' or `END' rule. The first has to do with the value of `$0' in a `BEGIN' rule. Since `BEGIN' rules are executed before any input is read, there simply is no input record, and therefore no fields, when executing `BEGIN' rules. References to `$0' and the fields yield a null string or zero, depending upon the context. One way to give `$0' a real value is to execute a `getline' command without a variable (*note Explicit Input with `getline': Getline.). Another way is to simply assign a value to it. The second point is similar to the first, but from the other direction. Inside an `END' rule, what is the value of `$0' and `NF'? Traditionally, due largely to implementation issues, `$0' and `NF' were *undefined* inside an `END' rule. The POSIX standard specified that `NF' was available in an `END' rule, containing the number of fields from the last input record. Due most probably to an oversight, the standard does not say that `$0' is also preserved, although logically one would think that it should be. In fact, `gawk' does preserve the value of `$0' for use in `END' rules. Be aware, however, that Unix `awk', and possibly other implementations, do not. The third point follows from the first two. What is the meaning of `print' inside a `BEGIN' or `END' rule? The meaning is the same as always, `print $0'. If `$0' is the null string, then this prints an empty line. Many long time `awk' programmers use `print' in `BEGIN' and `END' rules, to mean `print ""', relying on `$0' being null. While you might generally get away with this in `BEGIN' rules, in `gawk' at least, it is a very bad idea in `END' rules. It is also poor style, since if you want an empty line in the output, you should say so explicitly in your program.  File: gawk.info, Node: Empty, Prev: BEGIN/END, Up: Pattern Overview The Empty Pattern ----------------- An empty (i.e. non-existent) pattern is considered to match *every* input record. For example, the program: awk '{ print $1 }' BBS-list prints the first field of every record.  File: gawk.info, Node: Action Overview, Prev: Pattern Overview, Up: Patterns and Actions Overview of Actions =================== An `awk' program or script consists of a series of rules and function definitions, interspersed. (Functions are described later. *Note User-defined Functions: User-defined.) A rule contains a pattern and an action, either of which (but not both) may be omitted. The purpose of the "action" is to tell `awk' what to do once a match for the pattern is found. Thus, in outline, an `awk' program generally looks like this: [PATTERN] [{ ACTION }] [PATTERN] [{ ACTION }] ... function NAME(ARGS) { ... } ... An action consists of one or more `awk' "statements", enclosed in curly braces (`{' and `}'). Each statement specifies one thing to be done. The statements are separated by newlines or semicolons. The curly braces around an action must be used even if the action contains only one statement, or even if it contains no statements at all. However, if you omit the action entirely, omit the curly braces as well. An omitted action is equivalent to `{ print $0 }'. /foo/ { } # match foo, do nothing - empty action /foo/ # match foo, print the record - omitted action Here are the kinds of statements supported in `awk': * Expressions, which can call functions or assign values to variables (*note Expressions::.). Executing this kind of statement simply computes the value of the expression. This is useful when the expression has side effects (*note Assignment Expressions: Assignment Ops.). * Control statements, which specify the control flow of `awk' programs. The `awk' language gives you C-like constructs (`if', `for', `while', and `do') as well as a few special ones (*note Control Statements in Actions: Statements.). * Compound statements, which consist of one or more statements enclosed in curly braces. A compound statement is used in order to put several statements together in the body of an `if', `while', `do' or `for' statement. * Input statements, using the `getline' command (*note Explicit Input with `getline': Getline.), the `next' statement (*note The `next' Statement: Next Statement.), and the `nextfile' statement (*note The `nextfile' Statement: Nextfile Statement.). * Output statements, `print' and `printf'. *Note Printing Output: Printing. * Deletion statements, for deleting array elements. *Note The `delete' Statement: Delete.  File: gawk.info, Node: Statements, Next: Built-in Variables, Prev: Patterns and Actions, Up: Top Control Statements in Actions ***************************** "Control statements" such as `if', `while', and so on control the flow of execution in `awk' programs. Most of the control statements in `awk' are patterned on similar statements in C. All the control statements start with special keywords such as `if' and `while', to distinguish them from simple expressions. Many control statements contain other statements; for example, the `if' statement contains another statement which may or may not be executed. The contained statement is called the "body". If you want to include more than one statement in the body, group them into a single "compound statement" with curly braces, separating them with newlines or semicolons. * Menu: * If Statement:: Conditionally execute some `awk' statements. * While Statement:: Loop until some condition is satisfied. * Do Statement:: Do specified action while looping until some condition is satisfied. * For Statement:: Another looping statement, that provides initialization and increment clauses. * Break Statement:: Immediately exit the innermost enclosing loop. * Continue Statement:: Skip to the end of the innermost enclosing loop. * Next Statement:: Stop processing the current input record. * Nextfile Statement:: Stop processing the current file. * Exit Statement:: Stop execution of `awk'.  File: gawk.info, Node: If Statement, Next: While Statement, Prev: Statements, Up: Statements The `if'-`else' Statement ========================= The `if'-`else' statement is `awk''s decision-making statement. It looks like this: if (CONDITION) THEN-BODY [else ELSE-BODY] The CONDITION is an expression that controls what the rest of the statement will do. If CONDITION is true, THEN-BODY is executed; otherwise, ELSE-BODY is executed. The `else' part of the statement is optional. The condition is considered false if its value is zero or the null string, and true otherwise. Here is an example: if (x % 2 == 0) print "x is even" else print "x is odd" In this example, if the expression `x % 2 == 0' is true (that is, the value of `x' is evenly divisible by two), then the first `print' statement is executed, otherwise the second `print' statement is executed. If the `else' appears on the same line as THEN-BODY, and THEN-BODY is not a compound statement (i.e. not surrounded by curly braces), then a semicolon must separate THEN-BODY from `else'. To illustrate this, let's rewrite the previous example: if (x % 2 == 0) print "x is even"; else print "x is odd" If you forget the `;', `awk' won't be able to interpret the statement, and you will get a syntax error. We would not actually write this example this way, because a human reader might fail to see the `else' if it were not the first thing on its line.  File: gawk.info, Node: While Statement, Next: Do Statement, Prev: If Statement, Up: Statements The `while' Statement ===================== In programming, a "loop" means a part of a program that can be executed two or more times in succession. The `while' statement is the simplest looping statement in `awk'. It repeatedly executes a statement as long as a condition is true. It looks like this: while (CONDITION) BODY Here BODY is a statement that we call the "body" of the loop, and CONDITION is an expression that controls how long the loop keeps running. The first thing the `while' statement does is test CONDITION. If CONDITION is true, it executes the statement BODY. (The CONDITION is true when the value is not zero and not a null string.) After BODY has been executed, CONDITION is tested again, and if it is still true, BODY is executed again. This process repeats until CONDITION is no longer true. If CONDITION is initially false, the body of the loop is never executed, and `awk' continues with the statement following the loop. This example prints the first three fields of each record, one per line. awk '{ i = 1 while (i <= 3) { print $i i++ } }' inventory-shipped Here the body of the loop is a compound statement enclosed in braces, containing two statements. The loop works like this: first, the value of `i' is set to one. Then, the `while' tests whether `i' is less than or equal to three. This is true when `i' equals one, so the `i'-th field is printed. Then the `i++' increments the value of `i' and the loop repeats. The loop terminates when `i' reaches four. As you can see, a newline is not required between the condition and the body; but using one makes the program clearer unless the body is a compound statement or is very simple. The newline after the open-brace that begins the compound statement is not required either, but the program would be harder to read without it.  File: gawk.info, Node: Do Statement, Next: For Statement, Prev: While Statement, Up: Statements The `do'-`while' Statement ========================== The `do' loop is a variation of the `while' looping statement. The `do' loop executes the BODY once, and then repeats BODY as long as CONDITION is true. It looks like this: do BODY while (CONDITION) Even if CONDITION is false at the start, BODY is executed at least once (and only once, unless executing BODY makes CONDITION true). Contrast this with the corresponding `while' statement: while (CONDITION) BODY This statement does not execute BODY even once if CONDITION is false to begin with. Here is an example of a `do' statement: awk '{ i = 1 do { print $0 i++ } while (i <= 10) }' This program prints each input record ten times. It isn't a very realistic example, since in this case an ordinary `while' would do just as well. But this reflects actual experience; there is only occasionally a real use for a `do' statement.  File: gawk.info, Node: For Statement, Next: Break Statement, Prev: Do Statement, Up: Statements The `for' Statement =================== The `for' statement makes it more convenient to count iterations of a loop. The general form of the `for' statement looks like this: for (INITIALIZATION; CONDITION; INCREMENT) BODY The INITIALIZATION, CONDITION and INCREMENT parts are arbitrary `awk' expressions, and BODY stands for any `awk' statement. The `for' statement starts by executing INITIALIZATION. Then, as long as CONDITION is true, it repeatedly executes BODY and then INCREMENT. Typically INITIALIZATION sets a variable to either zero or one, INCREMENT adds one to it, and CONDITION compares it against the desired number of iterations. Here is an example of a `for' statement: awk '{ for (i = 1; i <= 3; i++) print $i }' inventory-shipped This prints the first three fields of each input record, one field per line. You cannot set more than one variable in the INITIALIZATION part unless you use a multiple assignment statement such as `x = y = 0', which is possible only if all the initial values are equal. (But you can initialize additional variables by writing their assignments as separate statements preceding the `for' loop.) The same is true of the INCREMENT part; to increment additional variables, you must write separate statements at the end of the loop. The C compound expression, using C's comma operator, would be useful in this context, but it is not supported in `awk'. Most often, INCREMENT is an increment expression, as in the example above. But this is not required; it can be any expression whatever. For example, this statement prints all the powers of two between one and 100: for (i = 1; i <= 100; i *= 2) print i Any of the three expressions in the parentheses following the `for' may be omitted if there is nothing to be done there. Thus, `for (; x > 0;)' is equivalent to `while (x > 0)'. If the CONDITION is omitted, it is treated as TRUE, effectively yielding an "infinite loop" (i.e. a loop that will never terminate). In most cases, a `for' loop is an abbreviation for a `while' loop, as shown here: INITIALIZATION while (CONDITION) { BODY INCREMENT } The only exception is when the `continue' statement (*note The `continue' Statement: Continue Statement.) is used inside the loop; changing a `for' statement to a `while' statement in this way can change the effect of the `continue' statement inside the loop. There is an alternate version of the `for' loop, for iterating over all the indices of an array: for (i in array) DO SOMETHING WITH array[i] *Note Scanning All Elements of an Array: Scanning an Array, for more information on this version of the `for' loop. The `awk' language has a `for' statement in addition to a `while' statement because often a `for' loop is both less work to type and more natural to think of. Counting the number of iterations is very common in loops. It can be easier to think of this counting as part of looping rather than as something to do inside the loop. The next section has more complicated examples of `for' loops.  File: gawk.info, Node: Break Statement, Next: Continue Statement, Prev: For Statement, Up: Statements The `break' Statement ===================== The `break' statement jumps out of the innermost `for', `while', or `do' loop that encloses it. The following example finds the smallest divisor of any integer, and also identifies prime numbers: awk '# find smallest divisor of num { num = $1 for (div = 2; div*div <= num; div++) if (num % div == 0) break if (num % div == 0) printf "Smallest divisor of %d is %d\n", num, div else printf "%d is prime\n", num }' When the remainder is zero in the first `if' statement, `awk' immediately "breaks out" of the containing `for' loop. This means that `awk' proceeds immediately to the statement following the loop and continues processing. (This is very different from the `exit' statement which stops the entire `awk' program. *Note The `exit' Statement: Exit Statement.) Here is another program equivalent to the previous one. It illustrates how the CONDITION of a `for' or `while' could just as well be replaced with a `break' inside an `if': awk '# find smallest divisor of num { num = $1 for (div = 2; ; div++) { if (num % div == 0) { printf "Smallest divisor of %d is %d\n", num, div break } if (div*div > num) { printf "%d is prime\n", num break } } }' As described above, the `break' statement has no meaning when used outside the body of a loop. However, although it was never documented, historical implementations of `awk' have treated the `break' statement outside of a loop as if it were a `next' statement (*note The `next' Statement: Next Statement.). Recent versions of Unix `awk' no longer allow this usage. `gawk' will support this use of `break' only if `--traditional' has been specified on the command line (*note Command Line Options: Options.). Otherwise, it will be treated as an error, since the POSIX standard specifies that `break' should only be used inside the body of a loop (d.c.).  File: gawk.info, Node: Continue Statement, Next: Next Statement, Prev: Break Statement, Up: Statements The `continue' Statement ======================== The `continue' statement, like `break', is used only inside `for', `while', and `do' loops. It skips over the rest of the loop body, causing the next cycle around the loop to begin immediately. Contrast this with `break', which jumps out of the loop altogether. The `continue' statement in a `for' loop directs `awk' to skip the rest of the body of the loop, and resume execution with the increment-expression of the `for' statement. The following program illustrates this fact: awk 'BEGIN { for (x = 0; x <= 20; x++) { if (x == 5) continue printf "%d ", x } print "" }' This program prints all the numbers from zero to 20, except for five, for which the `printf' is skipped. Since the increment `x++' is not skipped, `x' does not remain stuck at five. Contrast the `for' loop above with this `while' loop: awk 'BEGIN { x = 0 while (x <= 20) { if (x == 5) continue printf "%d ", x x++ } print "" }' This program loops forever once `x' gets to five. As described above, the `continue' statement has no meaning when used outside the body of a loop. However, although it was never documented, historical implementations of `awk' have treated the `continue' statement outside of a loop as if it were a `next' statement (*note The `next' Statement: Next Statement.). Recent versions of Unix `awk' no longer allow this usage. `gawk' will support this use of `continue' only if `--traditional' has been specified on the command line (*note Command Line Options: Options.). Otherwise, it will be treated as an error, since the POSIX standard specifies that `continue' should only be used inside the body of a loop (d.c.).  File: gawk.info, Node: Next Statement, Next: Nextfile Statement, Prev: Continue Statement, Up: Statements The `next' Statement ==================== The `next' statement forces `awk' to immediately stop processing the current record and go on to the next record. This means that no further rules are executed for the current record. The rest of the current rule's action is not executed either. Contrast this with the effect of the `getline' function (*note Explicit Input with `getline': Getline.). That too causes `awk' to read the next record immediately, but it does not alter the flow of control in any way. So the rest of the current action executes with a new input record. At the highest level, `awk' program execution is a loop that reads an input record and then tests each rule's pattern against it. If you think of this loop as a `for' statement whose body contains the rules, then the `next' statement is analogous to a `continue' statement: it skips to the end of the body of this implicit loop, and executes the increment (which reads another record). For example, if your `awk' program works only on records with four fields, and you don't want it to fail when given bad input, you might use this rule near the beginning of the program: NF != 4 { err = sprintf("%s:%d: skipped: NF != 4\n", FILENAME, FNR) print err > "/dev/stderr" next } so that the following rules will not see the bad record. The error message is redirected to the standard error output stream, as error messages should be. *Note Special File Names in `gawk': Special Files. According to the POSIX standard, the behavior is undefined if the `next' statement is used in a `BEGIN' or `END' rule. `gawk' will treat it as a syntax error. Although POSIX permits it, some other `awk' implementations don't allow the `next' statement inside function bodies (*note User-defined Functions: User-defined.). Just as any other `next' statement, a `next' inside a function body reads the next record and starts processing it with the first rule in the program. If the `next' statement causes the end of the input to be reached, then the code in any `END' rules will be executed. *Note The `BEGIN' and `END' Special Patterns: BEGIN/END. *Caution:* Some `awk' implementations generate a run-time error if you use the `next' statement inside a user-defined function (*note User-defined Functions: User-defined.). `gawk' does not have this problem.  File: gawk.info, Node: Nextfile Statement, Next: Exit Statement, Prev: Next Statement, Up: Statements The `nextfile' Statement ======================== `gawk' provides the `nextfile' statement, which is similar to the `next' statement. However, instead of abandoning processing of the current record, the `nextfile' statement instructs `gawk' to stop processing the current data file. Upon execution of the `nextfile' statement, `FILENAME' is updated to the name of the next data file listed on the command line, `FNR' is reset to one, `ARGIND' is incremented, and processing starts over with the first rule in the progam. *Note Built-in Variables::. If the `nextfile' statement causes the end of the input to be reached, then the code in any `END' rules will be executed. *Note The `BEGIN' and `END' Special Patterns: BEGIN/END. The `nextfile' statement is a `gawk' extension; it is not (currently) available in any other `awk' implementation. *Note Implementing `nextfile' as a Function: Nextfile Function, for a user-defined function you can use to simulate the `nextfile' statement. The `nextfile' statement would be useful if you have many data files to process, and you expect that you would not want to process every record in every file. Normally, in order to move on to the next data file, you would have to continue scanning the unwanted records. The `nextfile' statement accomplishes this much more efficiently. *Caution:* Versions of `gawk' prior to 3.0 used two words (`next file') for the `nextfile' statement. This was changed in 3.0 to one word, since the treatment of `file' was inconsistent. When it appeared after `next', it was a keyword. Otherwise, it was a regular identifier. The old usage is still accepted. However, `gawk' will generate a warning message, and support for `next file' will eventually be discontinued in a future version of `gawk'.  File: gawk.info, Node: Exit Statement, Prev: Nextfile Statement, Up: Statements The `exit' Statement ==================== The `exit' statement causes `awk' to immediately stop executing the current rule and to stop processing input; any remaining input is ignored. It looks like this: exit [RETURN CODE] If an `exit' statement is executed from a `BEGIN' rule the program stops processing everything immediately. No input records are read. However, if an `END' rule is present, it is executed (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). If `exit' is used as part of an `END' rule, it causes the program to stop immediately. An `exit' statement that is not part of a `BEGIN' or `END' rule stops the execution of any further automatic rules for the current record, skips reading any remaining input records, and executes the `END' rule if there is one. If you do not want the `END' rule to do its job in this case, you can set a variable to non-zero before the `exit' statement, and check that variable in the `END' rule. *Note Assertions: Assert Function, for an example that does this. If an argument is supplied to `exit', its value is used as the exit status code for the `awk' process. If no argument is supplied, `exit' returns status zero (success). In the case where an argument is supplied to a first `exit' statement, and then `exit' is called a second time with no argument, the previously supplied exit value is used (d.c.). For example, let's say you've discovered an error condition you really don't know how to handle. Conventionally, programs report this by exiting with a non-zero status. Your `awk' program can do this using an `exit' statement with a non-zero argument. Here is an example: BEGIN { if (("date" | getline date_now) < 0) { print "Can't get system date" > "/dev/stderr" exit 1 } print "current date is", date_now close("date") }  File: gawk.info, Node: Built-in Variables, Next: Arrays, Prev: Statements, Up: Top Built-in Variables ****************** Most `awk' variables are available for you to use for your own purposes; they never change except when your program assigns values to them, and never affect anything except when your program examines them. However, a few variables in `awk' have special built-in meanings. Some of them `awk' examines automatically, so that they enable you to tell `awk' how to do certain things. Others are set automatically by `awk', so that they carry information from the internal workings of `awk' to your program. This chapter documents all the built-in variables of `gawk'. Most of them are also documented in the chapters describing their areas of activity. * Menu: * User-modified:: Built-in variables that you change to control `awk'. * Auto-set:: Built-in variables where `awk' gives you information. * ARGC and ARGV:: Ways to use `ARGC' and `ARGV'.  File: gawk.info, Node: User-modified, Next: Auto-set, Prev: Built-in Variables, Up: Built-in Variables Built-in Variables that Control `awk' ===================================== This is an alphabetical list of the variables which you can change to control how `awk' does certain things. Those variables that are specific to `gawk' are marked with an asterisk, `*'. `CONVFMT' This string controls conversion of numbers to strings (*note Conversion of Strings and Numbers: Conversion.). It works by being passed, in effect, as the first argument to the `sprintf' function (*note Built-in Functions for String Manipulation: String Functions.). Its default value is `"%.6g"'. `CONVFMT' was introduced by the POSIX standard. `FIELDWIDTHS *' This is a space separated list of columns that tells `gawk' how to split input with fixed, columnar boundaries. It is an experimental feature. Assigning to `FIELDWIDTHS' overrides the use of `FS' for field splitting. *Note Reading Fixed-width Data: Constant Size, for more information. If `gawk' is in compatibility mode (*note Command Line Options: Options.), then `FIELDWIDTHS' has no special meaning, and field splitting operations are done based exclusively on the value of `FS'. `FS' `FS' is the input field separator (*note Specifying How Fields are Separated: Field Separators.). The value is a single-character string or a multi-character regular expression that matches the separations between fields in an input record. If the value is the null string (`""'), then each character in the record becomes a separate field. The default value is `" "', a string consisting of a single space. As a special exception, this value means that any sequence of spaces, tabs, and/or newlines is a single separator.(1) It also causes spaces, tabs, and newlines at the beginning and end of a record to be ignored. You can set the value of `FS' on the command line using the `-F' option: awk -F, 'PROGRAM' INPUT-FILES If `gawk' is using `FIELDWIDTHS' for field-splitting, assigning a value to `FS' will cause `gawk' to return to the normal, `FS'-based, field splitting. An easy way to do this is to simply say `FS = FS', perhaps with an explanatory comment. `IGNORECASE *' If `IGNORECASE' is non-zero or non-null, then all string comparisons, and all regular expression matching are case-independent. Thus, regexp matching with `~' and `!~', and the `gensub', `gsub', `index', `match', `split' and `sub' functions, record termination with `RS', and field splitting with `FS' all ignore case when doing their particular regexp operations. The value of `IGNORECASE' does *not* affect array subscripting. *Note Case-sensitivity in Matching: Case-sensitivity. If `gawk' is in compatibility mode (*note Command Line Options: Options.), then `IGNORECASE' has no special meaning, and string and regexp operations are always case-sensitive. `OFMT' This string controls conversion of numbers to strings (*note Conversion of Strings and Numbers: Conversion.) for printing with the `print' statement. It works by being passed, in effect, as the first argument to the `sprintf' function (*note Built-in Functions for String Manipulation: String Functions.). Its default value is `"%.6g"'. Earlier versions of `awk' also used `OFMT' to specify the format for converting numbers to strings in general expressions; this is now done by `CONVFMT'. `OFS' This is the output field separator (*note Output Separators::.). It is output between the fields output by a `print' statement. Its default value is `" "', a string consisting of a single space. `ORS' This is the output record separator. It is output at the end of every `print' statement. Its default value is `"\n"'. (*Note Output Separators::.) `RS' This is `awk''s input record separator. Its default value is a string containing a single newline character, which means that an input record consists of a single line of text. It can also be the null string, in which case records are separated by runs of blank lines, or a regexp, in which case records are separated by matches of the regexp in the input text. (*Note How Input is Split into Records: Records.) `SUBSEP' `SUBSEP' is the subscript separator. It has the default value of `"\034"', and is used to separate the parts of the indices of a multi-dimensional array. Thus, the expression `foo["A", "B"]' really accesses `foo["A\034B"]' (*note Multi-dimensional Arrays: Multi-dimensional.). ---------- Footnotes ---------- (1) In POSIX `awk', newline does not count as whitespace.  File: gawk.info, Node: Auto-set, Next: ARGC and ARGV, Prev: User-modified, Up: Built-in Variables Built-in Variables that Convey Information ========================================== This is an alphabetical list of the variables that are set automatically by `awk' on certain occasions in order to provide information to your program. Those variables that are specific to `gawk' are marked with an asterisk, `*'. `ARGC' `ARGV' The command-line arguments available to `awk' programs are stored in an array called `ARGV'. `ARGC' is the number of command-line arguments present. *Note Other Command Line Arguments: Other Arguments. Unlike most `awk' arrays, `ARGV' is indexed from zero to `ARGC' - 1. For example: $ awk 'BEGIN { > for (i = 0; i < ARGC; i++) > print ARGV[i] > }' inventory-shipped BBS-list -| awk -| inventory-shipped -| BBS-list In this example, `ARGV[0]' contains `"awk"', `ARGV[1]' contains `"inventory-shipped"', and `ARGV[2]' contains `"BBS-list"'. The value of `ARGC' is three, one more than the index of the last element in `ARGV', since the elements are numbered from zero. The names `ARGC' and `ARGV', as well as the convention of indexing the array from zero to `ARGC' - 1, are derived from the C language's method of accessing command line arguments. *Note Using `ARGC' and `ARGV': ARGC and ARGV, for information about how `awk' uses these variables. `ARGIND *' The index in `ARGV' of the current file being processed. Every time `gawk' opens a new data file for processing, it sets `ARGIND' to the index in `ARGV' of the file name. When `gawk' is processing the input files, it is always true that `FILENAME == ARGV[ARGIND]'. This variable is useful in file processing; it allows you to tell how far along you are in the list of data files, and to distinguish between successive instances of the same filename on the command line. While you can change the value of `ARGIND' within your `awk' program, `gawk' will automatically set it to a new value when the next file is opened. This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note Command Line Options: Options.), it is not special. `ENVIRON' An associative array that contains the values of the environment. The array indices are the environment variable names; the values are the values of the particular environment variables. For example, `ENVIRON["HOME"]' might be `/home/arnold'. Changing this array does not affect the environment passed on to any programs that `awk' may spawn via redirection or the `system' function. (In a future version of `gawk', it may do so.) Some operating systems may not have environment variables. On such systems, the `ENVIRON' array is empty (except for `ENVIRON["AWKPATH"]'). `ERRNO *' If a system error occurs either doing a redirection for `getline', during a read for `getline', or during a `close' operation, then `ERRNO' will contain a string describing the error. This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note Command Line Options: Options.), it is not special. `FILENAME' This is the name of the file that `awk' is currently reading. When no data files are listed on the command line, `awk' reads from the standard input, and `FILENAME' is set to `"-"'. `FILENAME' is changed each time a new file is read (*note Reading Input Files: Reading Files.). Inside a `BEGIN' rule, the value of `FILENAME' is `""', since there are no input files being processed yet.(1) (d.c.) `FNR' `FNR' is the current record number in the current file. `FNR' is incremented each time a new record is read (*note Explicit Input with `getline': Getline.). It is reinitialized to zero each time a new input file is started. `NF' `NF' is the number of fields in the current input record. `NF' is set each time a new record is read, when a new field is created, or when `$0' changes (*note Examining Fields: Fields.). `NR' This is the number of input records `awk' has processed since the beginning of the program's execution (*note How Input is Split into Records: Records.). `NR' is set each time a new record is read. `RLENGTH' `RLENGTH' is the length of the substring matched by the `match' function (*note Built-in Functions for String Manipulation: String Functions.). `RLENGTH' is set by invoking the `match' function. Its value is the length of the matched string, or -1 if no match was found. `RSTART' `RSTART' is the start-index in characters of the substring matched by the `match' function (*note Built-in Functions for String Manipulation: String Functions.). `RSTART' is set by invoking the `match' function. Its value is the position of the string where the matched substring starts, or zero if no match was found. `RT *' `RT' is set each time a record is read. It contains the input text that matched the text denoted by `RS', the record separator. This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note Command Line Options: Options.), it is not special. A side note about `NR' and `FNR'. `awk' simply increments both of these variables each time it reads a record, instead of setting them to the absolute value of the number of records read. This means that your program can change these variables, and their new values will be incremented for each record (d.c.). For example: $ echo '1 > 2 > 3 > 4' | awk 'NR == 2 { NR = 17 } > { print NR }' -| 1 -| 17 -| 18 -| 19 Before `FNR' was added to the `awk' language (*note Major Changes between V7 and SVR3.1: V7/SVR3.1.), many `awk' programs used this feature to track the number of records in a file by resetting `NR' to zero when `FILENAME' changed. ---------- Footnotes ---------- (1) Some early implementations of Unix `awk' initialized `FILENAME' to `"-"', even if there were data files to be processed. This behavior was incorrect, and should not be relied upon in your programs.  File: gawk.info, Node: ARGC and ARGV, Prev: Auto-set, Up: Built-in Variables Using `ARGC' and `ARGV' ======================= In *Note Built-in Variables that Convey Information: Auto-set, you saw this program describing the information contained in `ARGC' and `ARGV': $ awk 'BEGIN { > for (i = 0; i < ARGC; i++) > print ARGV[i] > }' inventory-shipped BBS-list -| awk -| inventory-shipped -| BBS-list In this example, `ARGV[0]' contains `"awk"', `ARGV[1]' contains `"inventory-shipped"', and `ARGV[2]' contains `"BBS-list"'. Notice that the `awk' program is not entered in `ARGV'. The other special command line options, with their arguments, are also not entered. But variable assignments on the command line *are* treated as arguments, and do show up in the `ARGV' array. Your program can alter `ARGC' and the elements of `ARGV'. Each time `awk' reaches the end of an input file, it uses the next element of `ARGV' as the name of the next input file. By storing a different string there, your program can change which files are read. You can use `"-"' to represent the standard input. By storing additional elements and incrementing `ARGC' you can cause additional files to be read. If you decrease the value of `ARGC', that eliminates input files from the end of the list. By recording the old value of `ARGC' elsewhere, your program can treat the eliminated arguments as something other than file names. To eliminate a file from the middle of the list, store the null string (`""') into `ARGV' in place of the file's name. As a special feature, `awk' ignores file names that have been replaced with the null string. You may also use the `delete' statement to remove elements from `ARGV' (*note The `delete' Statement: Delete.). All of these actions are typically done from the `BEGIN' rule, before actual processing of the input begins. *Note Splitting a Large File Into Pieces: Split Program, and see *Note Duplicating Output Into Multiple Files: Tee Program, for an example of each way of removing elements from `ARGV'. The following fragment processes `ARGV' in order to examine, and then remove, command line options. BEGIN { for (i = 1; i < ARGC; i++) { if (ARGV[i] == "-v") verbose = 1 else if (ARGV[i] == "-d") debug = 1 else if (ARGV[i] ~ /^-?/) { e = sprintf("%s: unrecognized option -- %c", ARGV[0], substr(ARGV[i], 1, ,1)) print e > "/dev/stderr" } else break delete ARGV[i] } } To actually get the options into the `awk' program, you have to end the `awk' options with `--', and then supply your options, like so: awk -f myprog -- -v -d file1 file2 ... This is not necessary in `gawk': Unless `--posix' has been specified, `gawk' silently puts any unrecognized options into `ARGV' for the `awk' program to deal with. As soon as it sees an unknown option, `gawk' stops looking for other options it might otherwise recognize. The above example with `gawk' would be: gawk -f myprog -d -v file1 file2 ... Since `-d' is not a valid `gawk' option, the following `-v' is passed on to the `awk' program.  File: gawk.info, Node: Arrays, Next: Built-in, Prev: Built-in Variables, Up: Top Arrays in `awk' *************** An "array" is a table of values, called "elements". The elements of an array are distinguished by their indices. "Indices" may be either numbers or strings. `awk' maintains a single set of names that may be used for naming variables, arrays and functions (*note User-defined Functions: User-defined.). Thus, you cannot have a variable and an array with the same name in the same `awk' program. * Menu: * Array Intro:: Introduction to Arrays * Reference to Elements:: How to examine one element of an array. * Assigning Elements:: How to change an element of an array. * Array Example:: Basic Example of an Array * Scanning an Array:: A variation of the `for' statement. It loops through the indices of an array's existing elements. * Delete:: The `delete' statement removes an element from an array. * Numeric Array Subscripts:: How to use numbers as subscripts in `awk'. * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. * Multi-dimensional:: Emulating multi-dimensional arrays in `awk'. * Multi-scanning:: Scanning multi-dimensional arrays.  File: gawk.info, Node: Array Intro, Next: Reference to Elements, Prev: Arrays, Up: Arrays Introduction to Arrays ====================== The `awk' language provides one-dimensional "arrays" for storing groups of related strings or numbers. Every `awk' array must have a name. Array names have the same syntax as variable names; any valid variable name would also be a valid array name. But you cannot use one name in both ways (as an array and as a variable) in one `awk' program. Arrays in `awk' superficially resemble arrays in other programming languages; but there are fundamental differences. In `awk', you don't need to specify the size of an array before you start to use it. Additionally, any number or string in `awk' may be used as an array index, not just consecutive integers. In most other languages, you have to "declare" an array and specify how many elements or components it contains. In such languages, the declaration causes a contiguous block of memory to be allocated for that many elements. An index in the array usually must be a positive integer; for example, the index zero specifies the first element in the array, which is actually stored at the beginning of the block of memory. Index one specifies the second element, which is stored in memory right after the first element, and so on. It is impossible to add more elements to the array, because it has room for only as many elements as you declared. (Some languages allow arbitrary starting and ending indices, e.g., `15 .. 27', but the size of the array is still fixed when the array is declared.) A contiguous array of four elements might look like this, conceptually, if the element values are eight, `"foo"', `""' and 30: +---------+---------+--------+---------+ | 8 | "foo" | "" | 30 | value +---------+---------+--------+---------+ 0 1 2 3 index Only the values are stored; the indices are implicit from the order of the values. Eight is the value at index zero, because eight appears in the position with zero elements before it. Arrays in `awk' are different: they are "associative". This means that each array is a collection of pairs: an index, and its corresponding array element value: Element 4 Value 30 Element 2 Value "foo" Element 1 Value 8 Element 3 Value "" We have shown the pairs in jumbled order because their order is irrelevant. One advantage of associative arrays is that new pairs can be added at any time. For example, suppose we add to the above array a tenth element whose value is `"number ten"'. The result is this: Element 10 Value "number ten" Element 4 Value 30 Element 2 Value "foo" Element 1 Value 8 Element 3 Value "" Now the array is "sparse", which just means some indices are missing: it has elements 1-4 and 10, but doesn't have elements 5, 6, 7, 8, or 9. Another consequence of associative arrays is that the indices don't have to be positive integers. Any number, or even a string, can be an index. For example, here is an array which translates words from English into French: Element "dog" Value "chien" Element "cat" Value "chat" Element "one" Value "un" Element 1 Value "un" Here we decided to translate the number one in both spelled-out and numeric form--thus illustrating that a single array can have both numbers and strings as indices. (In fact, array subscripts are always strings; this is discussed in more detail in *Note Using Numbers to Subscript Arrays: Numeric Array Subscripts.) The value of `IGNORECASE' has no effect upon array subscripting. You must use the exact same string value to retrieve an array element as you used to store it. When `awk' creates an array for you, e.g., with the `split' built-in function, that array's indices are consecutive integers starting at one. (*Note Built-in Functions for String Manipulation: String Functions.)  File: gawk.info, Node: Reference to Elements, Next: Assigning Elements, Prev: Array Intro, Up: Arrays Referring to an Array Element ============================= The principal way of using an array is to refer to one of its elements. An array reference is an expression which looks like this: ARRAY[INDEX] Here, ARRAY is the name of an array. The expression INDEX is the index of the element of the array that you want. The value of the array reference is the current value of that array element. For example, `foo[4.3]' is an expression for the element of array `foo' at index `4.3'. If you refer to an array element that has no recorded value, the value of the reference is `""', the null string. This includes elements to which you have not assigned any value, and elements that have been deleted (*note The `delete' Statement: Delete.). Such a reference automatically creates that array element, with the null string as its value. (In some cases, this is unfortunate, because it might waste memory inside `awk'.) You can find out if an element exists in an array at a certain index with the expression: INDEX in ARRAY This expression tests whether or not the particular index exists, without the side effect of creating that element if it is not present. The expression has the value one (true) if `ARRAY[INDEX]' exists, and zero (false) if it does not exist. For example, to test whether the array `frequencies' contains the index `2', you could write this statement: if (2 in frequencies) print "Subscript 2 is present." Note that this is *not* a test of whether or not the array `frequencies' contains an element whose *value* is two. (There is no way to do that except to scan all the elements.) Also, this *does not* create `frequencies[2]', while the following (incorrect) alternative would do so: if (frequencies[2] != "") print "Subscript 2 is present."  File: gawk.info, Node: Assigning Elements, Next: Array Example, Prev: Reference to Elements, Up: Arrays Assigning Array Elements ======================== Array elements are lvalues: they can be assigned values just like `awk' variables: ARRAY[SUBSCRIPT] = VALUE Here ARRAY is the name of your array. The expression SUBSCRIPT is the index of the element of the array that you want to assign a value. The expression VALUE is the value you are assigning to that element of the array.  File: gawk.info, Node: Array Example, Next: Scanning an Array, Prev: Assigning Elements, Up: Arrays Basic Array Example =================== The following program takes a list of lines, each beginning with a line number, and prints them out in order of line number. The line numbers are not in order, however, when they are first read: they are scrambled. This program sorts the lines by making an array using the line numbers as subscripts. It then prints out the lines in sorted order of their numbers. It is a very simple program, and gets confused if it encounters repeated numbers, gaps, or lines that don't begin with a number. { if ($1 > max) max = $1 arr[$1] = $0 } END { for (x = 1; x <= max; x++) print arr[x] } The first rule keeps track of the largest line number seen so far; it also stores each line into the array `arr', at an index that is the line's number. The second rule runs after all the input has been read, to print out all the lines. When this program is run with the following input: 5 I am the Five man 2 Who are you? The new number two! 4 . . . And four on the floor 1 Who is number one? 3 I three you. its output is this: 1 Who is number one? 2 Who are you? The new number two! 3 I three you. 4 . . . And four on the floor 5 I am the Five man If a line number is repeated, the last line with a given number overrides the others. Gaps in the line numbers can be handled with an easy improvement to the program's `END' rule: END { for (x = 1; x <= max; x++) if (x in arr) print arr[x] }  File: gawk.info, Node: Scanning an Array, Next: Delete, Prev: Array Example, Up: Arrays Scanning All Elements of an Array ================================= In programs that use arrays, you often need a loop that executes once for each element of an array. In other languages, where arrays are contiguous and indices are limited to positive integers, this is easy: you can find all the valid indices by counting from the lowest index up to the highest. This technique won't do the job in `awk', since any number or string can be an array index. So `awk' has a special kind of `for' statement for scanning an array: for (VAR in ARRAY) BODY This loop executes BODY once for each index in ARRAY that your program has previously used, with the variable VAR set to that index. Here is a program that uses this form of the `for' statement. The first rule scans the input records and notes which words appear (at least once) in the input, by storing a one into the array `used' with the word as index. The second rule scans the elements of `used' to find all the distinct words that appear in the input. It prints each word that is more than 10 characters long, and also prints the number of such words. *Note Built-in Functions for String Manipulation: String Functions, for more information on the built-in function `length'. # Record a 1 for each word that is used at least once. { for (i = 1; i <= NF; i++) used[$i] = 1 } # Find number of distinct words more than 10 characters long. END { for (x in used) if (length(x) > 10) { ++num_long_words print x } print num_long_words, "words longer than 10 characters" } *Note Generating Word Usage Counts: Word Sorting, for a more detailed example of this type. The order in which elements of the array are accessed by this statement is determined by the internal arrangement of the array elements within `awk' and cannot be controlled or changed. This can lead to problems if new elements are added to ARRAY by statements in the loop body; you cannot predict whether or not the `for' loop will reach them. Similarly, changing VAR inside the loop may produce strange results. It is best to avoid such things.  File: gawk.info, Node: Delete, Next: Numeric Array Subscripts, Prev: Scanning an Array, Up: Arrays The `delete' Statement ====================== You can remove an individual element of an array using the `delete' statement: delete ARRAY[INDEX] Once you have deleted an array element, you can no longer obtain any value the element once had. It is as if you had never referred to it and had never given it any value. Here is an example of deleting elements in an array: for (i in frequencies) delete frequencies[i] This example removes all the elements from the array `frequencies'. If you delete an element, a subsequent `for' statement to scan the array will not report that element, and the `in' operator to check for the presence of that element will return zero (i.e. false): delete foo[4] if (4 in foo) print "This will never be printed" It is important to note that deleting an element is *not* the same as assigning it a null value (the empty string, `""'). foo[4] = "" if (4 in foo) print "This is printed, even though foo[4] is empty" It is not an error to delete an element that does not exist. You can delete all the elements of an array with a single statement, by leaving off the subscript in the `delete' statement. delete ARRAY This ability is a `gawk' extension; it is not available in compatibility mode (*note Command Line Options: Options.). Using this version of the `delete' statement is about three times more efficient than the equivalent loop that deletes each element one at a time. The following statement provides a portable, but non-obvious way to clear out an array. # thanks to Michael Brennan for pointing this out split("", array) The `split' function (*note Built-in Functions for String Manipulation: String Functions.) clears out the target array first. This call asks it to split apart the null string. Since there is no data to split out, the function simply clears the array and then returns.  File: gawk.info, Node: Numeric Array Subscripts, Next: Uninitialized Subscripts, Prev: Delete, Up: Arrays Using Numbers to Subscript Arrays ================================= An important aspect of arrays to remember is that *array subscripts are always strings*. If you use a numeric value as a subscript, it will be converted to a string value before it is used for subscripting (*note Conversion of Strings and Numbers: Conversion.). This means that the value of the built-in variable `CONVFMT' can potentially affect how your program accesses elements of an array. For example: xyz = 12.153 data[xyz] = 1 CONVFMT = "%2.2f" if (xyz in data) printf "%s is in data\n", xyz else printf "%s is not in data\n", xyz This prints `12.15 is not in data'. The first statement gives `xyz' a numeric value. Assigning to `data[xyz]' subscripts `data' with the string value `"12.153"' (using the default conversion value of `CONVFMT', `"%.6g"'), and assigns one to `data["12.153"]'. The program then changes the value of `CONVFMT'. The test `(xyz in data)' generates a new string value from `xyz', this time `"12.15"', since the value of `CONVFMT' only allows two significant digits. This test fails, since `"12.15"' is a different string from `"12.153"'. According to the rules for conversions (*note Conversion of Strings and Numbers: Conversion.), integer values are always converted to strings as integers, no matter what the value of `CONVFMT' may happen to be. So the usual case of: for (i = 1; i <= maxsub; i++) do something with array[i] will work, no matter what the value of `CONVFMT'. Like many things in `awk', the majority of the time things work as you would expect them to work. But it is useful to have a precise knowledge of the actual rules, since sometimes they can have a subtle effect on your programs.  File: gawk.info, Node: Uninitialized Subscripts, Next: Multi-dimensional, Prev: Numeric Array Subscripts, Up: Arrays Using Uninitialized Variables as Subscripts =========================================== Suppose you want to print your input data in reverse order. A reasonable attempt at a program to do so (with some test data) might look like this: $ echo 'line 1 > line 2 > line 3' | awk '{ l[lines] = $0; ++lines } > END { > for (i = lines-1; i >= 0; --i) > print l[i] > }' -| line 3 -| line 2 Unfortunately, the very first line of input data did not come out in the output! At first glance, this program should have worked. The variable `lines' is uninitialized, and uninitialized variables have the numeric value zero. So, the value of `l[0]' should have been printed. The issue here is that subscripts for `awk' arrays are *always* strings. And uninitialized variables, when used as strings, have the value `""', not zero. Thus, `line 1' ended up stored in `l[""]'. The following version of the program works correctly: { l[lines++] = $0 } END { for (i = lines - 1; i >= 0; --i) print l[i] } Here, the `++' forces `lines' to be numeric, thus making the "old value" numeric zero, which is then converted to `"0"' as the array subscript. As we have just seen, even though it is somewhat unusual, the null string (`""') is a valid array subscript (d.c.). If `--lint' is provided on the command line (*note Command Line Options: Options.), `gawk' will warn about the use of the null string as a subscript.  File: gawk.info, Node: Multi-dimensional, Next: Multi-scanning, Prev: Uninitialized Subscripts, Up: Arrays Multi-dimensional Arrays ======================== A multi-dimensional array is an array in which an element is identified by a sequence of indices, instead of a single index. For example, a two-dimensional array requires two indices. The usual way (in most languages, including `awk') to refer to an element of a two-dimensional array named `grid' is with `grid[X,Y]'. Multi-dimensional arrays are supported in `awk' through concatenation of indices into one string. What happens is that `awk' converts the indices into strings (*note Conversion of Strings and Numbers: Conversion.) and concatenates them together, with a separator between them. This creates a single string that describes the values of the separate indices. The combined string is used as a single index into an ordinary, one-dimensional array. The separator used is the value of the built-in variable `SUBSEP'. For example, suppose we evaluate the expression `foo[5,12] = "value"' when the value of `SUBSEP' is `"@@"'. The numbers five and 12 are converted to strings and concatenated with an `@@' between them, yielding `"5@@12"'; thus, the array element `foo["5@@12"]' is set to `"value"'. Once the element's value is stored, `awk' has no record of whether it was stored with a single index or a sequence of indices. The two expressions `foo[5,12]' and `foo[5 SUBSEP 12]' are always equivalent. The default value of `SUBSEP' is the string `"\034"', which contains a non-printing character that is unlikely to appear in an `awk' program or in most input data. The usefulness of choosing an unlikely character comes from the fact that index values that contain a string matching `SUBSEP' lead to combined strings that are ambiguous. Suppose that `SUBSEP' were `"@@"'; then `foo["a@@b", "c"]' and `foo["a", "b@@c"]' would be indistinguishable because both would actually be stored as `foo["a@@b@@c"]'. You can test whether a particular index-sequence exists in a "multi-dimensional" array with the same operator `in' used for single dimensional arrays. Instead of a single index as the left-hand operand, write the whole sequence of indices, separated by commas, in parentheses: (SUBSCRIPT1, SUBSCRIPT2, ...) in ARRAY The following example treats its input as a two-dimensional array of fields; it rotates this array 90 degrees clockwise and prints the result. It assumes that all lines have the same number of elements. awk '{ if (max_nf < NF) max_nf = NF max_nr = NR for (x = 1; x <= NF; x++) vector[x, NR] = $x } END { for (x = 1; x <= max_nf; x++) { for (y = max_nr; y >= 1; --y) printf("%s ", vector[x, y]) printf("\n") } }' When given the input: 1 2 3 4 5 6 2 3 4 5 6 1 3 4 5 6 1 2 4 5 6 1 2 3 it produces: 4 3 2 1 5 4 3 2 6 5 4 3 1 6 5 4 2 1 6 5 3 2 1 6  File: gawk.info, Node: Multi-scanning, Prev: Multi-dimensional, Up: Arrays Scanning Multi-dimensional Arrays ================================= There is no special `for' statement for scanning a "multi-dimensional" array; there cannot be one, because in truth there are no multi-dimensional arrays or elements; there is only a multi-dimensional *way of accessing* an array. However, if your program has an array that is always accessed as multi-dimensional, you can get the effect of scanning it by combining the scanning `for' statement (*note Scanning All Elements of an Array: Scanning an Array.) with the `split' built-in function (*note Built-in Functions for String Manipulation: String Functions.). It works like this: for (combined in array) { split(combined, separate, SUBSEP) ... } This sets `combined' to each concatenated, combined index in the array, and splits it into the individual indices by breaking it apart where the value of `SUBSEP' appears. The split-out indices become the elements of the array `separate'. Thus, suppose you have previously stored a value in `array[1, "foo"]'; then an element with index `"1\034foo"' exists in `array'. (Recall that the default value of `SUBSEP' is the character with code 034.) Sooner or later the `for' statement will find that index and do an iteration with `combined' set to `"1\034foo"'. Then the `split' function is called as follows: split("1\034foo", separate, "\034") The result of this is to set `separate[1]' to `"1"' and `separate[2]' to `"foo"'. Presto, the original sequence of separate indices has been recovered.  File: gawk.info, Node: Built-in, Next: User-defined, Prev: Arrays, Up: Top Built-in Functions ****************** "Built-in" functions are functions that are always available for your `awk' program to call. This chapter defines all the built-in functions in `awk'; some of them are mentioned in other sections, but they are summarized here for your convenience. (You can also define new functions yourself. *Note User-defined Functions: User-defined.) * Menu: * Calling Built-in:: How to call built-in functions. * Numeric Functions:: Functions that work with numbers, including `int', `sin' and `rand'. * String Functions:: Functions for string manipulation, such as `split', `match', and `sprintf'. * I/O Functions:: Functions for files and shell commands. * Time Functions:: Functions for dealing with time stamps.  File: gawk.info, Node: Calling Built-in, Next: Numeric Functions, Prev: Built-in, Up: Built-in Calling Built-in Functions ========================== To call a built-in function, write the name of the function followed by arguments in parentheses. For example, `atan2(y + z, 1)' is a call to the function `atan2', with two arguments. Whitespace is ignored between the built-in function name and the open-parenthesis, but we recommend that you avoid using whitespace there. User-defined functions do not permit whitespace in this way, and you will find it easier to avoid mistakes by following a simple convention which always works: no whitespace after a function name. Each built-in function accepts a certain number of arguments. In some cases, arguments can be omitted. The defaults for omitted arguments vary from function to function and are described under the individual functions. In some `awk' implementations, extra arguments given to built-in functions are ignored. However, in `gawk', it is a fatal error to give extra arguments to a built-in function. When a function is called, expressions that create the function's actual parameters are evaluated completely before the function call is performed. For example, in the code fragment: i = 4 j = sqrt(i++) the variable `i' is set to five before `sqrt' is called with a value of four for its actual parameter. The order of evaluation of the expressions used for the function's parameters is undefined. Thus, you should not write programs that assume that parameters are evaluated from left to right or from right to left. For example, i = 5 j = atan2(i++, i *= 2) If the order of evaluation is left to right, then `i' first becomes six, and then 12, and `atan2' is called with the two arguments six and 12. But if the order of evaluation is right to left, `i' first becomes 10, and then 11, and `atan2' is called with the two arguments 11 and 10.  File: gawk.info, Node: Numeric Functions, Next: String Functions, Prev: Calling Built-in, Up: Built-in Numeric Built-in Functions ========================== Here is a full list of built-in functions that work with numbers. Optional parameters are enclosed in square brackets ("[" and "]"). `int(X)' This produces the nearest integer to X, located between X and zero, truncated toward zero. For example, `int(3)' is three, `int(3.9)' is three, `int(-3.9)' is -3, and `int(-3)' is -3 as well. `sqrt(X)' This gives you the positive square root of X. It reports an error if X is negative. Thus, `sqrt(4)' is two. `exp(X)' This gives you the exponential of X (`e ^ X'), or reports an error if X is out of range. The range of values X can have depends on your machine's floating point representation. `log(X)' This gives you the natural logarithm of X, if X is positive; otherwise, it reports an error. `sin(X)' This gives you the sine of X, with X in radians. `cos(X)' This gives you the cosine of X, with X in radians. `atan2(Y, X)' This gives you the arctangent of `Y / X' in radians. `rand()' This gives you a random number. The values of `rand' are uniformly-distributed between zero and one. The value is never zero and never one. Often you want random integers instead. Here is a user-defined function you can use to obtain a random non-negative integer less than N: function randint(n) { return int(n * rand()) } The multiplication produces a random real number greater than zero and less than `n'. We then make it an integer (using `int') between zero and `n' - 1, inclusive. Here is an example where a similar function is used to produce random integers between one and N. This program prints a new random number for each input record. awk ' # Function to roll a simulated die. function roll(n) { return 1 + int(rand() * n) } # Roll 3 six-sided dice and # print total number of points. { printf("%d points\n", roll(6)+roll(6)+roll(6)) }' *Caution:* In most `awk' implementations, including `gawk', `rand' starts generating numbers from the same starting number, or "seed", each time you run `awk'. Thus, a program will generate the same results each time you run it. The numbers are random within one `awk' run, but predictable from run to run. This is convenient for debugging, but if you want a program to do different things each time it is used, you must change the seed to a value that will be different in each run. To do this, use `srand'. `srand([X])' The function `srand' sets the starting point, or seed, for generating random numbers to the value X. Each seed value leads to a particular sequence of random numbers.(1) Thus, if you set the seed to the same value a second time, you will get the same sequence of random numbers again. If you omit the argument X, as in `srand()', then the current date and time of day are used for a seed. This is the way to get random numbers that are truly unpredictable. The return value of `srand' is the previous seed. This makes it easy to keep track of the seeds for use in consistently reproducing sequences of random numbers. ---------- Footnotes ---------- (1) Computer generated random numbers really are not truly random. They are technically known as "pseudo-random." This means that while the numbers in a sequence appear to be random, you can in fact generate the same sequence of random numbers over and over again.  File: gawk.info, Node: String Functions, Next: I/O Functions, Prev: Numeric Functions, Up: Built-in Built-in Functions for String Manipulation ========================================== The functions in this section look at or change the text of one or more strings. Optional parameters are enclosed in square brackets ("[" and "]"). `index(IN, FIND)' This searches the string IN for the first occurrence of the string FIND, and returns the position in characters where that occurrence begins in the string IN. For example: $ awk 'BEGIN { print index("peanut", "an") }' -| 3 If FIND is not found, `index' returns zero. (Remember that string indices in `awk' start at one.) `length([STRING])' This gives you the number of characters in STRING. If STRING is a number, the length of the digit string representing that number is returned. For example, `length("abcde")' is five. By contrast, `length(15 * 35)' works out to three. How? Well, 15 * 35 = 525, and 525 is then converted to the string `"525"', which has three characters. If no argument is supplied, `length' returns the length of `$0'. In older versions of `awk', you could call the `length' function without any parentheses. Doing so is marked as "deprecated" in the POSIX standard. This means that while you can do this in your programs, it is a feature that can eventually be removed from a future version of the standard. Therefore, for maximal portability of your `awk' programs, you should always supply the parentheses. `match(STRING, REGEXP)' The `match' function searches the string, STRING, for the longest, leftmost substring matched by the regular expression, REGEXP. It returns the character position, or "index", of where that substring begins (one, if it starts at the beginning of STRING). If no match is found, it returns zero. The `match' function sets the built-in variable `RSTART' to the index. It also sets the built-in variable `RLENGTH' to the length in characters of the matched substring. If no match is found, `RSTART' is set to zero, and `RLENGTH' to -1. For example: awk '{ if ($1 == "FIND") regex = $2 else { where = match($0, regex) if (where != 0) print "Match of", regex, "found at", \ where, "in", $0 } }' This program looks for lines that match the regular expression stored in the variable `regex'. This regular expression can be changed. If the first word on a line is `FIND', `regex' is changed to be the second word on that line. Therefore, given: FIND ru+n My program runs but not very quickly FIND Melvin JF+KM This line is property of Reality Engineering Co. Melvin was here. `awk' prints: Match of ru+n found at 12 in My program runs Match of Melvin found at 1 in Melvin was here. `split(STRING, ARRAY [, FIELDSEP])' This divides STRING into pieces separated by FIELDSEP, and stores the pieces in ARRAY. The first piece is stored in `ARRAY[1]', the second piece in `ARRAY[2]', and so forth. The string value of the third argument, FIELDSEP, is a regexp describing where to split STRING (much as `FS' can be a regexp describing where to split input records). If the FIELDSEP is omitted, the value of `FS' is used. `split' returns the number of elements created. The `split' function splits strings into pieces in a manner similar to the way input lines are split into fields. For example: split("cul-de-sac", a, "-") splits the string `cul-de-sac' into three fields using `-' as the separator. It sets the contents of the array `a' as follows: a[1] = "cul" a[2] = "de" a[3] = "sac" The value returned by this call to `split' is three. As with input field-splitting, when the value of FIELDSEP is `" "', leading and trailing whitespace is ignored, and the elements are separated by runs of whitespace. Also as with input field-splitting, if FIELDSEP is the null string, each individual character in the string is split into its own array element. (This is a `gawk'-specific extension.) Recent implementations of `awk', including `gawk', allow the third argument to be a regexp constant (`/abc/'), as well as a string (d.c.). The POSIX standard allows this as well. Before splitting the string, `split' deletes any previously existing elements in the array ARRAY (d.c.). `sprintf(FORMAT, EXPRESSION1,...)' This returns (without printing) the string that `printf' would have printed out with the same arguments (*note Using `printf' Statements for Fancier Printing: Printf.). For example: sprintf("pi = %.2f (approx.)", 22/7) returns the string `"pi = 3.14 (approx.)"'. `sub(REGEXP, REPLACEMENT [, TARGET])' The `sub' function alters the value of TARGET. It searches this value, which is treated as a string, for the leftmost longest substring matched by the regular expression, REGEXP, extending this match as far as possible. Then the entire string is changed by replacing the matched text with REPLACEMENT. The modified string becomes the new value of TARGET. This function is peculiar because TARGET is not simply used to compute a value, and not just any expression will do: it must be a variable, field or array element, so that `sub' can store a modified value there. If this argument is omitted, then the default is to use and alter `$0'. For example: str = "water, water, everywhere" sub(/at/, "ith", str) sets `str' to `"wither, water, everywhere"', by replacing the leftmost, longest occurrence of `at' with `ith'. The `sub' function returns the number of substitutions made (either one or zero). If the special character `&' appears in REPLACEMENT, it stands for the precise substring that was matched by REGEXP. (If the regexp can match more than one string, then this precise substring may vary.) For example: awk '{ sub(/candidate/, "& and his wife"); print }' changes the first occurrence of `candidate' to `candidate and his wife' on each input line. Here is another example: awk 'BEGIN { str = "daabaaa" sub(/a*/, "c&c", str) print str }' -| dcaacbaaa This shows how `&' can represent a non-constant string, and also illustrates the "leftmost, longest" rule in regexp matching (*note How Much Text Matches?: Leftmost Longest.). The effect of this special character (`&') can be turned off by putting a backslash before it in the string. As usual, to insert one backslash in the string, you must write two backslashes. Therefore, write `\\&' in a string constant to include a literal `&' in the replacement. For example, here is how to replace the first `|' on each line with an `&': awk '{ sub(/\|/, "\\&"); print }' *Note:* As mentioned above, the third argument to `sub' must be a variable, field or array reference. Some versions of `awk' allow the third argument to be an expression which is not an lvalue. In such a case, `sub' would still search for the pattern and return zero or one, but the result of the substitution (if any) would be thrown away because there is no place to put it. Such versions of `awk' accept expressions like this: sub(/USA/, "United States", "the USA and Canada") For historical compatibility, `gawk' will accept erroneous code, such as in the above example. However, using any other non-changeable object as the third parameter will cause a fatal error, and your program will not run. `gsub(REGEXP, REPLACEMENT [, TARGET])' This is similar to the `sub' function, except `gsub' replaces *all* of the longest, leftmost, *non-overlapping* matching substrings it can find. The `g' in `gsub' stands for "global," which means replace everywhere. For example: awk '{ gsub(/Britain/, "United Kingdom"); print }' replaces all occurrences of the string `Britain' with `United Kingdom' for all input records. The `gsub' function returns the number of substitutions made. If the variable to be searched and altered, TARGET, is omitted, then the entire input record, `$0', is used. As in `sub', the characters `&' and `\' are special, and the third argument must be an lvalue. `gensub(REGEXP, REPLACEMENT, HOW [, TARGET])' `gensub' is a general substitution function. Like `sub' and `gsub', it searches the target string TARGET for matches of the regular expression REGEXP. Unlike `sub' and `gsub', the modified string is returned as the result of the function, and the original target string is *not* changed. If HOW is a string beginning with `g' or `G', then it replaces all matches of REGEXP with REPLACEMENT. Otherwise, HOW is a number indicating which match of REGEXP to replace. If no TARGET is supplied, `$0' is used instead. `gensub' provides an additional feature that is not available in `sub' or `gsub': the ability to specify components of a regexp in the replacement text. This is done by using parentheses in the regexp to mark the components, and then specifying `\N' in the replacement text, where N is a digit from one to nine. For example: $ gawk ' > BEGIN { > a = "abc def" > b = gensub(/(.+) (.+)/, "\\2 \\1", "g", a) > print b > }' -| def abc As described above for `sub', you must type two backslashes in order to get one into the string. In the replacement text, the sequence `\0' represents the entire matched text, as does the character `&'. This example shows how you can use the third argument to control which match of the regexp should be changed. $ echo a b c a b c | > gawk '{ print gensub(/a/, "AA", 2) }' -| a b c AA b c In this case, `$0' is used as the default target string. `gensub' returns the new string as its result, which is passed directly to `print' for printing. If the HOW argument is a string that does not begin with `g' or `G', or if it is a number that is less than zero, only one substitution is performed. `gensub' is a `gawk' extension; it is not available in compatibility mode (*note Command Line Options: Options.). `substr(STRING, START [, LENGTH])' This returns a LENGTH-character-long substring of STRING, starting at character number START. The first character of a string is character number one. For example, `substr("washington", 5, 3)' returns `"ing"'. If LENGTH is not present, this function returns the whole suffix of STRING that begins at character number START. For example, `substr("washington", 5)' returns `"ington"'. The whole suffix is also returned if LENGTH is greater than the number of characters remaining in the string, counting from character number START. *Note:* The string returned by `substr' *cannot* be assigned to. Thus, it is a mistake to attempt to change a portion of a string, like this: string = "abcdef" # try to get "abCDEf", won't work substr(string, 3, 3) = "CDE" or to use `substr' as the third agument of `sub' or `gsub': gsub(/xyz/, "pdq", substr($0, 5, 20)) # WRONG `tolower(STRING)' This returns a copy of STRING, with each upper-case character in the string replaced with its corresponding lower-case character. Non-alphabetic characters are left unchanged. For example, `tolower("MiXeD cAsE 123")' returns `"mixed case 123"'. `toupper(STRING)' This returns a copy of STRING, with each lower-case character in the string replaced with its corresponding upper-case character. Non-alphabetic characters are left unchanged. For example, `toupper("MiXeD cAsE 123")' returns `"MIXED CASE 123"'. More About `\' and `&' with `sub', `gsub' and `gensub' ------------------------------------------------------ When using `sub', `gsub' or `gensub', and trying to get literal backslashes and ampersands into the replacement text, you need to remember that there are several levels of "escape processing" going on. First, there is the "lexical" level, which is when `awk' reads your program, and builds an internal copy of your program that can be executed. Then there is the run-time level, when `awk' actually scans the replacement string to determine what to generate. At both levels, `awk' looks for a defined set of characters that can come after a backslash. At the lexical level, it looks for the escape sequences listed in *Note Escape Sequences::. Thus, for every `\' that `awk' will process at the run-time level, you type two `\'s at the lexical level. When a character that is not valid for an escape sequence follows the `\', Unix `awk' and `gawk' both simply remove the initial `\', and put the following character into the string. Thus, for example, `"a\qb"' is treated as `"aqb"'. At the run-time level, the various functions handle sequences of `\' and `&' differently. The situation is (sadly) somewhat complex. Historically, the `sub' and `gsub' functions treated the two character sequence `\&' specially; this sequence was replaced in the generated text with a single `&'. Any other `\' within the REPLACEMENT string that did not precede an `&' was passed through unchanged. To illustrate with a table: You type `sub' sees `sub' generates -------- ---------- --------------- `\&' `&' the matched text `\\&' `\&' a literal `&' `\\\&' `\&' a literal `&' `\\\\&' `\\&' a literal `\&' `\\\\\&' `\\&' a literal `\&' `\\\\\\&' `\\\&' a literal `\\&' `\\q' `\q' a literal `\q' This table shows both the lexical level processing, where an odd number of backslashes becomes an even number at the run time level, and the run-time processing done by `sub'. (For the sake of simplicity, the rest of the tables below only show the case of even numbers of `\'s entered at the lexical level.) The problem with the historical approach is that there is no way to get a literal `\' followed by the matched text. The 1992 POSIX standard attempted to fix this problem. The standard says that `sub' and `gsub' look for either a `\' or an `&' after the `\'. If either one follows a `\', that character is output literally. The interpretation of `\' and `&' then becomes like this: You type `sub' sees `sub' generates -------- ---------- --------------- `&' `&' the matched text `\\&' `\&' a literal `&' `\\\\&' `\\&' a literal `\', then the matched text `\\\\\\&' `\\\&' a literal `\&' This would appear to solve the problem. Unfortunately, the phrasing of the standard is unusual. It says, in effect, that `\' turns off the special meaning of any following character, but that for anything other than `\' and `&', such special meaning is undefined. This wording leads to two problems. 1. Backslashes must now be doubled in the REPLACEMENT string, breaking historical `awk' programs. 2. To make sure that an `awk' program is portable, *every* character in the REPLACEMENT string must be preceded with a backslash.(1) The POSIX standard is under revision.(2) Because of the above problems, proposed text for the revised standard reverts to rules that correspond more closely to the original existing practice. The proposed rules have special cases that make it possible to produce a `\' preceding the matched text. You type `sub' sees `sub' generates -------- ---------- --------------- `\\\\\\&' `\\\&' a literal `\&' `\\\\&' `\\&' a literal `\', followed by the matched text `\\&' `\&' a literal `&' `\\q' `\q' a literal `\q' In a nutshell, at the run-time level, there are now three special sequences of characters, `\\\&', `\\&' and `\&', whereas historically, there was only one. However, as in the historical case, any `\' that is not part of one of these three sequences is not special, and appears in the output literally. `gawk' 3.0 follows these proposed POSIX rules for `sub' and `gsub'. Whether these proposed rules will actually become codified into the standard is unknown at this point. Subsequent `gawk' releases will track the standard and implement whatever the final version specifies; this Info file will be updated as well. The rules for `gensub' are considerably simpler. At the run-time level, whenever `gawk' sees a `\', if the following character is a digit, then the text that matched the corresponding parenthesized subexpression is placed in the generated output. Otherwise, no matter what the character after the `\' is, that character will appear in the generated text, and the `\' will not. You type `gensub' sees `gensub' generates -------- ------------- ------------------ `&' `&' the matched text `\\&' `\&' a literal `&' `\\\\' `\\' a literal `\' `\\\\&' `\\&' a literal `\', then the matched text `\\\\\\&' `\\\&' a literal `\&' `\\q' `\q' a literal `q' Because of the complexity of the lexical and run-time level processing, and the special cases for `sub' and `gsub', we recommend the use of `gawk' and `gensub' for when you have to do substitutions. ---------- Footnotes ---------- (1) This consequence was certainly unintended. (2) As of February 1997, with final approval and publication hopefully sometime in 1997.  File: gawk.info, Node: I/O Functions, Next: Time Functions, Prev: String Functions, Up: Built-in Built-in Functions for Input/Output =================================== The following functions are related to Input/Output (I/O). Optional parameters are enclosed in square brackets ("[" and "]"). `close(FILENAME)' Close the file FILENAME, for input or output. The argument may alternatively be a shell command that was used for redirecting to or from a pipe; then the pipe is closed. *Note Closing Input and Output Files and Pipes: Close Files And Pipes, for more information. `fflush([FILENAME])' Flush any buffered output associated FILENAME, which is either a file opened for writing, or a shell command for redirecting output to a pipe. Many utility programs will "buffer" their output; they save information to be written to a disk file or terminal in memory, until there is enough for it to be worthwhile to send the data to the ouput device. This is often more efficient than writing every little bit of information as soon as it is ready. However, sometimes it is necessary to force a program to "flush" its buffers; that is, write the information to its destination, even if a buffer is not full. This is the purpose of the `fflush' function; `gawk' too buffers its output, and the `fflush' function can be used to force `gawk' to flush its buffers. `fflush' is a recent (1994) addition to the Bell Labs research version of `awk'; it is not part of the POSIX standard, and will not be available if `--posix' has been specified on the command line (*note Command Line Options: Options.). `gawk' extends the `fflush' function in two ways. The first is to allow no argument at all. In this case, the buffer for the standard output is flushed. The second way is to allow the null string (`""') as the argument. In this case, the buffers for *all* open output files and pipes are flushed. `fflush' returns zero if the buffer was successfully flushed, and nonzero otherwise. `system(COMMAND)' The system function allows the user to execute operating system commands and then return to the `awk' program. The `system' function executes the command given by the string COMMAND. It returns, as its value, the status returned by the command that was executed. For example, if the following fragment of code is put in your `awk' program: END { system("date | mail -s 'awk run done' root") } the system administrator will be sent mail when the `awk' program finishes processing input and begins its end-of-input processing. Note that redirecting `print' or `printf' into a pipe is often enough to accomplish your task. However, if your `awk' program is interactive, `system' is useful for cranking up large self-contained programs, such as a shell or an editor. Some operating systems cannot implement the `system' function. `system' causes a fatal error if it is not supported. Interactive vs. Non-Interactive Buffering ----------------------------------------- As a side point, buffering issues can be even more confusing depending upon whether or not your program is "interactive", i.e., communicating with a user sitting at a keyboard.(1) Interactive programs generally "line buffer" their output; they write out every line. Non-interactive programs wait until they have a full buffer, which may be many lines of output. Here is an example of the difference. $ awk '{ print $1 + $2 }' 1 1 -| 2 2 3 -| 5 Control-d Each line of output is printed immediately. Compare that behavior with this example. $ awk '{ print $1 + $2 }' | cat 1 1 2 3 Control-d -| 2 -| 5 Here, no output is printed until after the `Control-d' is typed, since it is all buffered, and sent down the pipe to `cat' in one shot. Controlling Output Buffering with `system' ------------------------------------------ The `fflush' function provides explicit control over output buffering for individual files and pipes. However, its use is not portable to many other `awk' implementations. An alternative method to flush output buffers is by calling `system' with a null string as its argument: system("") # flush output `gawk' treats this use of the `system' function as a special case, and is smart enough not to run a shell (or other command interpreter) with the empty command. Therefore, with `gawk', this idiom is not only useful, it is efficient. While this method should work with other `awk' implementations, it will not necessarily avoid starting an unnecessary shell. (Other implementations may only flush the buffer associated with the standard output, and not necessarily all buffered output.) If you think about what a programmer expects, it makes sense that `system' should flush any pending output. The following program: BEGIN { print "first print" system("echo system echo") print "second print" } must print first print system echo second print and not system echo first print second print If `awk' did not flush its buffers before calling `system', the latter (undesirable) output is what you would see. ---------- Footnotes ---------- (1) A program is interactive if the standard output is connected to a terminal device.  File: gawk.info, Node: Time Functions, Prev: I/O Functions, Up: Built-in Functions for Dealing with Time Stamps ====================================== A common use for `awk' programs is the processing of log files containing time stamp information, indicating when a particular log record was written. Many programs log their time stamp in the form returned by the `time' system call, which is the number of seconds since a particular epoch. On POSIX systems, it is the number of seconds since Midnight, January 1, 1970, UTC. In order to make it easier to process such log files, and to produce useful reports, `gawk' provides two functions for working with time stamps. Both of these are `gawk' extensions; they are not specified in the POSIX standard, nor are they in any other known version of `awk'. Optional parameters are enclosed in square brackets ("[" and "]"). `systime()' This function returns the current time as the number of seconds since the system epoch. On POSIX systems, this is the number of seconds since Midnight, January 1, 1970, UTC. It may be a different number on other systems. `strftime([FORMAT [, TIMESTAMP]])' This function returns a string. It is similar to the function of the same name in ANSI C. The time specified by TIMESTAMP is used to produce a string, based on the contents of the FORMAT string. The TIMESTAMP is in the same format as the value returned by the `systime' function. If no TIMESTAMP argument is supplied, `gawk' will use the current time of day as the time stamp. If no FORMAT argument is supplied, `strftime' uses `"%a %b %d %H:%M:%S %Z %Y"'. This format string produces output (almost) equivalent to that of the `date' utility. (Versions of `gawk' prior to 3.0 require the FORMAT argument.) The `systime' function allows you to compare a time stamp from a log file with the current time of day. In particular, it is easy to determine how long ago a particular record was logged. It also allows you to produce log records using the "seconds since the epoch" format. The `strftime' function allows you to easily turn a time stamp into human-readable information. It is similar in nature to the `sprintf' function (*note Built-in Functions for String Manipulation: String Functions.), in that it copies non-format specification characters verbatim to the returned string, while substituting date and time values for format specifications in the FORMAT string. `strftime' is guaranteed by the ANSI C standard to support the following date format specifications: `%a' The locale's abbreviated weekday name. `%A' The locale's full weekday name. `%b' The locale's abbreviated month name. `%B' The locale's full month name. `%c' The locale's "appropriate" date and time representation. `%d' The day of the month as a decimal number (01-31). `%H' The hour (24-hour clock) as a decimal number (00-23). `%I' The hour (12-hour clock) as a decimal number (01-12). `%j' The day of the year as a decimal number (001-366). `%m' The month as a decimal number (01-12). `%M' The minute as a decimal number (00-59). `%p' The locale's equivalent of the AM/PM designations associated with a 12-hour clock. `%S' The second as a decimal number (00-60).(1) `%U' The week number of the year (the first Sunday as the first day of week one) as a decimal number (00-53). `%w' The weekday as a decimal number (0-6). Sunday is day zero. `%W' The week number of the year (the first Monday as the first day of week one) as a decimal number (00-53). `%x' The locale's "appropriate" date representation. `%X' The locale's "appropriate" time representation. `%y' The year without century as a decimal number (00-99). `%Y' The year with century as a decimal number (e.g., 1995). `%Z' The time zone name or abbreviation, or no characters if no time zone is determinable. `%%' A literal `%'. If a conversion specifier is not one of the above, the behavior is undefined.(2) Informally, a "locale" is the geographic place in which a program is meant to run. For example, a common way to abbreviate the date September 4, 1991 in the United States would be "9/4/91". In many countries in Europe, however, it would be abbreviated "4.9.91". Thus, the `%x' specification in a `"US"' locale might produce `9/4/91', while in a `"EUROPE"' locale, it might produce `4.9.91'. The ANSI C standard defines a default `"C"' locale, which is an environment that is typical of what most C programmers are used to. A public-domain C version of `strftime' is supplied with `gawk' for systems that are not yet fully ANSI-compliant. If that version is used to compile `gawk' (*note Installing `gawk': Installation.), then the following additional format specifications are available: `%D' Equivalent to specifying `%m/%d/%y'. `%e' The day of the month, padded with a space if it is only one digit. `%h' Equivalent to `%b', above. `%n' A newline character (ASCII LF). `%r' Equivalent to specifying `%I:%M:%S %p'. `%R' Equivalent to specifying `%H:%M'. `%T' Equivalent to specifying `%H:%M:%S'. `%t' A tab character. `%k' The hour (24-hour clock) as a decimal number (0-23). Single digit numbers are padded with a space. `%l' The hour (12-hour clock) as a decimal number (1-12). Single digit numbers are padded with a space. `%C' The century, as a number between 00 and 99. `%u' The weekday as a decimal number [1 (Monday)-7]. `%V' The week number of the year (the first Monday as the first day of week one) as a decimal number (01-53). The method for determining the week number is as specified by ISO 8601 (to wit: if the week containing January 1 has four or more days in the new year, then it is week one, otherwise it is week 53 of the previous year and the next week is week one). `%G' The year with century of the ISO week number, as a decimal number. For example, January 1, 1993, is in week 53 of 1992. Thus, the year of its ISO week number is 1992, even though its year is 1993. Similarly, December 31, 1973, is in week 1 of 1974. Thus, the year of its ISO week number is 1974, even though its year is 1973. `%g' The year without century of the ISO week number, as a decimal number (00-99). `%Ec %EC %Ex %Ey %EY %Od %Oe %OH %OI' `%Om %OM %OS %Ou %OU %OV %Ow %OW %Oy' These are "alternate representations" for the specifications that use only the second letter (`%c', `%C', and so on). They are recognized, but their normal representations are used.(3) (These facilitate compliance with the POSIX `date' utility.) `%v' The date in VMS format (e.g., 20-JUN-1991). `%z' The timezone offset in a +HHMM format (e.g., the format necessary to produce RFC-822/RFC-1036 date headers). This example is an `awk' implementation of the POSIX `date' utility. Normally, the `date' utility prints the current date and time of day in a well known format. However, if you provide an argument to it that begins with a `+', `date' will copy non-format specifier characters to the standard output, and will interpret the current time according to the format specifiers in the string. For example: $ date '+Today is %A, %B %d, %Y.' -| Today is Thursday, July 11, 1991. Here is the `gawk' version of the `date' utility. It has a shell "wrapper", to handle the `-u' option, which requires that `date' run as if the time zone was set to UTC. #! /bin/sh # # date --- approximate the P1003.2 'date' command case $1 in -u) TZ=GMT0 # use UTC export TZ shift ;; esac gawk 'BEGIN { format = "%a %b %d %H:%M:%S %Z %Y" exitval = 0 if (ARGC > 2) exitval = 1 else if (ARGC == 2) { format = ARGV[1] if (format ~ /^\+/) format = substr(format, 2) # remove leading + } print strftime(format) exit exitval }' "$@@" ---------- Footnotes ---------- (1) Occasionally there are minutes in a year with a leap second, which is why the seconds can go up to 60. (2) This is because ANSI C leaves the behavior of the C version of `strftime' undefined, and `gawk' will use the system's version of `strftime' if it's there. Typically, the conversion specifier will either not appear in the returned string, or it will appear literally. (3) If you don't understand any of this, don't worry about it; these facilities are meant to make it easier to "internationalize" programs.  File: gawk.info, Node: User-defined, Next: Invoking Gawk, Prev: Built-in, Up: Top User-defined Functions ********************** Complicated `awk' programs can often be simplified by defining your own functions. User-defined functions can be called just like built-in ones (*note Function Calls::.), but it is up to you to define them--to tell `awk' what they should do. * Menu: * Definition Syntax:: How to write definitions and what they mean. * Function Example:: An example function definition and what it does. * Function Caveats:: Things to watch out for. * Return Statement:: Specifying the value a function returns.  File: gawk.info, Node: Definition Syntax, Next: Function Example, Prev: User-defined, Up: User-defined Function Definition Syntax ========================== Definitions of functions can appear anywhere between the rules of an `awk' program. Thus, the general form of an `awk' program is extended to include sequences of rules *and* user-defined function definitions. There is no need in `awk' to put the definition of a function before all uses of the function. This is because `awk' reads the entire program before starting to execute any of it. The definition of a function named NAME looks like this: function NAME(PARAMETER-LIST) { BODY-OF-FUNCTION } NAME is the name of the function to be defined. A valid function name is like a valid variable name: a sequence of letters, digits and underscores, not starting with a digit. Within a single `awk' program, any particular name can only be used as a variable, array or function. PARAMETER-LIST is a list of the function's arguments and local variable names, separated by commas. When the function is called, the argument names are used to hold the argument values given in the call. The local variables are initialized to the empty string. A function cannot have two parameters with the same name. The BODY-OF-FUNCTION consists of `awk' statements. It is the most important part of the definition, because it says what the function should actually *do*. The argument names exist to give the body a way to talk about the arguments; local variables, to give the body places to keep temporary values. Argument names are not distinguished syntactically from local variable names; instead, the number of arguments supplied when the function is called determines how many argument variables there are. Thus, if three argument values are given, the first three names in PARAMETER-LIST are arguments, and the rest are local variables. It follows that if the number of arguments is not the same in all calls to the function, some of the names in PARAMETER-LIST may be arguments on some occasions and local variables on others. Another way to think of this is that omitted arguments default to the null string. Usually when you write a function you know how many names you intend to use for arguments and how many you intend to use as local variables. It is conventional to place some extra space between the arguments and the local variables, to document how your function is supposed to be used. During execution of the function body, the arguments and local variable values hide or "shadow" any variables of the same names used in the rest of the program. The shadowed variables are not accessible in the function definition, because there is no way to name them while their names have been taken away for the local variables. All other variables used in the `awk' program can be referenced or set normally in the function's body. The arguments and local variables last only as long as the function body is executing. Once the body finishes, you can once again access the variables that were shadowed while the function was running. The function body can contain expressions which call functions. They can even call this function, either directly or by way of another function. When this happens, we say the function is "recursive". In many `awk' implementations, including `gawk', the keyword `function' may be abbreviated `func'. However, POSIX only specifies the use of the keyword `function'. This actually has some practical implications. If `gawk' is in POSIX-compatibility mode (*note Command Line Options: Options.), then the following statement will *not* define a function: func foo() { a = sqrt($1) ; print a } Instead it defines a rule that, for each record, concatenates the value of the variable `func' with the return value of the function `foo'. If the resulting string is non-null, the action is executed. This is probably not what was desired. (`awk' accepts this input as syntactically valid, since functions may be used before they are defined in `awk' programs.) To ensure that your `awk' programs are portable, always use the keyword `function' when defining a function.  File: gawk.info, Node: Function Example, Next: Function Caveats, Prev: Definition Syntax, Up: User-defined Function Definition Examples ============================ Here is an example of a user-defined function, called `myprint', that takes a number and prints it in a specific format. function myprint(num) { printf "%6.3g\n", num } To illustrate, here is an `awk' rule which uses our `myprint' function: $3 > 0 { myprint($3) } This program prints, in our special format, all the third fields that contain a positive number in our input. Therefore, when given: 1.2 3.4 5.6 7.8 9.10 11.12 -13.14 15.16 17.18 19.20 21.22 23.24 this program, using our function to format the results, prints: 5.6 21.2 This function deletes all the elements in an array. function delarray(a, i) { for (i in a) delete a[i] } When working with arrays, it is often necessary to delete all the elements in an array and start over with a new list of elements (*note The `delete' Statement: Delete.). Instead of having to repeat this loop everywhere in your program that you need to clear out an array, your program can just call `delarray'. Here is an example of a recursive function. It takes a string as an input parameter, and returns the string in backwards order. function rev(str, start) { if (start == 0) return "" return (substr(str, start, 1) rev(str, start - 1)) } If this function is in a file named `rev.awk', we can test it this way: $ echo "Don't Panic!" | > gawk --source '{ print rev($0, length($0)) }' -f rev.awk -| !cinaP t'noD Here is an example that uses the built-in function `strftime'. (*Note Functions for Dealing with Time Stamps: Time Functions, for more information on `strftime'.) The C `ctime' function takes a timestamp and returns it in a string, formatted in a well known fashion. Here is an `awk' version: # ctime.awk # # awk version of C ctime(3) function function ctime(ts, format) { format = "%a %b %d %H:%M:%S %Z %Y" if (ts == 0) ts = systime() # use current time as default return strftime(format, ts) }  File: gawk.info, Node: Function Caveats, Next: Return Statement, Prev: Function Example, Up: User-defined Calling User-defined Functions ============================== "Calling a function" means causing the function to run and do its job. A function call is an expression, and its value is the value returned by the function. A function call consists of the function name followed by the arguments in parentheses. What you write in the call for the arguments are `awk' expressions; each time the call is executed, these expressions are evaluated, and the values are the actual arguments. For example, here is a call to `foo' with three arguments (the first being a string concatenation): foo(x y, "lose", 4 * z) *Caution:* whitespace characters (spaces and tabs) are not allowed between the function name and the open-parenthesis of the argument list. If you write whitespace by mistake, `awk' might think that you mean to concatenate a variable with an expression in parentheses. However, it notices that you used a function name and not a variable name, and reports an error. When a function is called, it is given a *copy* of the values of its arguments. This is known as "call by value". The caller may use a variable as the expression for the argument, but the called function does not know this: it only knows what value the argument had. For example, if you write this code: foo = "bar" z = myfunc(foo) then you should not think of the argument to `myfunc' as being "the variable `foo'." Instead, think of the argument as the string value, `"bar"'. If the function `myfunc' alters the values of its local variables, this has no effect on any other variables. Thus, if `myfunc' does this: function myfunc(str) { print str str = "zzz" print str } to change its first argument variable `str', this *does not* change the value of `foo' in the caller. The role of `foo' in calling `myfunc' ended when its value, `"bar"', was computed. If `str' also exists outside of `myfunc', the function body cannot alter this outer value, because it is shadowed during the execution of `myfunc' and cannot be seen or changed from there. However, when arrays are the parameters to functions, they are *not* copied. Instead, the array itself is made available for direct manipulation by the function. This is usually called "call by reference". Changes made to an array parameter inside the body of a function *are* visible outside that function. This can be *very* dangerous if you do not watch what you are doing. For example: function changeit(array, ind, nvalue) { array[ind] = nvalue } BEGIN { a[1] = 1; a[2] = 2; a[3] = 3 changeit(a, 2, "two") printf "a[1] = %s, a[2] = %s, a[3] = %s\n", a[1], a[2], a[3] } This program prints `a[1] = 1, a[2] = two, a[3] = 3', because `changeit' stores `"two"' in the second element of `a'. Some `awk' implementations allow you to call a function that has not been defined, and only report a problem at run-time when the program actually tries to call the function. For example: BEGIN { if (0) foo() else bar() } function bar() { ... } # note that `foo' is not defined Since the `if' statement will never be true, it is not really a problem that `foo' has not been defined. Usually though, it is a problem if a program calls an undefined function. If `--lint' has been specified (*note Command Line Options: Options.), `gawk' will report about calls to undefined functions. Some `awk' implementations generate a run-time error if you use the `next' statement (*note The `next' Statement: Next Statement.) inside a user-defined function. `gawk' does not have this problem.  File: gawk.info, Node: Return Statement, Prev: Function Caveats, Up: User-defined The `return' Statement ====================== The body of a user-defined function can contain a `return' statement. This statement returns control to the rest of the `awk' program. It can also be used to return a value for use in the rest of the `awk' program. It looks like this: return [EXPRESSION] The EXPRESSION part is optional. If it is omitted, then the returned value is undefined and, therefore, unpredictable. A `return' statement with no value expression is assumed at the end of every function definition. So if control reaches the end of the function body, then the function returns an unpredictable value. `awk' will *not* warn you if you use the return value of such a function. Sometimes, you want to write a function for what it does, not for what it returns. Such a function corresponds to a `void' function in C or to a `procedure' in Pascal. Thus, it may be appropriate to not return any value; you should simply bear in mind that if you use the return value of such a function, you do so at your own risk. Here is an example of a user-defined function that returns a value for the largest number among the elements of an array: function maxelt(vec, i, ret) { for (i in vec) { if (ret == "" || vec[i] > ret) ret = vec[i] } return ret } You call `maxelt' with one argument, which is an array name. The local variables `i' and `ret' are not intended to be arguments; while there is nothing to stop you from passing two or three arguments to `maxelt', the results would be strange. The extra space before `i' in the function parameter list indicates that `i' and `ret' are not supposed to be arguments. This is a convention that you should follow when you define functions. Here is a program that uses our `maxelt' function. It loads an array, calls `maxelt', and then reports the maximum number in that array: awk ' function maxelt(vec, i, ret) { for (i in vec) { if (ret == "" || vec[i] > ret) ret = vec[i] } return ret } # Load all fields of each record into nums. { for(i = 1; i <= NF; i++) nums[NR, i] = $i } END { print maxelt(nums) }' Given the following input: 1 5 23 8 16 44 3 5 2 8 26 256 291 1396 2962 100 -6 467 998 1101 99385 11 0 225 our program tells us (predictably) that `99385' is the largest number in our array.  File: gawk.info, Node: Invoking Gawk, Next: Library Functions, Prev: User-defined, Up: Top Running `awk' ************* There are two ways to run `awk': with an explicit program, or with one or more program files. Here are templates for both of them; items enclosed in `[...]' in these templates are optional. Besides traditional one-letter POSIX-style options, `gawk' also supports GNU long options. awk [OPTIONS] -f progfile [`--'] FILE ... awk [OPTIONS] [`--'] 'PROGRAM' FILE ... It is possible to invoke `awk' with an empty program: $ awk '' datafile1 datafile2 Doing so makes little sense though; `awk' will simply exit silently when given an empty program (d.c.). If `--lint' has been specified on the command line, `gawk' will issue a warning that the program is empty. * Menu: * Options:: Command line options and their meanings. * Other Arguments:: Input file names and variable assignments. * AWKPATH Variable:: Searching directories for `awk' programs. * Obsolete:: Obsolete Options and/or features. * Undocumented:: Undocumented Options and Features. * Known Bugs:: Known Bugs in `gawk'.  File: gawk.info, Node: Options, Next: Other Arguments, Prev: Invoking Gawk, Up: Invoking Gawk Command Line Options ==================== Options begin with a dash, and consist of a single character. GNU style long options consist of two dashes and a keyword. The keyword can be abbreviated, as long the abbreviation allows the option to be uniquely identified. If the option takes an argument, then the keyword is either immediately followed by an equals sign (`=') and the argument's value, or the keyword and the argument's value are separated by whitespace. For brevity, the discussion below only refers to the traditional short options; however the long and short options are interchangeable in all contexts. Each long option for `gawk' has a corresponding POSIX-style option. The options and their meanings are as follows: `-F FS' `--field-separator FS' Sets the `FS' variable to FS (*note Specifying How Fields are Separated: Field Separators.). `-f SOURCE-FILE' `--file SOURCE-FILE' Indicates that the `awk' program is to be found in SOURCE-FILE instead of in the first non-option argument. `-v VAR=VAL' `--assign VAR=VAL' Sets the variable VAR to the value VAL *before* execution of the program begins. Such variable values are available inside the `BEGIN' rule (*note Other Command Line Arguments: Other Arguments.). The `-v' option can only set one variable, but you can use it more than once, setting another variable each time, like this: `awk -v foo=1 -v bar=2 ...'. `-mf NNN' `-mr NNN' Set various memory limits to the value NNN. The `f' flag sets the maximum number of fields, and the `r' flag sets the maximum record size. These two flags and the `-m' option are from the Bell Labs research version of Unix `awk'. They are provided for compatibility, but otherwise ignored by `gawk', since `gawk' has no predefined limits. `-W GAWK-OPT' Following the POSIX standard, options that are implementation specific are supplied as arguments to the `-W' option. These options also have corresponding GNU style long options. See below. `--' Signals the end of the command line options. The following arguments are not treated as options even if they begin with `-'. This interpretation of `--' follows the POSIX argument parsing conventions. This is useful if you have file names that start with `-', or in shell scripts, if you have file names that will be specified by the user which could start with `-'. The following `gawk'-specific options are available: `-W traditional' `-W compat' `--traditional' `--compat' Specifies "compatibility mode", in which the GNU extensions to the `awk' language are disabled, so that `gawk' behaves just like the Bell Labs research version of Unix `awk'. `--traditional' is the preferred form of this option. *Note Extensions in `gawk' Not in POSIX `awk': POSIX/GNU, which summarizes the extensions. Also see *Note Downward Compatibility and Debugging: Compatibility Mode. `-W copyleft' `-W copyright' `--copyleft' `--copyright' Print the short version of the General Public License, and then exit. This option may disappear in a future version of `gawk'. `-W help' `-W usage' `--help' `--usage' Print a "usage" message summarizing the short and long style options that `gawk' accepts, and then exit. `-W lint' `--lint' Warn about constructs that are dubious or non-portable to other `awk' implementations. Some warnings are issued when `gawk' first reads your program. Others are issued at run-time, as your program executes. `-W lint-old' `--lint-old' Warn about constructs that are not available in the original Version 7 Unix version of `awk' (*note Major Changes between V7 and SVR3.1: V7/SVR3.1.). `-W posix' `--posix' Operate in strict POSIX mode. This disables all `gawk' extensions (just like `--traditional'), and adds the following additional restrictions: * `\x' escape sequences are not recognized (*note Escape Sequences::.). * Newlines do not act as whitespace to separate fields when `FS' is equal to a single space. * The synonym `func' for the keyword `function' is not recognized (*note Function Definition Syntax: Definition Syntax.). * The operators `**' and `**=' cannot be used in place of `^' and `^=' (*note Arithmetic Operators: Arithmetic Ops., and also *note Assignment Expressions: Assignment Ops.). * Specifying `-Ft' on the command line does not set the value of `FS' to be a single tab character (*note Specifying How Fields are Separated: Field Separators.). * The `fflush' built-in function is not supported (*note Built-in Functions for Input/Output: I/O Functions.). If you supply both `--traditional' and `--posix' on the command line, `--posix' will take precedence. `gawk' will also issue a warning if both options are supplied. `-W re-interval' `--re-interval' Allow interval expressions (*note Regular Expression Operators: Regexp Operators.), in regexps. Because interval expressions were traditionally not available in `awk', `gawk' does not provide them by default. This prevents old `awk' programs from breaking. `-W source PROGRAM-TEXT' `--source PROGRAM-TEXT' Program source code is taken from the PROGRAM-TEXT. This option allows you to mix source code in files with source code that you enter on the command line. This is particularly useful when you have library functions that you wish to use from your command line programs (*note The `AWKPATH' Environment Variable: AWKPATH Variable.). `-W version' `--version' Prints version information for this particular copy of `gawk'. This allows you to determine if your copy of `gawk' is up to date with respect to whatever the Free Software Foundation is currently distributing. It is also useful for bug reports (*note Reporting Problems and Bugs: Bugs.). Any other options are flagged as invalid with a warning message, but are otherwise ignored. In compatibility mode, as a special case, if the value of FS supplied to the `-F' option is `t', then `FS' is set to the tab character (`"\t"'). This is only true for `--traditional', and not for `--posix' (*note Specifying How Fields are Separated: Field Separators.). The `-f' option may be used more than once on the command line. If it is, `awk' reads its program source from all of the named files, as if they had been concatenated together into one big file. This is useful for creating libraries of `awk' functions. Useful functions can be written once, and then retrieved from a standard place, instead of having to be included into each individual program. You can type in a program at the terminal and still use library functions, by specifying `-f /dev/tty'. `awk' will read a file from the terminal to use as part of the `awk' program. After typing your program, type `Control-d' (the end-of-file character) to terminate it. (You may also use `-f -' to read program source from the standard input, but then you will not be able to also use the standard input as a source of data.) Because it is clumsy using the standard `awk' mechanisms to mix source file and command line `awk' programs, `gawk' provides the `--source' option. This does not require you to pre-empt the standard input for your source code, and allows you to easily mix command line and library source code (*note The `AWKPATH' Environment Variable: AWKPATH Variable.). If no `-f' or `--source' option is specified, then `gawk' will use the first non-option command line argument as the text of the program source code. If the environment variable `POSIXLY_CORRECT' exists, then `gawk' will behave in strict POSIX mode, exactly as if you had supplied the `--posix' command line option. Many GNU programs look for this environment variable to turn on strict POSIX mode. If you supply `--lint' on the command line, and `gawk' turns on POSIX mode because of `POSIXLY_CORRECT', then it will print a warning message indicating that POSIX mode is in effect. You would typically set this variable in your shell's startup file. For a Bourne compatible shell (such as Bash), you would add these lines to the `.profile' file in your home directory. POSIXLY_CORRECT=true export POSIXLY_CORRECT For a `csh' compatible shell,(1) you would add this line to the `.login' file in your home directory. setenv POSIXLY_CORRECT true ---------- Footnotes ---------- (1) Not recommended.  File: gawk.info, Node: Other Arguments, Next: AWKPATH Variable, Prev: Options, Up: Invoking Gawk Other Command Line Arguments ============================ Any additional arguments on the command line are normally treated as input files to be processed in the order specified. However, an argument that has the form `VAR=VALUE', assigns the value VALUE to the variable VAR--it does not specify a file at all. All these arguments are made available to your `awk' program in the `ARGV' array (*note Built-in Variables::.). Command line options and the program text (if present) are omitted from `ARGV'. All other arguments, including variable assignments, are included. As each element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to the index in `ARGV' of the current element. The distinction between file name arguments and variable-assignment arguments is made when `awk' is about to open the next input file. At that point in execution, it checks the "file name" to see whether it is really a variable assignment; if so, `awk' sets the variable instead of reading a file. Therefore, the variables actually receive the given values after all previously specified files have been read. In particular, the values of variables assigned in this fashion are *not* available inside a `BEGIN' rule (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.), since such rules are run before `awk' begins scanning the argument list. The variable values given on the command line are processed for escape sequences (d.c.) (*note Escape Sequences::.). In some earlier implementations of `awk', when a variable assignment occurred before any file names, the assignment would happen *before* the `BEGIN' rule was executed. `awk''s behavior was thus inconsistent; some command line assignments were available inside the `BEGIN' rule, while others were not. However, some applications came to depend upon this "feature." When `awk' was changed to be more consistent, the `-v' option was added to accommodate applications that depended upon the old behavior. The variable assignment feature is most useful for assigning to variables such as `RS', `OFS', and `ORS', which control input and output formats, before scanning the data files. It is also useful for controlling state if multiple passes are needed over a data file. For example: awk 'pass == 1 { PASS 1 STUFF } pass == 2 { PASS 2 STUFF }' pass=1 mydata pass=2 mydata Given the variable assignment feature, the `-F' option for setting the value of `FS' is not strictly necessary. It remains for historical compatibility.  File: gawk.info, Node: AWKPATH Variable, Next: Obsolete, Prev: Other Arguments, Up: Invoking Gawk The `AWKPATH' Environment Variable ================================== The previous section described how `awk' program files can be named on the command line with the `-f' option. In most `awk' implementations, you must supply a precise path name for each program file, unless the file is in the current directory. But in `gawk', if the file name supplied to the `-f' option does not contain a `/', then `gawk' searches a list of directories (called the "search path"), one by one, looking for a file with the specified name. The search path is a string consisting of directory names separated by colons. `gawk' gets its search path from the `AWKPATH' environment variable. If that variable does not exist, `gawk' uses a default path, which is `.:/usr/local/share/awk'.(1) (Programs written for use by system administrators should use an `AWKPATH' variable that does not include the current directory, `.'.) The search path feature is particularly useful for building up libraries of useful `awk' functions. The library files can be placed in a standard directory that is in the default path, and then specified on the command line with a short file name. Otherwise, the full file name would have to be typed for each file. By using both the `--source' and `-f' options, your command line `awk' programs can use facilities in `awk' library files. *Note A Library of `awk' Functions: Library Functions. Path searching is not done if `gawk' is in compatibility mode. This is true for both `--traditional' and `--posix'. *Note Command Line Options: Options. *Note:* if you want files in the current directory to be found, you must include the current directory in the path, either by including `.' explicitly in the path, or by writing a null entry in the path. (A null entry is indicated by starting or ending the path with a colon, or by placing two colons next to each other (`::').) If the current directory is not included in the path, then files cannot be found in the current directory. This path search mechanism is identical to the shell's. Starting with version 3.0, if `AWKPATH' is not defined in the environment, `gawk' will place its default search path into `ENVIRON["AWKPATH"]'. This makes it easy to determine the actual search path `gawk' will use. ---------- Footnotes ---------- (1) Your version of `gawk' may use a directory that is different than `/usr/local/share/awk'; it will depend upon how `gawk' was built and installed. The actual directory will be the value of `$(datadir)' generated when `gawk' was configured. You probably don't need to worry about this though.  File: gawk.info, Node: Obsolete, Next: Undocumented, Prev: AWKPATH Variable, Up: Invoking Gawk Obsolete Options and/or Features ================================ This section describes features and/or command line options from previous releases of `gawk' that are either not available in the current version, or that are still supported but deprecated (meaning that they will *not* be in the next release). For version 3.0.3 of `gawk', there are no command line options or other deprecated features from the previous version of `gawk'. This node is thus essentially a place holder, in case some option becomes obsolete in a future version of `gawk'.  File: gawk.info, Node: Undocumented, Next: Known Bugs, Prev: Obsolete, Up: Invoking Gawk Undocumented Options and Features ================================= Use the Source, Luke! Obi-Wan This section intentionally left blank.  File: gawk.info, Node: Known Bugs, Prev: Undocumented, Up: Invoking Gawk Known Bugs in `gawk' ==================== * The `-F' option for changing the value of `FS' (*note Command Line Options: Options.) is not necessary given the command line variable assignment feature; it remains only for backwards compatibility. * If your system actually has support for `/dev/fd' and the associated `/dev/stdin', `/dev/stdout', and `/dev/stderr' files, you may get different output from `gawk' than you would get on a system without those files. When `gawk' interprets these files internally, it synchronizes output to the standard output with output to `/dev/stdout', while on a system with those files, the output is actually to different open files (*note Special File Names in `gawk': Special Files.). * Syntactically invalid single character programs tend to overflow the parse stack, generating a rather unhelpful message. Such programs are surprisingly difficult to diagnose in the completely general case, and the effort to do so really is not worth it.  File: gawk.info, Node: Library Functions, Next: Sample Programs, Prev: Invoking Gawk, Up: Top A Library of `awk' Functions **************************** This chapter presents a library of useful `awk' functions. The sample programs presented later (*note Practical `awk' Programs: Sample Programs.) use these functions. The functions are presented here in a progression from simple to complex. *Note Extracting Programs from Texinfo Source Files: Extract Program, presents a program that you can use to extract the source code for these example library functions and programs from the Texinfo source for this Info file. (This has already been done as part of the `gawk' distribution.) If you have written one or more useful, general purpose `awk' functions, and would like to contribute them for a subsequent edition of this Info file, please contact the author. *Note Reporting Problems and Bugs: Bugs, for information on doing this. Don't just send code, as you will be required to either place your code in the public domain, publish it under the GPL (*note GNU GENERAL PUBLIC LICENSE: Copying.), or assign the copyright in it to the Free Software Foundation. * Menu: * Portability Notes:: What to do if you don't have `gawk'. * Nextfile Function:: Two implementations of a `nextfile' function. * Assert Function:: A function for assertions in `awk' programs. * Round Function:: A function for rounding if `sprintf' does not do it correctly. * Ordinal Functions:: Functions for using characters as numbers and vice versa. * Join Function:: A function to join an array into a string. * Mktime Function:: A function to turn a date into a timestamp. * Gettimeofday Function:: A function to get formatted times. * Filetrans Function:: A function for handling data file transitions. * Getopt Function:: A function for processing command line arguments. * Passwd Functions:: Functions for getting user information. * Group Functions:: Functions for getting group information. * Library Names:: How to best name private global variables in library functions.  File: gawk.info, Node: Portability Notes, Next: Nextfile Function, Prev: Library Functions, Up: Library Functions Simulating `gawk'-specific Features =================================== The programs in this chapter and in *Note Practical `awk' Programs: Sample Programs, freely use features that are specific to `gawk'. This section briefly discusses how you can rewrite these programs for different implementations of `awk'. Diagnostic error messages are sent to `/dev/stderr'. Use `| "cat 1>&2"' instead of `> "/dev/stderr"', if your system does not have a `/dev/stderr', or if you cannot use `gawk'. A number of programs use `nextfile' (*note The `nextfile' Statement: Nextfile Statement.), to skip any remaining input in the input file. *Note Implementing `nextfile' as a Function: Nextfile Function, shows you how to write a function that will do the same thing. Finally, some of the programs choose to ignore upper-case and lower-case distinctions in their input. They do this by assigning one to `IGNORECASE'. You can achieve the same effect by adding the following rule to the beginning of the program: # ignore case { $0 = tolower($0) } Also, verify that all regexp and string constants used in comparisons only use lower-case letters.  File: gawk.info, Node: Nextfile Function, Next: Assert Function, Prev: Portability Notes, Up: Library Functions Implementing `nextfile' as a Function ===================================== The `nextfile' statement presented in *Note The `nextfile' Statement: Nextfile Statement, is a `gawk'-specific extension. It is not available in other implementations of `awk'. This section shows two versions of a `nextfile' function that you can use to simulate `gawk''s `nextfile' statement if you cannot use `gawk'. Here is a first attempt at writing a `nextfile' function. # nextfile --- skip remaining records in current file # this should be read in before the "main" awk program function nextfile() { _abandon_ = FILENAME; next } _abandon_ == FILENAME { next } This file should be included before the main program, because it supplies a rule that must be executed first. This rule compares the current data file's name (which is always in the `FILENAME' variable) to a private variable named `_abandon_'. If the file name matches, then the action part of the rule executes a `next' statement, to go on to the next record. (The use of `_' in the variable name is a convention. It is discussed more fully in *Note Naming Library Function Global Variables: Library Names.) The use of the `next' statement effectively creates a loop that reads all the records from the current data file. Eventually, the end of the file is reached, and a new data file is opened, changing the value of `FILENAME'. Once this happens, the comparison of `_abandon_' to `FILENAME' fails, and execution continues with the first rule of the "real" program. The `nextfile' function itself simply sets the value of `_abandon_' and then executes a `next' statement to start the loop going.(1) This initial version has a subtle problem. What happens if the same data file is listed *twice* on the command line, one right after the other, or even with just a variable assignment between the two occurrences of the file name? In such a case, this code will skip right through the file, a second time, even though it should stop when it gets to the end of the first occurrence. Here is a second version of `nextfile' that remedies this problem. # nextfile --- skip remaining records in current file # correctly handle successive occurrences of the same file # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May, 1993 # this should be read in before the "main" awk program function nextfile() { _abandon_ = FILENAME; next } _abandon_ == FILENAME { if (FNR == 1) _abandon_ = "" else next } The `nextfile' function has not changed. It sets `_abandon_' equal to the current file name and then executes a `next' satement. The `next' statement reads the next record and increments `FNR', so `FNR' is guaranteed to have a value of at least two. However, if `nextfile' is called for the last record in the file, then `awk' will close the current data file and move on to the next one. Upon doing so, `FILENAME' will be set to the name of the new file, and `FNR' will be reset to one. If this next file is the same as the previous one, `_abandon_' will still be equal to `FILENAME'. However, `FNR' will be equal to one, telling us that this is a new occurrence of the file, and not the one we were reading when the `nextfile' function was executed. In that case, `_abandon_' is reset to the empty string, so that further executions of this rule will fail (until the next time that `nextfile' is called). If `FNR' is not one, then we are still in the original data file, and the program executes a `next' statement to skip through it. An important question to ask at this point is: "Given that the functionality of `nextfile' can be provided with a library file, why is it built into `gawk'?" This is an important question. Adding features for little reason leads to larger, slower programs that are harder to maintain. The answer is that building `nextfile' into `gawk' provides significant gains in efficiency. If the `nextfile' function is executed at the beginning of a large data file, `awk' still has to scan the entire file, splitting it up into records, just to skip over it. The built-in `nextfile' can simply close the file immediately and proceed to the next one, saving a lot of time. This is particularly important in `awk', since `awk' programs are generally I/O bound (i.e. they spend most of their time doing input and output, instead of performing computations). ---------- Footnotes ---------- (1) Some implementations of `awk' do not allow you to execute `next' from within a function body. Some other work-around will be necessary if you use such a version.  File: gawk.info, Node: Assert Function, Next: Round Function, Prev: Nextfile Function, Up: Library Functions Assertions ========== When writing large programs, it is often useful to be able to know that a condition or set of conditions is true. Before proceeding with a particular computation, you make a statement about what you believe to be the case. Such a statement is known as an "assertion." The C language provides an `' header file and corresponding `assert' macro that the programmer can use to make assertions. If an assertion fails, the `assert' macro arranges to print a diagnostic message describing the condition that should have been true but was not, and then it kills the program. In C, using `assert' looks this: #include int myfunc(int a, double b) { assert(a <= 5 && b >= 17); ... } If the assertion failed, the program would print a message similar to this: prog.c:5: assertion failed: a <= 5 && b >= 17 The ANSI C language makes it possible to turn the condition into a string for use in printing the diagnostic message. This is not possible in `awk', so this `assert' function also requires a string version of the condition that is being tested. # assert --- assert that a condition is true. Otherwise exit. # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May, 1993 function assert(condition, string) { if (! condition) { printf("%s:%d: assertion failed: %s\n", FILENAME, FNR, string) > "/dev/stderr" _assert_exit = 1 exit 1 } } END { if (_assert_exit) exit 1 } The `assert' function tests the `condition' parameter. If it is false, it prints a message to standard error, using the `string' parameter to describe the failed condition. It then sets the variable `_assert_exit' to one, and executes the `exit' statement. The `exit' statement jumps to the `END' rule. If the `END' rules finds `_assert_exit' to be true, then it exits immediately. The purpose of the `END' rule with its test is to keep any other `END' rules from running. When an assertion fails, the program should exit immediately. If no assertions fail, then `_assert_exit' will still be false when the `END' rule is run normally, and the rest of the program's `END' rules will execute. For all of this to work correctly, `assert.awk' must be the first source file read by `awk'. You would use this function in your programs this way: function myfunc(a, b) { assert(a <= 5 && b >= 17, "a <= 5 && b >= 17") ... } If the assertion failed, you would see a message like this: mydata:1357: assertion failed: a <= 5 && b >= 17 There is a problem with this version of `assert', that it may not be possible to work around. An `END' rule is automatically added to the program calling `assert'. Normally, if a program consists of just a `BEGIN' rule, the input files and/or standard input are not read. However, now that the program has an `END' rule, `awk' will attempt to read the input data files, or standard input (*note Startup and Cleanup Actions: Using BEGIN/END.), most likely causing the program to hang, waiting for input.  File: gawk.info, Node: Round Function, Next: Ordinal Functions, Prev: Assert Function, Up: Library Functions Rounding Numbers ================ The way `printf' and `sprintf' (*note Using `printf' Statements for Fancier Printing: Printf.) do rounding will often depend upon the system's C `sprintf' subroutine. On many machines, `sprintf' rounding is "unbiased," which means it doesn't always round a trailing `.5' up, contrary to naive expectations. In unbiased rounding, `.5' rounds to even, rather than always up, so 1.5 rounds to 2 but 4.5 rounds to 4. The result is that if you are using a format that does rounding (e.g., `"%.0f"') you should check what your system does. The following function does traditional rounding; it might be useful if your awk's `printf' does unbiased rounding. # round --- do normal rounding # # Arnold Robbins, arnold@@gnu.ai.mit.edu, August, 1996 # Public Domain function round(x, ival, aval, fraction) { ival = int(x) # integer part, int() truncates # see if fractional part if (ival == x) # no fraction return x if (x < 0) { aval = -x # absolute value ival = int(aval) fraction = aval - ival if (fraction >= .5) return int(x) - 1 # -2.5 --> -3 else return int(x) # -2.3 --> -2 } else { fraction = x - ival if (fraction >= .5) return ival + 1 else return ival } } # test harness { print $0, round($0) }  File: gawk.info, Node: Ordinal Functions, Next: Join Function, Prev: Round Function, Up: Library Functions Translating Between Characters and Numbers ========================================== One commercial implementation of `awk' supplies a built-in function, `ord', which takes a character and returns the numeric value for that character in the machine's character set. If the string passed to `ord' has more than one character, only the first one is used. The inverse of this function is `chr' (from the function of the same name in Pascal), which takes a number and returns the corresponding character. Both functions can be written very nicely in `awk'; there is no real reason to build them into the `awk' interpreter. # ord.awk --- do ord and chr # # Global identifiers: # _ord_: numerical values indexed by characters # _ord_init: function to initialize _ord_ # # Arnold Robbins # arnold@@gnu.ai.mit.edu # Public Domain # 16 January, 1992 # 20 July, 1992, revised BEGIN { _ord_init() } function _ord_init( low, high, i, t) { low = sprintf("%c", 7) # BEL is ascii 7 if (low == "\a") { # regular ascii low = 0 high = 127 } else if (sprintf("%c", 128 + 7) == "\a") { # ascii, mark parity low = 128 high = 255 } else { # ebcdic(!) low = 0 high = 255 } for (i = low; i <= high; i++) { t = sprintf("%c", i) _ord_[t] = i } } Some explanation of the numbers used by `chr' is worthwhile. The most prominent character set in use today is ASCII. Although an eight-bit byte can hold 256 distinct values (from zero to 255), ASCII only defines characters that use the values from zero to 127.(1) At least one computer manufacturer that we know of uses ASCII, but with mark parity, meaning that the leftmost bit in the byte is always one. What this means is that on those systems, characters have numeric values from 128 to 255. Finally, large mainframe systems use the EBCDIC character set, which uses all 256 values. While there are other character sets in use on some older systems, they are not really worth worrying about. function ord(str, c) { # only first character is of interest c = substr(str, 1, 1) return _ord_[c] } function chr(c) { # force c to be numeric by adding 0 return sprintf("%c", c + 0) } #### test code #### # BEGIN \ # { # for (;;) { # printf("enter a character: ") # if (getline var <= 0) # break # printf("ord(%s) = %d\n", var, ord(var)) # } # } An obvious improvement to these functions would be to move the code for the `_ord_init' function into the body of the `BEGIN' rule. It was written this way initially for ease of development. There is a "test program" in a `BEGIN' rule, for testing the function. It is commented out for production use. ---------- Footnotes ---------- (1) ASCII has been extended in many countries to use the values from 128 to 255 for country-specific characters. If your system uses these extensions, you can simplify `_ord_init' to simply loop from zero to 255.  File: gawk.info, Node: Join Function, Next: Mktime Function, Prev: Ordinal Functions, Up: Library Functions Merging an Array Into a String ============================== When doing string processing, it is often useful to be able to join all the strings in an array into one long string. The following function, `join', accomplishes this task. It is used later in several of the application programs (*note Practical `awk' Programs: Sample Programs.). Good function design is important; this function needs to be general, but it should also have a reasonable default behavior. It is called with an array and the beginning and ending indices of the elements in the array to be merged. This assumes that the array indices are numeric--a reasonable assumption since the array was likely created with `split' (*note Built-in Functions for String Manipulation: String Functions.). # join.awk --- join an array into a string # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 function join(array, start, end, sep, result, i) { if (sep == "") sep = " " else if (sep == SUBSEP) # magic value sep = "" result = array[start] for (i = start + 1; i <= end; i++) result = result sep array[i] return result } An optional additional argument is the separator to use when joining the strings back together. If the caller supplies a non-empty value, `join' uses it. If it is not supplied, it will have a null value. In this case, `join' uses a single blank as a default separator for the strings. If the value is equal to `SUBSEP', then `join' joins the strings with no separator between them. `SUBSEP' serves as a "magic" value to indicate that there should be no separation between the component strings. It would be nice if `awk' had an assignment operator for concatenation. The lack of an explicit operator for concatenation makes string operations more difficult than they really need to be.  File: gawk.info, Node: Mktime Function, Next: Gettimeofday Function, Prev: Join Function, Up: Library Functions Turning Dates Into Timestamps ============================= The `systime' function built in to `gawk' returns the current time of day as a timestamp in "seconds since the Epoch." This timestamp can be converted into a printable date of almost infinitely variable format using the built-in `strftime' function. (For more information on `systime' and `strftime', *note Functions for Dealing with Time Stamps: Time Functions..) An interesting but difficult problem is to convert a readable representation of a date back into a timestamp. The ANSI C library provides a `mktime' function that does the basic job, converting a canonical representation of a date into a timestamp. It would appear at first glance that `gawk' would have to supply a `mktime' built-in function that was simply a "hook" to the C language version. In fact though, `mktime' can be implemented entirely in `awk'. Here is a version of `mktime' for `awk'. It takes a simple representation of the date and time, and converts it into a timestamp. The code is presented here intermixed with explanatory prose. In *Note Extracting Programs from Texinfo Source Files: Extract Program, you will see how the Texinfo source file for this Info file can be processed to extract the code into a single source file. The program begins with a descriptive comment and a `BEGIN' rule that initializes a table `_tm_months'. This table is a two-dimensional array that has the lengths of the months. The first index is zero for regular years, and one for leap years. The values are the same for all the months in both kinds of years, except for February; thus the use of multiple assignment. # mktime.awk --- convert a canonical date representation # into a timestamp # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 BEGIN \ { # Initialize table of month lengths _tm_months[0,1] = _tm_months[1,1] = 31 _tm_months[0,2] = 28; _tm_months[1,2] = 29 _tm_months[0,3] = _tm_months[1,3] = 31 _tm_months[0,4] = _tm_months[1,4] = 30 _tm_months[0,5] = _tm_months[1,5] = 31 _tm_months[0,6] = _tm_months[1,6] = 30 _tm_months[0,7] = _tm_months[1,7] = 31 _tm_months[0,8] = _tm_months[1,8] = 31 _tm_months[0,9] = _tm_months[1,9] = 30 _tm_months[0,10] = _tm_months[1,10] = 31 _tm_months[0,11] = _tm_months[1,11] = 30 _tm_months[0,12] = _tm_months[1,12] = 31 } The benefit of merging multiple `BEGIN' rules (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.) is particularly clear when writing library files. Functions in library files can cleanly initialize their own private data and also provide clean-up actions in private `END' rules. The next function is a simple one that computes whether a given year is or is not a leap year. If a year is evenly divisible by four, but not evenly divisible by 100, or if it is evenly divisible by 400, then it is a leap year. Thus, 1904 was a leap year, 1900 was not, but 2000 will be. # decide if a year is a leap year function _tm_isleap(year, ret) { ret = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0) return ret } This function is only used a few times in this file, and its computation could have been written "in-line" (at the point where it's used). Making it a separate function made the original development easier, and also avoids the possibility of typing errors when duplicating the code in multiple places. The next function is more interesting. It does most of the work of generating a timestamp, which is converting a date and time into some number of seconds since the Epoch. The caller passes an array (rather imaginatively named `a') containing six values: the year including century, the month as a number between one and 12, the day of the month, the hour as a number between zero and 23, the minute in the hour, and the seconds within the minute. The function uses several local variables to precompute the number of seconds in an hour, seconds in a day, and seconds in a year. Often, similar C code simply writes out the expression in-line, expecting the compiler to do "constant folding". E.g., most C compilers would turn `60 * 60' into `3600' at compile time, instead of recomputing it every time at run time. Precomputing these values makes the function more efficient. # convert a date into seconds function _tm_addup(a, total, yearsecs, daysecs, hoursecs, i, j) { hoursecs = 60 * 60 daysecs = 24 * hoursecs yearsecs = 365 * daysecs total = (a[1] - 1970) * yearsecs # extra day for leap years for (i = 1970; i < a[1]; i++) if (_tm_isleap(i)) total += daysecs j = _tm_isleap(a[1]) for (i = 1; i < a[2]; i++) total += _tm_months[j, i] * daysecs total += (a[3] - 1) * daysecs total += a[4] * hoursecs total += a[5] * 60 total += a[6] return total } The function starts with a first approximation of all the seconds between Midnight, January 1, 1970,(1) and the beginning of the current year. It then goes through all those years, and for every leap year, adds an additional day's worth of seconds. The variable `j' holds either one or zero, if the current year is or is not a leap year. For every month in the current year prior to the current month, it adds the number of seconds in the month, using the appropriate entry in the `_tm_months' array. Finally, it adds in the seconds for the number of days prior to the current day, and the number of hours, minutes, and seconds in the current day. The result is a count of seconds since January 1, 1970. This value is not yet what is needed though. The reason why is described shortly. The main `mktime' function takes a single character string argument. This string is a representation of a date and time in a "canonical" (fixed) form. This string should be `"YEAR MONTH DAY HOUR MINUTE SECOND"'. # mktime --- convert a date into seconds, # compensate for time zone function mktime(str, res1, res2, a, b, i, j, t, diff) { i = split(str, a, " ") # don't rely on FS if (i != 6) return -1 # force numeric for (j in a) a[j] += 0 # validate if (a[1] < 1970 || a[2] < 1 || a[2] > 12 || a[3] < 1 || a[3] > 31 || a[4] < 0 || a[4] > 23 || a[5] < 0 || a[5] > 59 || a[6] < 0 || a[6] > 60 ) return -1 res1 = _tm_addup(a) t = strftime("%Y %m %d %H %M %S", res1) if (_tm_debug) printf("(%s) -> (%s)\n", str, t) > "/dev/stderr" split(t, b, " ") res2 = _tm_addup(b) diff = res1 - res2 if (_tm_debug) printf("diff = %d seconds\n", diff) > "/dev/stderr" res1 += diff return res1 } The function first splits the string into an array, using spaces and tabs as separators. If there are not six elements in the array, it returns an error, signaled as the value -1. Next, it forces each element of the array to be numeric, by adding zero to it. The following `if' statement then makes sure that each element is within an allowable range. (This checking could be extended further, e.g., to make sure that the day of the month is within the correct range for the particular month supplied.) All of this is essentially preliminary set-up and error checking. Recall that `_tm_addup' generated a value in seconds since Midnight, January 1, 1970. This value is not directly usable as the result we want, *since the calculation does not account for the local timezone*. In other words, the value represents the count in seconds since the Epoch, but only for UTC (Universal Coordinated Time). If the local timezone is east or west of UTC, then some number of hours should be either added to, or subtracted from the resulting timestamp. For example, 6:23 p.m. in Atlanta, Georgia (USA), is normally five hours west of (behind) UTC. It is only four hours behind UTC if daylight savings time is in effect. If you are calling `mktime' in Atlanta, with the argument `"1993 5 23 18 23 12"', the result from `_tm_addup' will be for 6:23 p.m. UTC, which is only 2:23 p.m. in Atlanta. It is necessary to add another four hours worth of seconds to the result. How can `mktime' determine how far away it is from UTC? This is surprisingly easy. The returned timestamp represents the time passed to `mktime' *as UTC*. This timestamp can be fed back to `strftime', which will format it as a *local* time; i.e. as if it already had the UTC difference added in to it. This is done by giving `"%Y %m %d %H %M %S"' to `strftime' as the format argument. It returns the computed timestamp in the original string format. The result represents a time that accounts for the UTC difference. When the new time is converted back to a timestamp, the difference between the two timestamps is the difference (in seconds) between the local timezone and UTC. This difference is then added back to the original result. An example demonstrating this is presented below. Finally, there is a "main" program for testing the function. BEGIN { if (_tm_test) { printf "Enter date as yyyy mm dd hh mm ss: " getline _tm_test_date t = mktime(_tm_test_date) r = strftime("%Y %m %d %H %M %S", t) printf "Got back (%s)\n", r } } The entire program uses two variables that can be set on the command line to control debugging output and to enable the test in the final `BEGIN' rule. Here is the result of a test run. (Note that debugging output is to standard error, and test output is to standard output.) $ gawk -f mktime.awk -v _tm_test=1 -v _tm_debug=1 -| Enter date as yyyy mm dd hh mm ss: 1993 5 23 15 35 10 error--> (1993 5 23 15 35 10) -> (1993 05 23 11 35 10) error--> diff = 14400 seconds -| Got back (1993 05 23 15 35 10) The time entered was 3:35 p.m. (15:35 on a 24-hour clock), on May 23, 1993. The first line of debugging output shows the resulting time as UTC--four hours ahead of the local time zone. The second line shows that the difference is 14400 seconds, which is four hours. (The difference is only four hours, since daylight savings time is in effect during May.) The final line of test output shows that the timezone compensation algorithm works; the returned time is the same as the entered time. This program does not solve the general problem of turning an arbitrary date representation into a timestamp. That problem is very involved. However, the `mktime' function provides a foundation upon which to build. Other software can convert month names into numeric months, and AM/PM times into 24-hour clocks, to generate the "canonical" format that `mktime' requires. ---------- Footnotes ---------- (1) This is the Epoch on POSIX systems. It may be different on other systems.  File: gawk.info, Node: Gettimeofday Function, Next: Filetrans Function, Prev: Mktime Function, Up: Library Functions Managing the Time of Day ======================== The `systime' and `strftime' functions described in *Note Functions for Dealing with Time Stamps: Time Functions, provide the minimum functionality necessary for dealing with the time of day in human readable form. While `strftime' is extensive, the control formats are not necessarily easy to remember or intuitively obvious when reading a program. The following function, `gettimeofday', populates a user-supplied array with pre-formatted time information. It returns a string with the current time formatted in the same way as the `date' utility. # gettimeofday --- get the time of day in a usable format # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain, May 1993 # # Returns a string in the format of output of date(1) # Populates the array argument time with individual values: # time["second"] -- seconds (0 - 59) # time["minute"] -- minutes (0 - 59) # time["hour"] -- hours (0 - 23) # time["althour"] -- hours (0 - 12) # time["monthday"] -- day of month (1 - 31) # time["month"] -- month of year (1 - 12) # time["monthname"] -- name of the month # time["shortmonth"] -- short name of the month # time["year"] -- year within century (0 - 99) # time["fullyear"] -- year with century (19xx or 20xx) # time["weekday"] -- day of week (Sunday = 0) # time["altweekday"] -- day of week (Monday = 0) # time["weeknum"] -- week number, Sunday first day # time["altweeknum"] -- week number, Monday first day # time["dayname"] -- name of weekday # time["shortdayname"] -- short name of weekday # time["yearday"] -- day of year (0 - 365) # time["timezone"] -- abbreviation of timezone name # time["ampm"] -- AM or PM designation function gettimeofday(time, ret, now, i) { # get time once, avoids unnecessary system calls now = systime() # return date(1)-style output ret = strftime("%a %b %d %H:%M:%S %Z %Y", now) # clear out target array for (i in time) delete time[i] # fill in values, force numeric values to be # numeric by adding 0 time["second"] = strftime("%S", now) + 0 time["minute"] = strftime("%M", now) + 0 time["hour"] = strftime("%H", now) + 0 time["althour"] = strftime("%I", now) + 0 time["monthday"] = strftime("%d", now) + 0 time["month"] = strftime("%m", now) + 0 time["monthname"] = strftime("%B", now) time["shortmonth"] = strftime("%b", now) time["year"] = strftime("%y", now) + 0 time["fullyear"] = strftime("%Y", now) + 0 time["weekday"] = strftime("%w", now) + 0 time["altweekday"] = strftime("%u", now) + 0 time["dayname"] = strftime("%A", now) time["shortdayname"] = strftime("%a", now) time["yearday"] = strftime("%j", now) + 0 time["timezone"] = strftime("%Z", now) time["ampm"] = strftime("%p", now) time["weeknum"] = strftime("%U", now) + 0 time["altweeknum"] = strftime("%W", now) + 0 return ret } The string indices are easier to use and read than the various formats required by `strftime'. The `alarm' program presented in *Note An Alarm Clock Program: Alarm Program, uses this function. The `gettimeofday' function is presented above as it was written. A more general design for this function would have allowed the user to supply an optional timestamp value that would have been used instead of the current time.  File: gawk.info, Node: Filetrans Function, Next: Getopt Function, Prev: Gettimeofday Function, Up: Library Functions Noting Data File Boundaries =========================== The `BEGIN' and `END' rules are each executed exactly once, at the beginning and end respectively of your `awk' program (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). We (the `gawk' authors) once had a user who mistakenly thought that the `BEGIN' rule was executed at the beginning of each data file and the `END' rule was executed at the end of each data file. When informed that this was not the case, the user requested that we add new special patterns to `gawk', named `BEGIN_FILE' and `END_FILE', that would have the desired behavior. He even supplied us the code to do so. However, after a little thought, I came up with the following library program. It arranges to call two user-supplied functions, `beginfile' and `endfile', at the beginning and end of each data file. Besides solving the problem in only nine(!) lines of code, it does so *portably*; this will work with any implementation of `awk'. # transfile.awk # # Give the user a hook for filename transitions # # The user must supply functions beginfile() and endfile() # that each take the name of the file being started or # finished, respectively. # # Arnold Robbins, arnold@@gnu.ai.mit.edu, January 1992 # Public Domain FILENAME != _oldfilename \ { if (_oldfilename != "") endfile(_oldfilename) _oldfilename = FILENAME beginfile(FILENAME) } END { endfile(FILENAME) } This file must be loaded before the user's "main" program, so that the rule it supplies will be executed first. This rule relies on `awk''s `FILENAME' variable that automatically changes for each new data file. The current file name is saved in a private variable, `_oldfilename'. If `FILENAME' does not equal `_oldfilename', then a new data file is being processed, and it is necessary to call `endfile' for the old file. Since `endfile' should only be called if a file has been processed, the program first checks to make sure that `_oldfilename' is not the null string. The program then assigns the current file name to `_oldfilename', and calls `beginfile' for the file. Since, like all `awk' variables, `_oldfilename' will be initialized to the null string, this rule executes correctly even for the first data file. The program also supplies an `END' rule, to do the final processing for the last file. Since this `END' rule comes before any `END' rules supplied in the "main" program, `endfile' will be called first. Once again the value of multiple `BEGIN' and `END' rules should be clear. This version has same problem as the first version of `nextfile' (*note Implementing `nextfile' as a Function: Nextfile Function.). If the same data file occurs twice in a row on command line, then `endfile' and `beginfile' will not be executed at the end of the first pass and at the beginning of the second pass. This version solves the problem. # ftrans.awk --- handle data file transitions # # user supplies beginfile() and endfile() functions # # Arnold Robbins, arnold@@gnu.ai.mit.edu. November 1992 # Public Domain FNR == 1 { if (_filename_ != "") endfile(_filename_) _filename_ = FILENAME beginfile(FILENAME) } END { endfile(_filename_) } In *Note Counting Things: Wc Program, you will see how this library function can be used, and how it simplifies writing the main program.  File: gawk.info, Node: Getopt Function, Next: Passwd Functions, Prev: Filetrans Function, Up: Library Functions Processing Command Line Options =============================== Most utilities on POSIX compatible systems take options or "switches" on the command line that can be used to change the way a program behaves. `awk' is an example of such a program (*note Command Line Options: Options.). Often, options take "arguments", data that the program needs to correctly obey the command line option. For example, `awk''s `-F' option requires a string to use as the field separator. The first occurrence on the command line of either `--' or a string that does not begin with `-' ends the options. Most Unix systems provide a C function named `getopt' for processing command line arguments. The programmer provides a string describing the one letter options. If an option requires an argument, it is followed in the string with a colon. `getopt' is also passed the count and values of the command line arguments, and is called in a loop. `getopt' processes the command line arguments for option letters. Each time around the loop, it returns a single character representing the next option letter that it found, or `?' if it found an invalid option. When it returns -1, there are no options left on the command line. When using `getopt', options that do not take arguments can be grouped together. Furthermore, options that take arguments require that the argument be present. The argument can immediately follow the option letter, or it can be a separate command line argument. Given a hypothetical program that takes three command line options, `-a', `-b', and `-c', and `-b' requires an argument, all of the following are valid ways of invoking the program: prog -a -b foo -c data1 data2 data3 prog -ac -bfoo -- data1 data2 data3 prog -acbfoo data1 data2 data3 Notice that when the argument is grouped with its option, the rest of the command line argument is considered to be the option's argument. In the above example, `-acbfoo' indicates that all of the `-a', `-b', and `-c' options were supplied, and that `foo' is the argument to the `-b' option. `getopt' provides four external variables that the programmer can use. `optind' The index in the argument value array (`argv') where the first non-option command line argument can be found. `optarg' The string value of the argument to an option. `opterr' Usually `getopt' prints an error message when it finds an invalid option. Setting `opterr' to zero disables this feature. (An application might wish to print its own error message.) `optopt' The letter representing the command line option. While not usually documented, most versions supply this variable. The following C fragment shows how `getopt' might process command line arguments for `awk'. int main(int argc, char *argv[]) { ... /* print our own message */ opterr = 0; while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) { switch (c) { case 'f': /* file */ ... break; case 'F': /* field separator */ ... break; case 'v': /* variable assignment */ ... break; case 'W': /* extension */ ... break; case '?': default: usage(); break; } } ... } As a side point, `gawk' actually uses the GNU `getopt_long' function to process both normal and GNU-style long options (*note Command Line Options: Options.). The abstraction provided by `getopt' is very useful, and would be quite handy in `awk' programs as well. Here is an `awk' version of `getopt'. This function highlights one of the greatest weaknesses in `awk', which is that it is very poor at manipulating single characters. Repeated calls to `substr' are necessary for accessing individual characters (*note Built-in Functions for String Manipulation: String Functions.). The discussion walks through the code a bit at a time. # getopt --- do C library getopt(3) function in awk # # arnold@@gnu.ai.mit.edu # Public domain # # Initial version: March, 1991 # Revised: May, 1993 # External variables: # Optind -- index of ARGV for first non-option argument # Optarg -- string value of argument to current option # Opterr -- if non-zero, print our own diagnostic # Optopt -- current option letter # Returns # -1 at end of options # ? for unrecognized option # a character representing the current option # Private Data # _opti index in multi-flag option, e.g., -abc The function starts out with some documentation: who wrote the code, and when it was revised, followed by a list of the global variables it uses, what the return values are and what they mean, and any global variables that are "private" to this library function. Such documentation is essential for any program, and particularly for library functions. function getopt(argc, argv, options, optl, thisopt, i) { optl = length(options) if (optl == 0) # no options given return -1 if (argv[Optind] == "--") { # all done Optind++ _opti = 0 return -1 } else if (argv[Optind] !~ /^-[^: \t\n\f\r\v\b]/) { _opti = 0 return -1 } The function first checks that it was indeed called with a string of options (the `options' parameter). If `options' has a zero length, `getopt' immediately returns -1. The next thing to check for is the end of the options. A `--' ends the command line options, as does any command line argument that does not begin with a `-'. `Optind' is used to step through the array of command line arguments; it retains its value across calls to `getopt', since it is a global variable. The regexp used, `/^-[^: \t\n\f\r\v\b]/', is perhaps a bit of overkill; it checks for a `-' followed by anything that is not whitespace and not a colon. If the current command line argument does not match this pattern, it is not an option, and it ends option processing. if (_opti == 0) _opti = 2 thisopt = substr(argv[Optind], _opti, 1) Optopt = thisopt i = index(options, thisopt) if (i == 0) { if (Opterr) printf("%c -- invalid option\n", thisopt) > "/dev/stderr" if (_opti >= length(argv[Optind])) { Optind++ _opti = 0 } else _opti++ return "?" } The `_opti' variable tracks the position in the current command line argument (`argv[Optind]'). In the case that multiple options were grouped together with one `-' (e.g., `-abx'), it is necessary to return them to the user one at a time. If `_opti' is equal to zero, it is set to two, the index in the string of the next character to look at (we skip the `-', which is at position one). The variable `thisopt' holds the character, obtained with `substr'. It is saved in `Optopt' for the main program to use. If `thisopt' is not in the `options' string, then it is an invalid option. If `Opterr' is non-zero, `getopt' prints an error message on the standard error that is similar to the message from the C version of `getopt'. Since the option is invalid, it is necessary to skip it and move on to the next option character. If `_opti' is greater than or equal to the length of the current command line argument, then it is necessary to move on to the next one, so `Optind' is incremented and `_opti' is reset to zero. Otherwise, `Optind' is left alone and `_opti' is merely incremented. In any case, since the option was invalid, `getopt' returns `?'. The main program can examine `Optopt' if it needs to know what the invalid option letter actually was. if (substr(options, i + 1, 1) == ":") { # get option argument if (length(substr(argv[Optind], _opti + 1)) > 0) Optarg = substr(argv[Optind], _opti + 1) else Optarg = argv[++Optind] _opti = 0 } else Optarg = "" If the option requires an argument, the option letter is followed by a colon in the `options' string. If there are remaining characters in the current command line argument (`argv[Optind]'), then the rest of that string is assigned to `Optarg'. Otherwise, the next command line argument is used (`-xFOO' vs. `-x FOO'). In either case, `_opti' is reset to zero, since there are no more characters left to examine in the current command line argument. if (_opti == 0 || _opti >= length(argv[Optind])) { Optind++ _opti = 0 } else _opti++ return thisopt } Finally, if `_opti' is either zero or greater than the length of the current command line argument, it means this element in `argv' is through being processed, so `Optind' is incremented to point to the next element in `argv'. If neither condition is true, then only `_opti' is incremented, so that the next option letter can be processed on the next call to `getopt'. BEGIN { Opterr = 1 # default is to diagnose Optind = 1 # skip ARGV[0] # test program if (_getopt_test) { while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1) printf("c = <%c>, optarg = <%s>\n", _go_c, Optarg) printf("non-option arguments:\n") for (; Optind < ARGC; Optind++) printf("\tARGV[%d] = <%s>\n", Optind, ARGV[Optind]) } } The `BEGIN' rule initializes both `Opterr' and `Optind' to one. `Opterr' is set to one, since the default behavior is for `getopt' to print a diagnostic message upon seeing an invalid option. `Optind' is set to one, since there's no reason to look at the program name, which is in `ARGV[0]'. The rest of the `BEGIN' rule is a simple test program. Here is the result of two sample runs of the test program. $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x -| c = , optarg = <> -| c = , optarg = <> -| c = , optarg = -| non-option arguments: -| ARGV[3] = -| ARGV[4] = <-x> $ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc -| c = , optarg = <> error--> x -- invalid option -| c = , optarg = <> -| non-option arguments: -| ARGV[4] = -| ARGV[5] = The first `--' terminates the arguments to `awk', so that it does not try to interpret the `-a' etc. as its own options. Several of the sample programs presented in *Note Practical `awk' Programs: Sample Programs, use `getopt' to process their arguments.  File: gawk.info, Node: Passwd Functions, Next: Group Functions, Prev: Getopt Function, Up: Library Functions Reading the User Database ========================= The `/dev/user' special file (*note Special File Names in `gawk': Special Files.) provides access to the current user's real and effective user and group id numbers, and if available, the user's supplementary group set. However, since these are numbers, they do not provide very useful information to the average user. There needs to be some way to find the user information associated with the user and group numbers. This section presents a suite of functions for retrieving information from the user database. *Note Reading the Group Database: Group Functions, for a similar suite that retrieves information from the group database. The POSIX standard does not define the file where user information is kept. Instead, it provides the `' header file and several C language subroutines for obtaining user information. The primary function is `getpwent', for "get password entry." The "password" comes from the original user database file, `/etc/passwd', which kept user information, along with the encrypted passwords (hence the name). While an `awk' program could simply read `/etc/passwd' directly (the format is well known), because of the way password files are handled on networked systems, this file may not contain complete information about the system's set of users. To be sure of being able to produce a readable, complete version of the user database, it is necessary to write a small C program that calls `getpwent'. `getpwent' is defined to return a pointer to a `struct passwd'. Each time it is called, it returns the next entry in the database. When there are no more entries, it returns `NULL', the null pointer. When this happens, the C program should call `endpwent' to close the database. Here is `pwcat', a C program that "cats" the password database. /* * pwcat.c * * Generate a printable version of the password database * * Arnold Robbins * arnold@@gnu.ai.mit.edu * May 1993 * Public Domain */ #include #include int main(argc, argv) int argc; char **argv; { struct passwd *p; while ((p = getpwent()) != NULL) printf("%s:%s:%d:%d:%s:%s:%s\n", p->pw_name, p->pw_passwd, p->pw_uid, p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell); endpwent(); exit(0); } If you don't understand C, don't worry about it. The output from `pwcat' is the user database, in the traditional `/etc/passwd' format of colon-separated fields. The fields are: Login name The user's login name. Encrypted password The user's encrypted password. This may not be available on some systems. User-ID The user's numeric user-id number. Group-ID The user's numeric group-id number. Full name The user's full name, and perhaps other information associated with the user. Home directory The user's login, or "home" directory (familiar to shell programmers as `$HOME'). Login shell The program that will be run when the user logs in. This is usually a shell, such as Bash (the Gnu Bourne-Again shell). Here are a few lines representative of `pwcat''s output. $ pwcat -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh -| nobody:*:65534:65534::/: -| daemon:*:1:1::/: -| sys:*:2:2::/:/bin/csh -| bin:*:3:3::/bin: -| arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh -| miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh -| andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh ... With that introduction, here is a group of functions for getting user information. There are several functions here, corresponding to the C functions of the same name. # passwd.awk --- access password file information # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 BEGIN { # tailor this to suit your system _pw_awklib = "/usr/local/libexec/awk/" } function _pw_init( oldfs, oldrs, olddol0, pwcat) { if (_pw_inited) return oldfs = FS oldrs = RS olddol0 = $0 FS = ":" RS = "\n" pwcat = _pw_awklib "pwcat" while ((pwcat | getline) > 0) { _pw_byname[$1] = $0 _pw_byuid[$3] = $0 _pw_bycount[++_pw_total] = $0 } close(pwcat) _pw_count = 0 _pw_inited = 1 FS = oldfs RS = oldrs $0 = olddol0 } The `BEGIN' rule sets a private variable to the directory where `pwcat' is stored. Since it is used to help out an `awk' library routine, we have chosen to put it in `/usr/local/libexec/awk'. You might want it to be in a different directory on your system. The function `_pw_init' keeps three copies of the user information in three associative arrays. The arrays are indexed by user name (`_pw_byname'), by user-id number (`_pw_byuid'), and by order of occurrence (`_pw_bycount'). The variable `_pw_inited' is used for efficiency; `_pw_init' only needs to be called once. Since this function uses `getline' to read information from `pwcat', it first saves the values of `FS', `RS', and `$0'. Doing so is necessary, since these functions could be called from anywhere within a user's program, and the user may have his or her own values for `FS' and `RS'. The main part of the function uses a loop to read database lines, split the line into fields, and then store the line into each array as necessary. When the loop is done, `_pw_init' cleans up by closing the pipeline, setting `_pw_inited' to one, and restoring `FS', `RS', and `$0'. The use of `_pw_count' will be explained below. function getpwnam(name) { _pw_init() if (name in _pw_byname) return _pw_byname[name] return "" } The `getpwnam' function takes a user name as a string argument. If that user is in the database, it returns the appropriate line. Otherwise it returns the null string. function getpwuid(uid) { _pw_init() if (uid in _pw_byuid) return _pw_byuid[uid] return "" } Similarly, the `getpwuid' function takes a user-id number argument. If that user number is in the database, it returns the appropriate line. Otherwise it returns the null string. function getpwent() { _pw_init() if (_pw_count < _pw_total) return _pw_bycount[++_pw_count] return "" } The `getpwent' function simply steps through the database, one entry at a time. It uses `_pw_count' to track its current position in the `_pw_bycount' array. function endpwent() { _pw_count = 0 } The `endpwent' function resets `_pw_count' to zero, so that subsequent calls to `getpwent' will start over again. A conscious design decision in this suite is that each subroutine calls `_pw_init' to initialize the database arrays. The overhead of running a separate process to generate the user database, and the I/O to scan it, will only be incurred if the user's main program actually calls one of these functions. If this library file is loaded along with a user's program, but none of the routines are ever called, then there is no extra run-time overhead. (The alternative would be to move the body of `_pw_init' into a `BEGIN' rule, which would always run `pwcat'. This simplifies the code but runs an extra process that may never be needed.) In turn, calling `_pw_init' is not too expensive, since the `_pw_inited' variable keeps the program from reading the data more than once. If you are worried about squeezing every last cycle out of your `awk' program, the check of `_pw_inited' could be moved out of `_pw_init' and duplicated in all the other functions. In practice, this is not necessary, since most `awk' programs are I/O bound, and it would clutter up the code. The `id' program in *Note Printing Out User Information: Id Program, uses these functions.  File: gawk.info, Node: Group Functions, Next: Library Names, Prev: Passwd Functions, Up: Library Functions Reading the Group Database ========================== Much of the discussion presented in *Note Reading the User Database: Passwd Functions, applies to the group database as well. Although there has traditionally been a well known file, `/etc/group', in a well known format, the POSIX standard only provides a set of C library routines (`' and `getgrent') for accessing the information. Even though this file may exist, it likely does not have complete information. Therefore, as with the user database, it is necessary to have a small C program that generates the group database as its output. Here is `grcat', a C program that "cats" the group database. /* * grcat.c * * Generate a printable version of the group database * * Arnold Robbins, arnold@@gnu.ai.mit.edu * May 1993 * Public Domain */ #include #include int main(argc, argv) int argc; char **argv; { struct group *g; int i; while ((g = getgrent()) != NULL) { printf("%s:%s:%d:", g->gr_name, g->gr_passwd, g->gr_gid); for (i = 0; g->gr_mem[i] != NULL; i++) { printf("%s", g->gr_mem[i]); if (g->gr_mem[i+1] != NULL) putchar(','); } putchar('\n'); } endgrent(); exit(0); } Each line in the group database represent one group. The fields are separated with colons, and represent the following information. Group Name The name of the group. Group Password The encrypted group password. In practice, this field is never used. It is usually empty, or set to `*'. Group ID Number The numeric group-id number. This number should be unique within the file. Group Member List A comma-separated list of user names. These users are members of the group. Most Unix systems allow users to be members of several groups simultaneously. If your system does, then reading `/dev/user' will return those group-id numbers in `$5' through `$NF'. (Note that `/dev/user' is a `gawk' extension; *note Special File Names in `gawk': Special Files..) Here is what running `grcat' might produce: $ grcat -| wheel:*:0:arnold -| nogroup:*:65534: -| daemon:*:1: -| kmem:*:2: -| staff:*:10:arnold,miriam,andy -| other:*:20: ... Here are the functions for obtaining information from the group database. There are several, modeled after the C library functions of the same names. # group.awk --- functions for dealing with the group file # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 BEGIN \ { # Change to suit your system _gr_awklib = "/usr/local/libexec/awk/" } function _gr_init( oldfs, oldrs, olddol0, grcat, n, a, i) { if (_gr_inited) return oldfs = FS oldrs = RS olddol0 = $0 FS = ":" RS = "\n" grcat = _gr_awklib "grcat" while ((grcat | getline) > 0) { if ($1 in _gr_byname) _gr_byname[$1] = _gr_byname[$1] "," $4 else _gr_byname[$1] = $0 if ($3 in _gr_bygid) _gr_bygid[$3] = _gr_bygid[$3] "," $4 else _gr_bygid[$3] = $0 n = split($4, a, "[ \t]*,[ \t]*") for (i = 1; i <= n; i++) if (a[i] in _gr_groupsbyuser) _gr_groupsbyuser[a[i]] = \ _gr_groupsbyuser[a[i]] " " $1 else _gr_groupsbyuser[a[i]] = $1 _gr_bycount[++_gr_count] = $0 } close(grcat) _gr_count = 0 _gr_inited++ FS = oldfs RS = oldrs $0 = olddol0 } The `BEGIN' rule sets a private variable to the directory where `grcat' is stored. Since it is used to help out an `awk' library routine, we have chosen to put it in `/usr/local/libexec/awk'. You might want it to be in a different directory on your system. These routines follow the same general outline as the user database routines (*note Reading the User Database: Passwd Functions.). The `_gr_inited' variable is used to ensure that the database is scanned no more than once. The `_gr_init' function first saves `FS', `RS', and `$0', and then sets `FS' and `RS' to the correct values for scanning the group information. The group information is stored is several associative arrays. The arrays are indexed by group name (`_gr_byname'), by group-id number (`_gr_bygid'), and by position in the database (`_gr_bycount'). There is an additional array indexed by user name (`_gr_groupsbyuser'), that is a space separated list of groups that each user belongs to. Unlike the user database, it is possible to have multiple records in the database for the same group. This is common when a group has a large number of members. Such a pair of entries might look like: tvpeople:*:101:johny,jay,arsenio tvpeople:*:101:david,conan,tom,joan For this reason, `_gr_init' looks to see if a group name or group-id number has already been seen. If it has, then the user names are simply concatenated onto the previous list of users. (There is actually a subtle problem with the code presented above. Suppose that the first time there were no names. This code adds the names with a leading comma. It also doesn't check that there is a `$4'.) Finally, `_gr_init' closes the pipeline to `grcat', restores `FS', `RS', and `$0', initializes `_gr_count' to zero (it is used later), and makes `_gr_inited' non-zero. function getgrnam(group) { _gr_init() if (group in _gr_byname) return _gr_byname[group] return "" } The `getgrnam' function takes a group name as its argument, and if that group exists, it is returned. Otherwise, `getgrnam' returns the null string. function getgrgid(gid) { _gr_init() if (gid in _gr_bygid) return _gr_bygid[gid] return "" } The `getgrgid' function is similar, it takes a numeric group-id, and looks up the information associated with that group-id. function getgruser(user) { _gr_init() if (user in _gr_groupsbyuser) return _gr_groupsbyuser[user] return "" } The `getgruser' function does not have a C counterpart. It takes a user name, and returns the list of groups that have the user as a member. function getgrent() { _gr_init() if (++gr_count in _gr_bycount) return _gr_bycount[_gr_count] return "" } The `getgrent' function steps through the database one entry at a time. It uses `_gr_count' to track its position in the list. function endgrent() { _gr_count = 0 } `endgrent' resets `_gr_count' to zero so that `getgrent' can start over again. As with the user database routines, each function calls `_gr_init' to initialize the arrays. Doing so only incurs the extra overhead of running `grcat' if these functions are used (as opposed to moving the body of `_gr_init' into a `BEGIN' rule). Most of the work is in scanning the database and building the various associative arrays. The functions that the user calls are themselves very simple, relying on `awk''s associative arrays to do work. The `id' program in *Note Printing Out User Information: Id Program, uses these functions.  File: gawk.info, Node: Library Names, Prev: Group Functions, Up: Library Functions Naming Library Function Global Variables ======================================== Due to the way the `awk' language evolved, variables are either "global" (usable by the entire program), or "local" (usable just by a specific function). There is no intermediate state analogous to `static' variables in C. Library functions often need to have global variables that they can use to preserve state information between calls to the function. For example, `getopt''s variable `_opti' (*note Processing Command Line Options: Getopt Function.), and the `_tm_months' array used by `mktime' (*note Turning Dates Into Timestamps: Mktime Function.). Such variables are called "private", since the only functions that need to use them are the ones in the library. When writing a library function, you should try to choose names for your private variables so that they will not conflict with any variables used by either another library function or a user's main program. For example, a name like `i' or `j' is not a good choice, since user programs often use variable names like these for their own purposes. The example programs shown in this chapter all start the names of their private variables with an underscore (`_'). Users generally don't use leading underscores in their variable names, so this convention immediately decreases the chances that the variable name will be accidentally shared with the user's program. In addition, several of the library functions use a prefix that helps indicate what function or set of functions uses the variables. For example, `_tm_months' in `mktime' (*note Turning Dates Into Timestamps: Mktime Function.), and `_pw_byname' in the user data base routines (*note Reading the User Database: Passwd Functions.). This convention is recommended, since it even further decreases the chance of inadvertent conflict among variable names. Note that this convention can be used equally well both for variable names and for private function names too. While I could have re-written all the library routines to use this convention, I did not do so, in order to show how my own `awk' programming style has evolved, and to provide some basis for this discussion. As a final note on variable naming, if a function makes global variables available for use by a main program, it is a good convention to start that variable's name with a capital letter. For example, `getopt''s `Opterr' and `Optind' variables (*note Processing Command Line Options: Getopt Function.). The leading capital letter indicates that it is global, while the fact that the variable name is not all capital letters indicates that the variable is not one of `awk''s built-in variables, like `FS'. It is also important that *all* variables in library functions that do not need to save state are in fact declared local. If this is not done, the variable could accidentally be used in the user's program, leading to bugs that are very difficult to track down. function lib_func(x, y, l1, l2) { ... USE VARIABLE some_var # some_var could be local ... # but is not by oversight } A different convention, common in the Tcl community, is to use a single associative array to hold the values needed by the library function(s), or "package." This significantly decreases the number of actual global names in use. For example, the functions described in *Note Reading the User Database: Passwd Functions, might have used `PW_data["inited"]', `PW_data["total"]', `PW_data["count"]' and `PW_data["awklib"]', instead of `_pw_inited', `_pw_awklib', `_pw_total', and `_pw_count'. The conventions presented in this section are exactly that, conventions. You are not required to write your programs this way, we merely recommend that you do so.  File: gawk.info, Node: Sample Programs, Next: Language History, Prev: Library Functions, Up: Top Practical `awk' Programs ************************ This chapter presents a potpourri of `awk' programs for your reading enjoyment. Many of these programs use the library functions presented in *Note A Library of `awk' Functions: Library Functions. * Menu: * Clones:: Clones of common utilities. * Miscellaneous Programs:: Some interesting `awk' programs.  File: gawk.info, Node: Clones, Next: Miscellaneous Programs, Prev: Sample Programs, Up: Sample Programs Re-inventing Wheels for Fun and Profit ====================================== This section presents a number of POSIX utilities that are implemented in `awk'. Re-inventing these programs in `awk' is often enjoyable, since the algorithms can be very clearly expressed, and usually the code is very concise and simple. This is true because `awk' does so much for you. It should be noted that these programs are not necessarily intended to replace the installed versions on your system. Instead, their purpose is to illustrate `awk' language programming for "real world" tasks. The programs are presented in alphabetical order. * Menu: * Cut Program:: The `cut' utility. * Egrep Program:: The `egrep' utility. * Id Program:: The `id' utility. * Split Program:: The `split' utility. * Tee Program:: The `tee' utility. * Uniq Program:: The `uniq' utility. * Wc Program:: The `wc' utility.  File: gawk.info, Node: Cut Program, Next: Egrep Program, Prev: Clones, Up: Clones Cutting Out Fields and Columns ------------------------------ The `cut' utility selects, or "cuts," either characters or fields from its standard input and sends them to its standard output. `cut' can cut out either a list of characters, or a list of fields. By default, fields are separated by tabs, but you may supply a command line option to change the field "delimiter", i.e. the field separator character. `cut''s definition of fields is less general than `awk''s. A common use of `cut' might be to pull out just the login name of logged-on users from the output of `who'. For example, the following pipeline generates a sorted, unique list of the logged on users: who | cut -c1-8 | sort | uniq The options for `cut' are: `-c LIST' Use LIST as the list of characters to cut out. Items within the list may be separated by commas, and ranges of characters can be separated with dashes. The list `1-8,15,22-35' specifies characters one through eight, 15, and 22 through 35. `-f LIST' Use LIST as the list of fields to cut out. `-d DELIM' Use DELIM as the field separator character instead of the tab character. `-s' Suppress printing of lines that do not contain the field delimiter. The `awk' implementation of `cut' uses the `getopt' library function (*note Processing Command Line Options: Getopt Function.), and the `join' library function (*note Merging an Array Into a String: Join Function.). The program begins with a comment describing the options and a `usage' function which prints out a usage message and exits. `usage' is called if invalid arguments are supplied. # cut.awk --- implement cut in awk # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 # Options: # -f list Cut fields # -d c Field delimiter character # -c list Cut characters # # -s Suppress lines without the delimiter character function usage( e1, e2) { e1 = "usage: cut [-f list] [-d c] [-s] [files...]" e2 = "usage: cut [-c list] [files...]" print e1 > "/dev/stderr" print e2 > "/dev/stderr" exit 1 } The variables `e1' and `e2' are used so that the function fits nicely on the screen. Next comes a `BEGIN' rule that parses the command line options. It sets `FS' to a single tab character, since that is `cut''s default field separator. The output field separator is also set to be the same as the input field separator. Then `getopt' is used to step through the command line options. One or the other of the variables `by_fields' or `by_chars' is set to true, to indicate that processing should be done by fields or by characters respectively. When cutting by characters, the output field separator is set to the null string. BEGIN \ { FS = "\t" # default OFS = FS while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) { if (c == "f") { by_fields = 1 fieldlist = Optarg } else if (c == "c") { by_chars = 1 fieldlist = Optarg OFS = "" } else if (c == "d") { if (length(Optarg) > 1) { printf("Using first character of %s" \ " for delimiter\n", Optarg) > "/dev/stderr" Optarg = substr(Optarg, 1, 1) } FS = Optarg OFS = FS if (FS == " ") # defeat awk semantics FS = "[ ]" } else if (c == "s") suppress++ else usage() } for (i = 1; i < Optind; i++) ARGV[i] = "" Special care is taken when the field delimiter is a space. Using `" "' (a single space) for the value of `FS' is incorrect--`awk' would separate fields with runs of spaces, tabs and/or newlines, and we want them to be separated with individual spaces. Also, note that after `getopt' is through, we have to clear out all the elements of `ARGV' from one to `Optind', so that `awk' will not try to process the command line options as file names. After dealing with the command line options, the program verifies that the options make sense. Only one or the other of `-c' and `-f' should be used, and both require a field list. Then either `set_fieldlist' or `set_charlist' is called to pull apart the list of fields or characters. if (by_fields && by_chars) usage() if (by_fields == 0 && by_chars == 0) by_fields = 1 # default if (fieldlist == "") { print "cut: needs list for -c or -f" > "/dev/stderr" exit 1 } if (by_fields) set_fieldlist() else set_charlist() } Here is `set_fieldlist'. It first splits the field list apart at the commas, into an array. Then, for each element of the array, it looks to see if it is actually a range, and if so splits it apart. The range is verified to make sure the first number is smaller than the second. Each number in the list is added to the `flist' array, which simply lists the fields that will be printed. Normal field splitting is used. The program lets `awk' handle the job of doing the field splitting. function set_fieldlist( n, m, i, j, k, f, g) { n = split(fieldlist, f, ",") j = 1 # index in flist for (i = 1; i <= n; i++) { if (index(f[i], "-") != 0) { # a range m = split(f[i], g, "-") if (m != 2 || g[1] >= g[2]) { printf("bad field list: %s\n", f[i]) > "/dev/stderr" exit 1 } for (k = g[1]; k <= g[2]; k++) flist[j++] = k } else flist[j++] = f[i] } nfields = j - 1 } The `set_charlist' function is more complicated than `set_fieldlist'. The idea here is to use `gawk''s `FIELDWIDTHS' variable (*note Reading Fixed-width Data: Constant Size.), which describes constant width input. When using a character list, that is exactly what we have. Setting up `FIELDWIDTHS' is more complicated than simply listing the fields that need to be printed. We have to keep track of the fields to be printed, and also the intervening characters that have to be skipped. For example, suppose you wanted characters one through eight, 15, and 22 through 35. You would use `-c 1-8,15,22-35'. The necessary value for `FIELDWIDTHS' would be `"8 6 1 6 14"'. This gives us five fields, and what should be printed are `$1', `$3', and `$5'. The intermediate fields are "filler," stuff in between the desired data. `flist' lists the fields to be printed, and `t' tracks the complete field list, including filler fields. function set_charlist( field, i, j, f, g, t, filler, last, len) { field = 1 # count total fields n = split(fieldlist, f, ",") j = 1 # index in flist for (i = 1; i <= n; i++) { if (index(f[i], "-") != 0) { # range m = split(f[i], g, "-") if (m != 2 || g[1] >= g[2]) { printf("bad character list: %s\n", f[i]) > "/dev/stderr" exit 1 } len = g[2] - g[1] + 1 if (g[1] > 1) # compute length of filler filler = g[1] - last - 1 else filler = 0 if (filler) t[field++] = filler t[field++] = len # length of field last = g[2] flist[j++] = field - 1 } else { if (f[i] > 1) filler = f[i] - last - 1 else filler = 0 if (filler) t[field++] = filler t[field++] = 1 last = f[i] flist[j++] = field - 1 } } FIELDWIDTHS = join(t, 1, field - 1) nfields = j - 1 } Here is the rule that actually processes the data. If the `-s' option was given, then `suppress' will be true. The first `if' statement makes sure that the input record does have the field separator. If `cut' is processing fields, `suppress' is true, and the field separator character is not in the record, then the record is skipped. If the record is valid, then at this point, `gawk' has split the data into fields, either using the character in `FS' or using fixed-length fields and `FIELDWIDTHS'. The loop goes through the list of fields that should be printed. If the corresponding field has data in it, it is printed. If the next field also has data, then the separator character is written out in between the fields. { if (by_fields && suppress && $0 !~ FS) next for (i = 1; i <= nfields; i++) { if ($flist[i] != "") { printf "%s", $flist[i] if (i < nfields && $flist[i+1] != "") printf "%s", OFS } } print "" } This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to do the character-based cutting. While it would be possible in other `awk' implementations to use `substr' (*note Built-in Functions for String Manipulation: String Functions.), it would also be extremely painful to do so. The `FIELDWIDTHS' variable supplies an elegant solution to the problem of picking the input line apart by characters.  File: gawk.info, Node: Egrep Program, Next: Id Program, Prev: Cut Program, Up: Clones Searching for Regular Expressions in Files ------------------------------------------ The `egrep' utility searches files for patterns. It uses regular expressions that are almost identical to those available in `awk' (*note Regular Expression Constants: Regexp Constants.). It is used this way: egrep [ OPTIONS ] 'PATTERN' FILES ... The PATTERN is a regexp. In typical usage, the regexp is quoted to prevent the shell from expanding any of the special characters as file name wildcards. Normally, `egrep' prints the lines that matched. If multiple file names are provided on the command line, each output line is preceded by the name of the file and a colon. The options are: `-c' Print out a count of the lines that matched the pattern, instead of the lines themselves. `-s' Be silent. No output is produced, and the exit value indicates whether or not the pattern was matched. `-v' Invert the sense of the test. `egrep' prints the lines that do *not* match the pattern, and exits successfully if the pattern was not matched. `-i' Ignore case distinctions in both the pattern and the input data. `-l' Only print the names of the files that matched, not the lines that matched. `-e PATTERN' Use PATTERN as the regexp to match. The purpose of the `-e' option is to allow patterns that start with a `-'. This version uses the `getopt' library function (*note Processing Command Line Options: Getopt Function.), and the file transition library program (*note Noting Data File Boundaries: Filetrans Function.). The program begins with a descriptive comment, and then a `BEGIN' rule that processes the command line arguments with `getopt'. The `-i' (ignore case) option is particularly easy with `gawk'; we just use the `IGNORECASE' built in variable (*note Built-in Variables::.). # egrep.awk --- simulate egrep in awk # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 # Options: # -c count of lines # -s silent - use exit value # -v invert test, success if no match # -i ignore case # -l print filenames only # -e argument is pattern BEGIN { while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) { if (c == "c") count_only++ else if (c == "s") no_print++ else if (c == "v") invert++ else if (c == "i") IGNORECASE = 1 else if (c == "l") filenames_only++ else if (c == "e") pattern = Optarg else usage() } Next comes the code that handles the `egrep' specific behavior. If no pattern was supplied with `-e', the first non-option on the command line is used. The `awk' command line arguments up to `ARGV[Optind]' are cleared, so that `awk' won't try to process them as files. If no files were specified, the standard input is used, and if multiple files were specified, we make sure to note this so that the file names can precede the matched lines in the output. The last two lines are commented out, since they are not needed in `gawk'. They should be uncommented if you have to use another version of `awk'. if (pattern == "") pattern = ARGV[Optind++] for (i = 1; i < Optind; i++) ARGV[i] = "" if (Optind >= ARGC) { ARGV[1] = "-" ARGC = 2 } else if (ARGC - Optind > 1) do_filenames++ # if (IGNORECASE) # pattern = tolower(pattern) } The next set of lines should be uncommented if you are not using `gawk'. This rule translates all the characters in the input line into lower-case if the `-i' option was specified. The rule is commented out since it is not necessary with `gawk'. #{ # if (IGNORECASE) # $0 = tolower($0) #} The `beginfile' function is called by the rule in `ftrans.awk' when each new file is processed. In this case, it is very simple; all it does is initialize a variable `fcount' to zero. `fcount' tracks how many lines in the current file matched the pattern. function beginfile(junk) { fcount = 0 } The `endfile' function is called after each file has been processed. It is used only when the user wants a count of the number of lines that matched. `no_print' will be true only if the exit status is desired. `count_only' will be true if line counts are desired. `egrep' will therefore only print line counts if printing and counting are enabled. The output format must be adjusted depending upon the number of files to be processed. Finally, `fcount' is added to `total', so that we know how many lines altogether matched the pattern. function endfile(file) { if (! no_print && count_only) if (do_filenames) print file ":" fcount else print fcount total += fcount } This rule does most of the work of matching lines. The variable `matches' will be true if the line matched the pattern. If the user wants lines that did not match, the sense of the `matches' is inverted using the `!' operator. `fcount' is incremented with the value of `matches', which will be either one or zero, depending upon a successful or unsuccessful match. If the line did not match, the `next' statement just moves on to the next record. There are several optimizations for performance in the following few lines of code. If the user only wants exit status (`no_print' is true), and we don't have to count lines, then it is enough to know that one line in this file matched, and we can skip on to the next file with `nextfile'. Along similar lines, if we are only printing file names, and we don't need to count lines, we can print the file name, and then skip to the next file with `nextfile'. Finally, each line is printed, with a leading filename and colon if necessary. { matches = ($0 ~ pattern) if (invert) matches = ! matches fcount += matches # 1 or 0 if (! matches) next if (no_print && ! count_only) nextfile if (filenames_only && ! count_only) { print FILENAME nextfile } if (do_filenames && ! count_only) print FILENAME ":" $0 else if (! count_only) print } The `END' rule takes care of producing the correct exit status. If there were no matches, the exit status is one, otherwise it is zero. END \ { if (total == 0) exit 1 exit 0 } The `usage' function prints a usage message in case of invalid options and then exits. function usage( e) { e = "Usage: egrep [-csvil] [-e pat] [files ...]" print e > "/dev/stderr" exit 1 } The variable `e' is used so that the function fits nicely on the printed page. Just a note on programming style. You may have noticed that the `END' rule uses backslash continuation, with the open brace on a line by itself. This is so that it more closely resembles the way functions are written. Many of the examples use this style. You can decide for yourself if you like writing your `BEGIN' and `END' rules this way, or not.  File: gawk.info, Node: Id Program, Next: Split Program, Prev: Egrep Program, Up: Clones Printing Out User Information ----------------------------- The `id' utility lists a user's real and effective user-id numbers, real and effective group-id numbers, and the user's group set, if any. `id' will only print the effective user-id and group-id if they are different from the real ones. If possible, `id' will also supply the corresponding user and group names. The output might look like this: $ id -| uid=2076(arnold) gid=10(staff) groups=10(staff),4(tty) This information is exactly what is provided by `gawk''s `/dev/user' special file (*note Special File Names in `gawk': Special Files.). However, the `id' utility provides a more palatable output than just a string of numbers. Here is a simple version of `id' written in `awk'. It uses the user database library functions (*note Reading the User Database: Passwd Functions.), and the group database library functions (*note Reading the Group Database: Group Functions.). The program is fairly straightforward. All the work is done in the `BEGIN' rule. The user and group id numbers are obtained from `/dev/user'. If there is no support for `/dev/user', the program gives up. The code is repetitive. The entry in the user database for the real user-id number is split into parts at the `:'. The name is the first field. Similar code is used for the effective user-id number, and the group numbers. # id.awk --- implement id in awk # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 # output is: # uid=12(foo) euid=34(bar) gid=3(baz) \ # egid=5(blat) groups=9(nine),2(two),1(one) BEGIN \ { if ((getline < "/dev/user") < 0) { err = "id: no /dev/user support - cannot run" print err > "/dev/stderr" exit 1 } close("/dev/user") uid = $1 euid = $2 gid = $3 egid = $4 printf("uid=%d", uid) pw = getpwuid(uid) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } if (euid != uid) { printf(" euid=%d", euid) pw = getpwuid(euid) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } } printf(" gid=%d", gid) pw = getgrgid(gid) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } if (egid != gid) { printf(" egid=%d", egid) pw = getgrgid(egid) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } } if (NF > 4) { printf(" groups="); for (i = 5; i <= NF; i++) { printf("%d", $i) pw = getgrgid($i) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } if (i < NF) printf(",") } } print "" }  File: gawk.info, Node: Split Program, Next: Tee Program, Prev: Id Program, Up: Clones Splitting a Large File Into Pieces ---------------------------------- The `split' program splits large text files into smaller pieces. By default, the output files are named `xaa', `xab', and so on. Each file has 1000 lines in it, with the likely exception of the last file. To change the number of lines in each file, you supply a number on the command line preceded with a minus, e.g., `-500' for files with 500 lines in them instead of 1000. To change the name of the output files to something like `myfileaa', `myfileab', and so on, you supply an additional argument that specifies the filename. Here is a version of `split' in `awk'. It uses the `ord' and `chr' functions presented in *Note Translating Between Characters and Numbers: Ordinal Functions. The program first sets its defaults, and then tests to make sure there are not too many arguments. It then looks at each argument in turn. The first argument could be a minus followed by a number. If it is, this happens to look like a negative number, so it is made positive, and that is the count of lines. The data file name is skipped over, and the final argument is used as the prefix for the output file names. # split.awk --- do split in awk # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 # usage: split [-num] [file] [outname] BEGIN { outfile = "x" # default count = 1000 if (ARGC > 4) usage() i = 1 if (ARGV[i] ~ /^-[0-9]+$/) { count = -ARGV[i] ARGV[i] = "" i++ } # test argv in case reading from stdin instead of file if (i in ARGV) i++ # skip data file name if (i in ARGV) { outfile = ARGV[i] ARGV[i] = "" } s1 = s2 = "a" out = (outfile s1 s2) } The next rule does most of the work. `tcount' (temporary count) tracks how many lines have been printed to the output file so far. If it is greater than `count', it is time to close the current file and start a new one. `s1' and `s2' track the current suffixes for the file name. If they are both `z', the file is just too big. Otherwise, `s1' moves to the next letter in the alphabet and `s2' starts over again at `a'. { if (++tcount > count) { close(out) if (s2 == "z") { if (s1 == "z") { printf("split: %s is too large to split\n", \ FILENAME) > "/dev/stderr" exit 1 } s1 = chr(ord(s1) + 1) s2 = "a" } else s2 = chr(ord(s2) + 1) out = (outfile s1 s2) tcount = 1 } print > out } The `usage' function simply prints an error message and exits. function usage( e) { e = "usage: split [-num] [file] [outname]" print e > "/dev/stderr" exit 1 } The variable `e' is used so that the function fits nicely on the screen. This program is a bit sloppy; it relies on `awk' to close the last file for it automatically, instead of doing it in an `END' rule.  File: gawk.info, Node: Tee Program, Next: Uniq Program, Prev: Split Program, Up: Clones Duplicating Output Into Multiple Files -------------------------------------- The `tee' program is known as a "pipe fitting." `tee' copies its standard input to its standard output, and also duplicates it to the files named on the command line. Its usage is: tee [-a] file ... The `-a' option tells `tee' to append to the named files, instead of truncating them and starting over. The `BEGIN' rule first makes a copy of all the command line arguments, into an array named `copy'. `ARGV[0]' is not copied, since it is not needed. `tee' cannot use `ARGV' directly, since `awk' will attempt to process each file named in `ARGV' as input data. If the first argument is `-a', then the flag variable `append' is set to true, and both `ARGV[1]' and `copy[1]' are deleted. If `ARGC' is less than two, then no file names were supplied, and `tee' prints a usage message and exits. Finally, `awk' is forced to read the standard input by setting `ARGV[1]' to `"-"', and `ARGC' to two. # tee.awk --- tee in awk # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 # Revised December 1995 BEGIN \ { for (i = 1; i < ARGC; i++) copy[i] = ARGV[i] if (ARGV[1] == "-a") { append = 1 delete ARGV[1] delete copy[1] ARGC-- } if (ARGC < 2) { print "usage: tee [-a] file ..." > "/dev/stderr" exit 1 } ARGV[1] = "-" ARGC = 2 } The single rule does all the work. Since there is no pattern, it is executed for each line of input. The body of the rule simply prints the line into each file on the command line, and then to the standard output. { # moving the if outside the loop makes it run faster if (append) for (i in copy) print >> copy[i] else for (i in copy) print > copy[i] print } It would have been possible to code the loop this way: for (i in copy) if (append) print >> copy[i] else print > copy[i] This is more concise, but it is also less efficient. The `if' is tested for each record and for each output file. By duplicating the loop body, the `if' is only tested once for each input record. If there are N input records and M input files, the first method only executes N `if' statements, while the second would execute N`*'M `if' statements. Finally, the `END' rule cleans up, by closing all the output files. END \ { for (i in copy) close(copy[i]) }  File: gawk.info, Node: Uniq Program, Next: Wc Program, Prev: Tee Program, Up: Clones Printing Non-duplicated Lines of Text ------------------------------------- The `uniq' utility reads sorted lines of data on its standard input, and (by default) removes duplicate lines. In other words, only unique lines are printed, hence the name. `uniq' has a number of options. The usage is: uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]] The option meanings are: `-d' Only print repeated lines. `-u' Only print non-repeated lines. `-c' Count lines. This option overrides `-d' and `-u'. Both repeated and non-repeated lines are counted. `-N' Skip N fields before comparing lines. The definition of fields is similar to `awk''s default: non-whitespace characters separated by runs of spaces and/or tabs. `+N' Skip N characters before comparing lines. Any fields specified with `-N' are skipped first. `INPUT FILE' Data is read from the input file named on the command line, instead of from the standard input. `OUTPUT FILE' The generated output is sent to the named output file, instead of to the standard output. Normally `uniq' behaves as if both the `-d' and `-u' options had been provided. Here is an `awk' implementation of `uniq'. It uses the `getopt' library function (*note Processing Command Line Options: Getopt Function.), and the `join' library function (*note Merging an Array Into a String: Join Function.). The program begins with a `usage' function and then a brief outline of the options and their meanings in a comment. The `BEGIN' rule deals with the command line arguments and options. It uses a trick to get `getopt' to handle options of the form `-25', treating such an option as the option letter `2' with an argument of `5'. If indeed two or more digits were supplied (`Optarg' looks like a number), `Optarg' is concatenated with the option digit, and then result is added to zero to make it into a number. If there is only one digit in the option, then `Optarg' is not needed, and `Optind' must be decremented so that `getopt' will process it next time. This code is admittedly a bit tricky. If no options were supplied, then the default is taken, to print both repeated and non-repeated lines. The output file, if provided, is assigned to `outputfile'. Earlier, `outputfile' was initialized to the standard output, `/dev/stdout'. # uniq.awk --- do uniq in awk # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 function usage( e) { e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]" print e > "/dev/stderr" exit 1 } # -c count lines. overrides -d and -u # -d only repeated lines # -u only non-repeated lines # -n skip n fields # +n skip n characters, skip fields first BEGIN \ { count = 1 outputfile = "/dev/stdout" opts = "udc0:1:2:3:4:5:6:7:8:9:" while ((c = getopt(ARGC, ARGV, opts)) != -1) { if (c == "u") non_repeated_only++ else if (c == "d") repeated_only++ else if (c == "c") do_count++ else if (index("0123456789", c) != 0) { # getopt requires args to options # this messes us up for things like -5 if (Optarg ~ /^[0-9]+$/) fcount = (c Optarg) + 0 else { fcount = c + 0 Optind-- } } else usage() } if (ARGV[Optind] ~ /^\+[0-9]+$/) { charcount = substr(ARGV[Optind], 2) + 0 Optind++ } for (i = 1; i < Optind; i++) ARGV[i] = "" if (repeated_only == 0 && non_repeated_only == 0) repeated_only = non_repeated_only = 1 if (ARGC - Optind == 2) { outputfile = ARGV[ARGC - 1] ARGV[ARGC - 1] = "" } } The following function, `are_equal', compares the current line, `$0', to the previous line, `last'. It handles skipping fields and characters. If no field count and no character count were specified, `are_equal' simply returns one or zero depending upon the result of a simple string comparison of `last' and `$0'. Otherwise, things get more complicated. If fields have to be skipped, each line is broken into an array using `split' (*note Built-in Functions for String Manipulation: String Functions.), and then the desired fields are joined back into a line using `join'. The joined lines are stored in `clast' and `cline'. If no fields are skipped, `clast' and `cline' are set to `last' and `$0' respectively. Finally, if characters are skipped, `substr' is used to strip off the leading `charcount' characters in `clast' and `cline'. The two strings are then compared, and `are_equal' returns the result. function are_equal( n, m, clast, cline, alast, aline) { if (fcount == 0 && charcount == 0) return (last == $0) if (fcount > 0) { n = split(last, alast) m = split($0, aline) clast = join(alast, fcount+1, n) cline = join(aline, fcount+1, m) } else { clast = last cline = $0 } if (charcount) { clast = substr(clast, charcount + 1) cline = substr(cline, charcount + 1) } return (clast == cline) } The following two rules are the body of the program. The first one is executed only for the very first line of data. It sets `last' equal to `$0', so that subsequent lines of text have something to be compared to. The second rule does the work. The variable `equal' will be one or zero depending upon the results of `are_equal''s comparison. If `uniq' is counting repeated lines, then the `count' variable is incremented if the lines are equal. Otherwise the line is printed and `count' is reset, since the two lines are not equal. If `uniq' is not counting, `count' is incremented if the lines are equal. Otherwise, if `uniq' is counting repeated lines, and more than one line has been seen, or if `uniq' is counting non-repeated lines, and only one line has been seen, then the line is printed, and `count' is reset. Finally, similar logic is used in the `END' rule to print the final line of input data. NR == 1 { last = $0 next } { equal = are_equal() if (do_count) { # overrides -d and -u if (equal) count++ else { printf("%4d %s\n", count, last) > outputfile last = $0 count = 1 # reset } next } if (equal) count++ else { if ((repeated_only && count > 1) || (non_repeated_only && count == 1)) print last > outputfile last = $0 count = 1 } } END { if (do_count) printf("%4d %s\n", count, last) > outputfile else if ((repeated_only && count > 1) || (non_repeated_only && count == 1)) print last > outputfile }  File: gawk.info, Node: Wc Program, Prev: Uniq Program, Up: Clones Counting Things --------------- The `wc' (word count) utility counts lines, words, and characters in one or more input files. Its usage is: wc [-lwc] [ FILES ... ] If no files are specified on the command line, `wc' reads its standard input. If there are multiple files, it will also print total counts for all the files. The options and their meanings are: `-l' Only count lines. `-w' Only count words. A "word" is a contiguous sequence of non-whitespace characters, separated by spaces and/or tabs. Happily, this is the normal way `awk' separates fields in its input data. `-c' Only count characters. Implementing `wc' in `awk' is particularly elegant, since `awk' does a lot of the work for us; it splits lines into words (i.e. fields) and counts them, it counts lines (i.e. records) for us, and it can easily tell us how long a line is. This version uses the `getopt' library function (*note Processing Command Line Options: Getopt Function.), and the file transition functions (*note Noting Data File Boundaries: Filetrans Function.). This version has one major difference from traditional versions of `wc'. Our version always prints the counts in the order lines, words, and characters. Traditional versions note the order of the `-l', `-w', and `-c' options on the command line, and print the counts in that order. The `BEGIN' rule does the argument processing. The variable `print_total' will be true if more than one file was named on the command line. # wc.awk --- count lines, words, characters # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 # Options: # -l only count lines # -w only count words # -c only count characters # # Default is to count lines, words, characters BEGIN { # let getopt print a message about # invalid options. we ignore them while ((c = getopt(ARGC, ARGV, "lwc")) != -1) { if (c == "l") do_lines = 1 else if (c == "w") do_words = 1 else if (c == "c") do_chars = 1 } for (i = 1; i < Optind; i++) ARGV[i] = "" # if no options, do all if (! do_lines && ! do_words && ! do_chars) do_lines = do_words = do_chars = 1 print_total = (ARGC - i > 2) } The `beginfile' function is simple; it just resets the counts of lines, words, and characters to zero, and saves the current file name in `fname'. The `endfile' function adds the current file's numbers to the running totals of lines, words, and characters. It then prints out those numbers for the file that was just read. It relies on `beginfile' to reset the numbers for the following data file. function beginfile(file) { chars = lines = words = 0 fname = FILENAME } function endfile(file) { tchars += chars tlines += lines twords += words if (do_lines) printf "\t%d", lines if (do_words) printf "\t%d", words if (do_chars) printf "\t%d", chars printf "\t%s\n", fname } There is one rule that is executed for each line. It adds the length of the record to `chars'. It has to add one, since the newline character separating records (the value of `RS') is not part of the record itself. `lines' is incremented for each line read, and `words' is incremented by the value of `NF', the number of "words" on this line.(1) Finally, the `END' rule simply prints the totals for all the files. # do per line { chars += length($0) + 1 # get newline lines++ words += NF } END { if (print_total) { if (do_lines) printf "\t%d", tlines if (do_words) printf "\t%d", twords if (do_chars) printf "\t%d", tchars print "\ttotal" } } ---------- Footnotes ---------- (1) Examine the code in *Note Noting Data File Boundaries: Filetrans Function. Why must `wc' use a separate `lines' variable, instead of using the value of `FNR' in `endfile'?  File: gawk.info, Node: Miscellaneous Programs, Prev: Clones, Up: Sample Programs A Grab Bag of `awk' Programs ============================ This section is a large "grab bag" of miscellaneous programs. We hope you find them both interesting and enjoyable. * Menu: * Dupword Program:: Finding duplicated words in a document. * Alarm Program:: An alarm clock. * Translate Program:: A program similar to the `tr' utility. * Labels Program:: Printing mailing labels. * Word Sorting:: A program to produce a word usage count. * History Sorting:: Eliminating duplicate entries from a history file. * Extract Program:: Pulling out programs from Texinfo source files. * Simple Sed:: A Simple Stream Editor. * Igawk Program:: A wrapper for `awk' that includes files.  File: gawk.info, Node: Dupword Program, Next: Alarm Program, Prev: Miscellaneous Programs, Up: Miscellaneous Programs Finding Duplicated Words in a Document -------------------------------------- A common error when writing large amounts of prose is to accidentally duplicate words. Often you will see this in text as something like "the the program does the following ...." When the text is on-line, often the duplicated words occur at the end of one line and the beginning of another, making them very difficult to spot. This program, `dupword.awk', scans through a file one line at a time, and looks for adjacent occurrences of the same word. It also saves the last word on a line (in the variable `prev') for comparison with the first word on the next line. The first two statements make sure that the line is all lower-case, so that, for example, "The" and "the" compare equal to each other. The second statement removes all non-alphanumeric and non-whitespace characters from the line, so that punctuation does not affect the comparison either. This sometimes leads to reports of duplicated words that really are different, but this is unusual. # dupword --- find duplicate words in text # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # December 1991 { $0 = tolower($0) gsub(/[^A-Za-z0-9 \t]/, ""); if ($1 == prev) printf("%s:%d: duplicate %s\n", FILENAME, FNR, $1) for (i = 2; i <= NF; i++) if ($i == $(i-1)) printf("%s:%d: duplicate %s\n", FILENAME, FNR, $i) prev = $NF }  File: gawk.info, Node: Alarm Program, Next: Translate Program, Prev: Dupword Program, Up: Miscellaneous Programs An Alarm Clock Program ---------------------- The following program is a simple "alarm clock" program. You give it a time of day, and an optional message. At the given time, it prints the message on the standard output. In addition, you can give it the number of times to repeat the message, and also a delay between repetitions. This program uses the `gettimeofday' function from *Note Managing the Time of Day: Gettimeofday Function. All the work is done in the `BEGIN' rule. The first part is argument checking and setting of defaults; the delay, the count, and the message to print. If the user supplied a message, but it does not contain the ASCII BEL character (known as the "alert" character, `\a'), then it is added to the message. (On many systems, printing the ASCII BEL generates some sort of audible alert. Thus, when the alarm goes off, the system calls attention to itself, in case the user is not looking at their computer or terminal.) # alarm --- set an alarm # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 # usage: alarm time [ "message" [ count [ delay ] ] ] BEGIN \ { # Initial argument sanity checking usage1 = "usage: alarm time ['message' [count [delay]]]" usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1]) if (ARGC < 2) { print usage > "/dev/stderr" exit 1 } else if (ARGC == 5) { delay = ARGV[4] + 0 count = ARGV[3] + 0 message = ARGV[2] } else if (ARGC == 4) { count = ARGV[3] + 0 message = ARGV[2] } else if (ARGC == 3) { message = ARGV[2] } else if (ARGV[1] !~ /[0-9]?[0-9]:[0-9][0-9]/) { print usage1 > "/dev/stderr" print usage2 > "/dev/stderr" exit 1 } # set defaults for once we reach the desired time if (delay == 0) delay = 180 # 3 minutes if (count == 0) count = 5 if (message == "") message = sprintf("\aIt is now %s!\a", ARGV[1]) else if (index(message, "\a") == 0) message = "\a" message "\a" The next section of code turns the alarm time into hours and minutes, and converts it if necessary to a 24-hour clock. Then it turns that time into a count of the seconds since midnight. Next it turns the current time into a count of seconds since midnight. The difference between the two is how long to wait before setting off the alarm. # split up dest time split(ARGV[1], atime, ":") hour = atime[1] + 0 # force numeric minute = atime[2] + 0 # force numeric # get current broken down time gettimeofday(now) # if time given is 12-hour hours and it's after that # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m., # then add 12 to real hour if (hour < 12 && now["hour"] > hour) hour += 12 # set target time in seconds since midnight target = (hour * 60 * 60) + (minute * 60) # get current time in seconds since midnight current = (now["hour"] * 60 * 60) + \ (now["minute"] * 60) + now["second"] # how long to sleep for naptime = target - current if (naptime <= 0) { print "time is in the past!" > "/dev/stderr" exit 1 } Finally, the program uses the `system' function (*note Built-in Functions for Input/Output: I/O Functions.) to call the `sleep' utility. The `sleep' utility simply pauses for the given number of seconds. If the exit status is not zero, the program assumes that `sleep' was interrupted, and exits. If `sleep' exited with an OK status (zero), then the program prints the message in a loop, again using `sleep' to delay for however many seconds are necessary. # zzzzzz..... go away if interrupted if (system(sprintf("sleep %d", naptime)) != 0) exit 1 # time to notify! command = sprintf("sleep %d", delay) for (i = 1; i <= count; i++) { print message # if sleep command interrupted, go away if (system(command) != 0) break } exit 0 }  File: gawk.info, Node: Translate Program, Next: Labels Program, Prev: Alarm Program, Up: Miscellaneous Programs Transliterating Characters -------------------------- The system `tr' utility transliterates characters. For example, it is often used to map upper-case letters into lower-case, for further processing. GENERATE DATA | tr '[A-Z]' '[a-z]' | PROCESS DATA ... You give `tr' two lists of characters enclosed in square brackets. Usually, the lists are quoted to keep the shell from attempting to do a filename expansion.(1) When processing the input, the first character in the first list is replaced with the first character in the second list, the second character in the first list is replaced with the second character in the second list, and so on. If there are more characters in the "from" list than in the "to" list, the last character of the "to" list is used for the remaining characters in the "from" list. Some time ago, a user proposed to us that we add a transliteration function to `gawk'. Being opposed to "creeping featurism," I wrote the following program to prove that character transliteration could be done with a user-level function. This program is not as complete as the system `tr' utility, but it will do most of the job. The `translate' program demonstrates one of the few weaknesses of standard `awk': dealing with individual characters is very painful, requiring repeated use of the `substr', `index', and `gsub' built-in functions (*note Built-in Functions for String Manipulation: String Functions.).(2) There are two functions. The first, `stranslate', takes three arguments. `from' A list of characters to translate from. `to' A list of characters to translate to. `target' The string to do the translation on. Associative arrays make the translation part fairly easy. `t_ar' holds the "to" characters, indexed by the "from" characters. Then a simple loop goes through `from', one character at a time. For each character in `from', if the character appears in `target', `gsub' is used to change it to the corresponding `to' character. The `translate' function simply calls `stranslate' using `$0' as the target. The main program sets two global variables, `FROM' and `TO', from the command line, and then changes `ARGV' so that `awk' will read from the standard input. Finally, the processing rule simply calls `translate' for each record. # translate --- do tr like stuff # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # August 1989 # bugs: does not handle things like: tr A-Z a-z, it has # to be spelled out. However, if `to' is shorter than `from', # the last character in `to' is used for the rest of `from'. function stranslate(from, to, target, lf, lt, t_ar, i, c) { lf = length(from) lt = length(to) for (i = 1; i <= lt; i++) t_ar[substr(from, i, 1)] = substr(to, i, 1) if (lt < lf) for (; i <= lf; i++) t_ar[substr(from, i, 1)] = substr(to, lt, 1) for (i = 1; i <= lf; i++) { c = substr(from, i, 1) if (index(target, c) > 0) gsub(c, t_ar[c], target) } return target } function translate(from, to) { return $0 = stranslate(from, to, $0) } # main program BEGIN { if (ARGC < 3) { print "usage: translate from to" > "/dev/stderr" exit } FROM = ARGV[1] TO = ARGV[2] ARGC = 2 ARGV[1] = "-" } { translate(FROM, TO) print } While it is possible to do character transliteration in a user-level function, it is not necessarily efficient, and we started to consider adding a built-in function. However, shortly after writing this program, we learned that the System V Release 4 `awk' had added the `toupper' and `tolower' functions. These functions handle the vast majority of the cases where character transliteration is necessary, and so we chose to simply add those functions to `gawk' as well, and then leave well enough alone. An obvious improvement to this program would be to set up the `t_ar' array only once, in a `BEGIN' rule. However, this assumes that the "from" and "to" lists will never change throughout the lifetime of the program. ---------- Footnotes ---------- (1) On older, non-POSIX systems, `tr' often does not require that the lists be enclosed in square brackets and quoted. This is a feature. (2) This program was written before `gawk' acquired the ability to split each character in a string into separate array elements. How might this ability simplify the program?  File: gawk.info, Node: Labels Program, Next: Word Sorting, Prev: Translate Program, Up: Miscellaneous Programs Printing Mailing Labels ----------------------- Here is a "real world"(1) program. This script reads lists of names and addresses, and generates mailing labels. Each page of labels has 20 labels on it, two across and ten down. The addresses are guaranteed to be no more than five lines of data. Each address is separated from the next by a blank line. The basic idea is to read 20 labels worth of data. Each line of each label is stored in the `line' array. The single rule takes care of filling the `line' array and printing the page when 20 labels have been read. The `BEGIN' rule simply sets `RS' to the empty string, so that `awk' will split records at blank lines (*note How Input is Split into Records: Records.). It sets `MAXLINES' to 100, since `MAXLINE' is the maximum number of lines on the page (20 * 5 = 100). Most of the work is done in the `printpage' function. The label lines are stored sequentially in the `line' array. But they have to be printed horizontally; `line[1]' next to `line[6]', `line[2]' next to `line[7]', and so on. Two loops are used to accomplish this. The outer loop, controlled by `i', steps through every 10 lines of data; this is each row of labels. The inner loop, controlled by `j', goes through the lines within the row. As `j' goes from zero to four, `i+j' is the `j''th line in the row, and `i+j+5' is the entry next to it. The output ends up looking something like this: line 1 line 6 line 2 line 7 line 3 line 8 line 4 line 9 line 5 line 10 As a final note, at lines 21 and 61, an extra blank line is printed, to keep the output lined up on the labels. This is dependent on the particular brand of labels in use when the program was written. You will also note that there are two blank lines at the top and two blank lines at the bottom. The `END' rule arranges to flush the final page of labels; there may not have been an even multiple of 20 labels in the data. # labels.awk # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # June 1992 # Program to print labels. Each label is 5 lines of data # that may have blank lines. The label sheets have 2 # blank lines at the top and 2 at the bottom. BEGIN { RS = "" ; MAXLINES = 100 } function printpage( i, j) { if (Nlines <= 0) return printf "\n\n" # header for (i = 1; i <= Nlines; i += 10) { if (i == 21 || i == 61) print "" for (j = 0; j < 5; j++) { if (i + j > MAXLINES) break printf " %-41s %s\n", line[i+j], line[i+j+5] } print "" } printf "\n\n" # footer for (i in line) line[i] = "" } # main rule { if (Count >= 20) { printpage() Count = 0 Nlines = 0 } n = split($0, a, "\n") for (i = 1; i <= n; i++) line[++Nlines] = a[i] for (; i <= 5; i++) line[++Nlines] = "" Count++ } END \ { printpage() } ---------- Footnotes ---------- (1) "Real world" is defined as "a program actually used to get something done."  File: gawk.info, Node: Word Sorting, Next: History Sorting, Prev: Labels Program, Up: Miscellaneous Programs Generating Word Usage Counts ---------------------------- The following `awk' program prints the number of occurrences of each word in its input. It illustrates the associative nature of `awk' arrays by using strings as subscripts. It also demonstrates the `for X in ARRAY' construction. Finally, it shows how `awk' can be used in conjunction with other utility programs to do a useful task of some complexity with a minimum of effort. Some explanations follow the program listing. awk ' # Print list of word frequencies { for (i = 1; i <= NF; i++) freq[$i]++ } END { for (word in freq) printf "%s\t%d\n", word, freq[word] }' The first thing to notice about this program is that it has two rules. The first rule, because it has an empty pattern, is executed on every line of the input. It uses `awk''s field-accessing mechanism (*note Examining Fields: Fields.) to pick out the individual words from the line, and the built-in variable `NF' (*note Built-in Variables::.) to know how many fields are available. For each input word, an element of the array `freq' is incremented to reflect that the word has been seen an additional time. The second rule, because it has the pattern `END', is not executed until the input has been exhausted. It prints out the contents of the `freq' table that has been built up inside the first action. This program has several problems that would prevent it from being useful by itself on real text files: * Words are detected using the `awk' convention that fields are separated by whitespace and that other characters in the input (except newlines) don't have any special meaning to `awk'. This means that punctuation characters count as part of words. * The `awk' language considers upper- and lower-case characters to be distinct. Therefore, `bartender' and `Bartender' are not treated as the same word. This is undesirable since, in normal text, words are capitalized if they begin sentences, and a frequency analyzer should not be sensitive to capitalization. * The output does not come out in any useful order. You're more likely to be interested in which words occur most frequently, or having an alphabetized table of how frequently each word occurs. The way to solve these problems is to use some of the more advanced features of the `awk' language. First, we use `tolower' to remove case distinctions. Next, we use `gsub' to remove punctuation characters. Finally, we use the system `sort' utility to process the output of the `awk' script. Here is the new version of the program: # Print list of word frequencies { $0 = tolower($0) # remove case distinctions gsub(/[^a-z0-9_ \t]/, "", $0) # remove punctuation for (i = 1; i <= NF; i++) freq[$i]++ } END { for (word in freq) printf "%s\t%d\n", word, freq[word] } Assuming we have saved this program in a file named `wordfreq.awk', and that the data is in `file1', the following pipeline awk -f wordfreq.awk file1 | sort +1 -nr produces a table of the words appearing in `file1' in order of decreasing frequency. The `awk' program suitably massages the data and produces a word frequency table, which is not ordered. The `awk' script's output is then sorted by the `sort' utility and printed on the terminal. The options given to `sort' in this example specify to sort using the second field of each input line (skipping one field), that the sort keys should be treated as numeric quantities (otherwise `15' would come before `5'), and that the sorting should be done in descending (reverse) order. We could have even done the `sort' from within the program, by changing the `END' action to: END { sort = "sort +1 -nr" for (word in freq) printf "%s\t%d\n", word, freq[word] | sort close(sort) } You would have to use this way of sorting on systems that do not have true pipes. See the general operating system documentation for more information on how to use the `sort' program.  File: gawk.info, Node: History Sorting, Next: Extract Program, Prev: Word Sorting, Up: Miscellaneous Programs Removing Duplicates from Unsorted Text -------------------------------------- The `uniq' program (*note Printing Non-duplicated Lines of Text: Uniq Program.), removes duplicate lines from *sorted* data. Suppose, however, you need to remove duplicate lines from a data file, but that you wish to preserve the order the lines are in? A good example of this might be a shell history file. The history file keeps a copy of all the commands you have entered, and it is not unusual to repeat a command several times in a row. Occasionally you might wish to compact the history by removing duplicate entries. Yet it is desirable to maintain the order of the original commands. This simple program does the job. It uses two arrays. The `data' array is indexed by the text of each line. For each line, `data[$0]' is incremented. If a particular line has not been seen before, then `data[$0]' will be zero. In that case, the text of the line is stored in `lines[count]'. Each element of `lines' is a unique command, and the indices of `lines' indicate the order in which those lines were encountered. The `END' rule simply prints out the lines, in order. # histsort.awk --- compact a shell history file # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 # Thanks to Byron Rakitzis for the general idea { if (data[$0]++ == 0) lines[++count] = $0 } END { for (i = 1; i <= count; i++) print lines[i] } This program also provides a foundation for generating other useful information. For example, using the following `print' satement in the `END' rule would indicate how often a particular command was used. print data[lines[i]], lines[i] This works because `data[$0]' was incremented each time a line was seen.  File: gawk.info, Node: Extract Program, Next: Simple Sed, Prev: History Sorting, Up: Miscellaneous Programs Extracting Programs from Texinfo Source Files --------------------------------------------- The nodes *Note A Library of `awk' Functions: Library Functions, and *Note Practical `awk' Programs: Sample Programs, are the top level nodes for a large number of `awk' programs. If you wish to experiment with these programs, it is tedious to have to type them in by hand. Here we present a program that can extract parts of a Texinfo input file into separate files. This Info file is written in Texinfo, the GNU project's document formatting language. A single Texinfo source file can be used to produce both printed and on-line documentation. The Texinfo language is described fully, starting with *Note Introduction: (texi)Top. For our purposes, it is enough to know three things about Texinfo input files. * The "at" symbol, `@@', is special in Texinfo, much like `\' in C or `awk'. Literal `@@' symbols are represented in Texinfo source files as `@@@@'. * Comments start with either `@@c' or `@@comment'. The file extraction program will work by using special comments that start at the beginning of a line. * Example text that should not be split across a page boundary is bracketed between lines containing `@@group' and `@@end group' commands. The following program, `extract.awk', reads through a Texinfo source file, and does two things, based on the special comments. Upon seeing `@@c system ...', it runs a command, by extracting the command text from the control line and passing it on to the `system' function (*note Built-in Functions for Input/Output: I/O Functions.). Upon seeing `@@c file FILENAME', each subsequent line is sent to the file FILENAME, until `@@c endfile' is encountered. The rules in `extract.awk' will match either `@@c' or `@@comment' by letting the `omment' part be optional. Lines containing `@@group' and `@@end group' are simply removed. `extract.awk' uses the `join' library function (*note Merging an Array Into a String: Join Function.). The example programs in the on-line Texinfo source for `Effective AWK Programming' (`gawk.texi') have all been bracketed inside `file', and `endfile' lines. The `gawk' distribution uses a copy of `extract.awk' to extract the sample programs and install many of them in a standard directory, where `gawk' can find them. `extract.awk' begins by setting `IGNORECASE' to one, so that mixed upper-case and lower-case letters in the directives won't matter. The first rule handles calling `system', checking that a command was given (`NF' is at least three), and also checking that the command exited with a zero exit status, signifying OK. # extract.awk --- extract files and run programs # from texinfo files # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # May 1993 BEGIN { IGNORECASE = 1 } /^@@c(omment)?[ \t]+system/ \ { if (NF < 3) { e = (FILENAME ":" FNR) e = (e ": badly formed `system' line") print e > "/dev/stderr" next } $1 = "" $2 = "" stat = system($0) if (stat != 0) { e = (FILENAME ":" FNR) e = (e ": warning: system returned " stat) print e > "/dev/stderr" } } The variable `e' is used so that the function fits nicely on the screen. The second rule handles moving data into files. It verifies that a file name was given in the directive. If the file named is not the current file, then the current file is closed. This means that an `@@c endfile' was not given for that file. (We should probably print a diagnostic in this case, although at the moment we do not.) The `for' loop does the work. It reads lines using `getline' (*note Explicit Input with `getline': Getline.). For an unexpected end of file, it calls the `unexpected_eof' function. If the line is an "endfile" line, then it breaks out of the loop. If the line is an `@@group' or `@@end group' line, then it ignores it, and goes on to the next line. Most of the work is in the following few lines. If the line has no `@@' symbols, it can be printed directly. Otherwise, each leading `@@' must be stripped off. To remove the `@@' symbols, the line is split into separate elements of the array `a', using the `split' function (*note Built-in Functions for String Manipulation: String Functions.). Each element of `a' that is empty indicates two successive `@@' symbols in the original line. For each two empty elements (`@@@@' in the original file), we have to add back in a single `@@' symbol. When the processing of the array is finished, `join' is called with the value of `SUBSEP', to rejoin the pieces back into a single line. That line is then printed to the output file. /^@@c(omment)?[ \t]+file/ \ { if (NF != 3) { e = (FILENAME ":" FNR ": badly formed `file' line") print e > "/dev/stderr" next } if ($3 != curfile) { if (curfile != "") close(curfile) curfile = $3 } for (;;) { if ((getline line) <= 0) unexpected_eof() if (line ~ /^@@c(omment)?[ \t]+endfile/) break else if (line ~ /^@@(end[ \t]+)?group/) continue if (index(line, "@@") == 0) { print line > curfile continue } n = split(line, a, "@@") # if a[1] == "", means leading @@, # don't add one back in. for (i = 2; i <= n; i++) { if (a[i] == "") { # was an @@@@ a[i] = "@@" if (a[i+1] == "") i++ } } print join(a, 1, n, SUBSEP) > curfile } } An important thing to note is the use of the `>' redirection. Output done with `>' only opens the file once; it stays open and subsequent output is appended to the file (*note Redirecting Output of `print' and `printf': Redirection.). This allows us to easily mix program text and explanatory prose for the same sample source file (as has been done here!) without any hassle. The file is only closed when a new data file name is encountered, or at the end of the input file. Finally, the function `unexpected_eof' prints an appropriate error message and then exits. The `END' rule handles the final cleanup, closing the open file. function unexpected_eof() { printf("%s:%d: unexpected EOF or error\n", \ FILENAME, FNR) > "/dev/stderr" exit 1 } END { if (curfile) close(curfile) }  File: gawk.info, Node: Simple Sed, Next: Igawk Program, Prev: Extract Program, Up: Miscellaneous Programs A Simple Stream Editor ---------------------- The `sed' utility is a "stream editor," a program that reads a stream of data, makes changes to it, and passes the modified data on. It is often used to make global changes to a large file, or to a stream of data generated by a pipeline of commands. While `sed' is a complicated program in its own right, its most common use is to perform global substitutions in the middle of a pipeline: command1 < orig.data | sed 's/old/new/g' | command2 > result Here, the `s/old/new/g' tells `sed' to look for the regexp `old' on each input line, and replace it with the text `new', globally (i.e. all the occurrences on a line). This is similar to `awk''s `gsub' function (*note Built-in Functions for String Manipulation: String Functions.). The following program, `awksed.awk', accepts at least two command line arguments; the pattern to look for and the text to replace it with. Any additional arguments are treated as data file names to process. If none are provided, the standard input is used. # awksed.awk --- do s/foo/bar/g using just print # Thanks to Michael Brennan for the idea # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # August 1995 function usage() { print "usage: awksed pat repl [files...]" > "/dev/stderr" exit 1 } BEGIN { # validate arguments if (ARGC < 3) usage() RS = ARGV[1] ORS = ARGV[2] # don't use arguments as files ARGV[1] = ARGV[2] = "" } # look ma, no hands! { if (RT == "") printf "%s", $0 else print } The program relies on `gawk''s ability to have `RS' be a regexp and on the setting of `RT' to the actual text that terminated the record (*note How Input is Split into Records: Records.). The idea is to have `RS' be the pattern to look for. `gawk' will automatically set `$0' to the text between matches of the pattern. This is text that we wish to keep, unmodified. Then, by setting `ORS' to the replacement text, a simple `print' statement will output the text we wish to keep, followed by the replacement text. There is one wrinkle to this scheme, which is what to do if the last record doesn't end with text that matches `RS'? Using a `print' statement unconditionally prints the replacement text, which is not correct. However, if the file did not end in text that matches `RS', `RT' will be set to the null string. In this case, we can print `$0' using `printf' (*note Using `printf' Statements for Fancier Printing: Printf.). The `BEGIN' rule handles the setup, checking for the right number of arguments, and calling `usage' if there is a problem. Then it sets `RS' and `ORS' from the command line arguments, and sets `ARGV[1]' and `ARGV[2]' to the null string, so that they will not be treated as file names (*note Using `ARGC' and `ARGV': ARGC and ARGV.). The `usage' function prints an error message and exits. Finally, the single rule handles the printing scheme outlined above, using `print' or `printf' as appropriate, depending upon the value of `RT'.  File: gawk.info, Node: Igawk Program, Prev: Simple Sed, Up: Miscellaneous Programs An Easy Way to Use Library Functions ------------------------------------ Using library functions in `awk' can be very beneficial. It encourages code re-use and the writing of general functions. Programs are smaller, and therefore clearer. However, using library functions is only easy when writing `awk' programs; it is painful when running them, requiring multiple `-f' options. If `gawk' is unavailable, then so too is the `AWKPATH' environment variable and the ability to put `awk' functions into a library directory (*note Command Line Options: Options.). It would be nice to be able to write programs like so: # library functions @@include getopt.awk @@include join.awk ... # main program BEGIN { while ((c = getopt(ARGC, ARGV, "a:b:cde")) != -1) ... ... } The following program, `igawk.sh', provides this service. It simulates `gawk''s searching of the `AWKPATH' variable, and also allows "nested" includes; i.e. a file that has been included with `@@include' can contain further `@@include' statements. `igawk' will make an effort to only include files once, so that nested includes don't accidentally include a library function twice. `igawk' should behave externally just like `gawk'. This means it should accept all of `gawk''s command line arguments, including the ability to have multiple source files specified via `-f', and the ability to mix command line and library source files. The program is written using the POSIX Shell (`sh') command language. The way the program works is as follows: 1. Loop through the arguments, saving anything that doesn't represent `awk' source code for later, when the expanded program is run. 2. For any arguments that do represent `awk' text, put the arguments into a temporary file that will be expanded. There are two cases. a. Literal text, provided with `--source' or `--source='. This text is just echoed directly. The `echo' program will automatically supply a trailing newline. b. File names provided with `-f'. We use a neat trick, and echo `@@include FILENAME' into the temporary file. Since the file inclusion program will work the way `gawk' does, this will get the text of the file included into the program at the correct point. 3. Run an `awk' program (naturally) over the temporary file to expand `@@include' statements. The expanded program is placed in a second temporary file. 4. Run the expanded program with `gawk' and any other original command line arguments that the user supplied (such as the data file names). The initial part of the program turns on shell tracing if the first argument was `debug'. Otherwise, a shell `trap' statement arranges to clean up any temporary files on program exit or upon an interrupt. The next part loops through all the command line arguments. There are several cases of interest. `--' This ends the arguments to `igawk'. Anything else should be passed on to the user's `awk' program without being evaluated. `-W' This indicates that the next option is specific to `gawk'. To make argument processing easier, the `-W' is appended to the front of the remaining arguments and the loop continues. (This is an `sh' programming trick. Don't worry about it if you are not familiar with `sh'.) `-v' `-F' These are saved and passed on to `gawk'. `-f' `--file' `--file=' `-Wfile=' The file name is saved to the temporary file `/tmp/ig.s.$$' with an `@@include' statement. The `sed' utility is used to remove the leading option part of the argument (e.g., `--file='). `--source' `--source=' `-Wsource=' The source text is echoed into `/tmp/ig.s.$$'. `--version' `--version' `-Wversion' `igawk' prints its version number, and runs `gawk --version' to get the `gawk' version information, and then exits. If none of `-f', `--file', `-Wfile', `--source', or `-Wsource', were supplied, then the first non-option argument should be the `awk' program. If there are no command line arguments left, `igawk' prints an error message and exits. Otherwise, the first argument is echoed into `/tmp/ig.s.$$'. In any case, after the arguments have been processed, `/tmp/ig.s.$$' contains the complete text of the original `awk' program. The `$$' in `sh' represents the current process ID number. It is often used in shell programs to generate unique temporary file names. This allows multiple users to run `igawk' without worrying that the temporary file names will clash. Here's the program: #! /bin/sh # igawk --- like gawk but do @@include processing # Arnold Robbins, arnold@@gnu.ai.mit.edu, Public Domain # July 1993 if [ "$1" = debug ] then set -x shift else # cleanup on exit, hangup, interrupt, quit, termination trap 'rm -f /tmp/ig.[se].$$' 0 1 2 3 15 fi while [ $# -ne 0 ] # loop over arguments do case $1 in --) shift; break;; -W) shift set -- -W"$@@" continue;; -[vF]) opts="$opts $1 '$2'" shift;; -[vF]*) opts="$opts '$1'" ;; -f) echo @@include "$2" >> /tmp/ig.s.$$ shift;; -f*) f=`echo "$1" | sed 's/-f//'` echo @@include "$f" >> /tmp/ig.s.$$ ;; -?file=*) # -Wfile or --file f=`echo "$1" | sed 's/-.file=//'` echo @@include "$f" >> /tmp/ig.s.$$ ;; -?file) # get arg, $2 echo @@include "$2" >> /tmp/ig.s.$$ shift;; -?source=*) # -Wsource or --source t=`echo "$1" | sed 's/-.source=//'` echo "$t" >> /tmp/ig.s.$$ ;; -?source) # get arg, $2 echo "$2" >> /tmp/ig.s.$$ shift;; -?version) echo igawk: version 1.0 1>&2 gawk --version exit 0 ;; -[W-]*) opts="$opts '$1'" ;; *) break;; esac shift done if [ ! -s /tmp/ig.s.$$ ] then if [ -z "$1" ] then echo igawk: no program! 1>&2 exit 1 else echo "$1" > /tmp/ig.s.$$ shift fi fi # at this point, /tmp/ig.s.$$ has the program The `awk' program to process `@@include' directives reads through the program, one line at a time using `getline' (*note Explicit Input with `getline': Getline.). The input file names and `@@include' statements are managed using a stack. As each `@@include' is encountered, the current file name is "pushed" onto the stack, and the file named in the `@@include' directive becomes the current file name. As each file is finished, the stack is "popped," and the previous input file becomes the current input file again. The process is started by making the original file the first one on the stack. The `pathto' function does the work of finding the full path to a file. It simulates `gawk''s behavior when searching the `AWKPATH' environment variable (*note The `AWKPATH' Environment Variable: AWKPATH Variable.). If a file name has a `/' in it, no path search is done. Otherwise, the file name is concatenated with the name of each directory in the path, and an attempt is made to open the generated file name. The only way in `awk' to test if a file can be read is to go ahead and try to read it with `getline'; that is what `pathto' does.(1) If the file can be read, it is closed, and the file name is returned. gawk -- ' # process @@include directives function pathto(file, i, t, junk) { if (index(file, "/") != 0) return file for (i = 1; i <= ndirs; i++) { t = (pathlist[i] "/" file) if ((getline junk < t) > 0) { # found it close(t) return t } } return "" } The main program is contained inside one `BEGIN' rule. The first thing it does is set up the `pathlist' array that `pathto' uses. After splitting the path on `:', null elements are replaced with `"."', which represents the current directory. BEGIN { path = ENVIRON["AWKPATH"] ndirs = split(path, pathlist, ":") for (i = 1; i <= ndirs; i++) { if (pathlist[i] == "") pathlist[i] = "." } The stack is initialized with `ARGV[1]', which will be `/tmp/ig.s.$$'. The main loop comes next. Input lines are read in succession. Lines that do not start with `@@include' are printed verbatim. If the line does start with `@@include', the file name is in `$2'. `pathto' is called to generate the full path. If it could not, then we print an error message and continue. The next thing to check is if the file has been included already. The `processed' array is indexed by the full file name of each included file, and it tracks this information for us. If the file has been seen, a warning message is printed. Otherwise, the new file name is pushed onto the stack and processing continues. Finally, when `getline' encounters the end of the input file, the file is closed and the stack is popped. When `stackptr' is less than zero, the program is done. stackptr = 0 input[stackptr] = ARGV[1] # ARGV[1] is first file for (; stackptr >= 0; stackptr--) { while ((getline < input[stackptr]) > 0) { if (tolower($1) != "@@include") { print continue } fpath = pathto($2) if (fpath == "") { printf("igawk:%s:%d: cannot find %s\n", \ input[stackptr], FNR, $2) > "/dev/stderr" continue } if (! (fpath in processed)) { processed[fpath] = input[stackptr] input[++stackptr] = fpath } else print $2, "included in", input[stackptr], \ "already included in", \ processed[fpath] > "/dev/stderr" } close(input[stackptr]) } }' /tmp/ig.s.$$ > /tmp/ig.e.$$ The last step is to call `gawk' with the expanded program and the original options and command line arguments that the user supplied. `gawk''s exit status is passed back on to `igawk''s calling program. eval gawk -f /tmp/ig.e.$$ $opts -- "$@@" exit $? This version of `igawk' represents my third attempt at this program. There are three key simplifications that made the program work better. 1. Using `@@include' even for the files named with `-f' makes building the initial collected `awk' program much simpler; all the `@@include' processing can be done once. 2. The `pathto' function doesn't try to save the line read with `getline' when testing for the file's accessibility. Trying to save this line for use with the main program complicates things considerably. 3. Using a `getline' loop in the `BEGIN' rule does it all in one place. It is not necessary to call out to a separate loop for processing nested `@@include' statements. Also, this program illustrates that it is often worthwhile to combine `sh' and `awk' programming together. You can usually accomplish quite a lot, without having to resort to low-level programming in C or C++, and it is frequently easier to do certain kinds of string and argument manipulation using the shell than it is in `awk'. Finally, `igawk' shows that it is not always necessary to add new features to a program; they can often be layered on top. With `igawk', there is no real reason to build `@@include' processing into `gawk' itself. As an additional example of this, consider the idea of having two files in a directory in the search path. `default.awk' This file would contain a set of default library functions, such as `getopt' and `assert'. `site.awk' This file would contain library functions that are specific to a site or installation, i.e. locally developed functions. Having a separate file allows `default.awk' to change with new `gawk' releases, without requiring the system administrator to update it each time by adding the local functions. One user suggested that `gawk' be modified to automatically read these files upon startup. Instead, it would be very simple to modify `igawk' to do this. Since `igawk' can process nested `@@include' directives, `default.awk' could simply contain `@@include' statements for the desired library functions. ---------- Footnotes ---------- (1) On some very old versions of `awk', the test `getline junk < t' can loop forever if the file exists but is empty. Caveat Emptor.  File: gawk.info, Node: Language History, Next: Gawk Summary, Prev: Sample Programs, Up: Top The Evolution of the `awk' Language *********************************** This Info file describes the GNU implementation of `awk', which follows the POSIX specification. Many `awk' users are only familiar with the original `awk' implementation in Version 7 Unix. (This implementation was the basis for `awk' in Berkeley Unix, through 4.3-Reno. The 4.4 release of Berkeley Unix uses `gawk' 2.15.2 for its version of `awk'.) This chapter briefly describes the evolution of the `awk' language, with cross references to other parts of the Info file where you can find more information. * Menu: * V7/SVR3.1:: The major changes between V7 and System V Release 3.1. * SVR4:: Minor changes between System V Releases 3.1 and 4. * POSIX:: New features from the POSIX standard. * BTL:: New features from the Bell Laboratories version of `awk'. * POSIX/GNU:: The extensions in `gawk' not in POSIX `awk'.  File: gawk.info, Node: V7/SVR3.1, Next: SVR4, Prev: Language History, Up: Language History Major Changes between V7 and SVR3.1 =================================== The `awk' language evolved considerably between the release of Version 7 Unix (1978) and the new version first made generally available in System V Release 3.1 (1987). This section summarizes the changes, with cross-references to further details. * The requirement for `;' to separate rules on a line (*note `awk' Statements Versus Lines: Statements/Lines.). * User-defined functions, and the `return' statement (*note User-defined Functions: User-defined.). * The `delete' statement (*note The `delete' Statement: Delete.). * The `do'-`while' statement (*note The `do'-`while' Statement: Do Statement.). * The built-in functions `atan2', `cos', `sin', `rand' and `srand' (*note Numeric Built-in Functions: Numeric Functions.). * The built-in functions `gsub', `sub', and `match' (*note Built-in Functions for String Manipulation: String Functions.). * The built-in functions `close', and `system' (*note Built-in Functions for Input/Output: I/O Functions.). * The `ARGC', `ARGV', `FNR', `RLENGTH', `RSTART', and `SUBSEP' built-in variables (*note Built-in Variables::.). * The conditional expression using the ternary operator `?:' (*note Conditional Expressions: Conditional Exp.). * The exponentiation operator `^' (*note Arithmetic Operators: Arithmetic Ops.) and its assignment operator form `^=' (*note Assignment Expressions: Assignment Ops.). * C-compatible operator precedence, which breaks some old `awk' programs (*note Operator Precedence (How Operators Nest): Precedence.). * Regexps as the value of `FS' (*note Specifying How Fields are Separated: Field Separators.), and as the third argument to the `split' function (*note Built-in Functions for String Manipulation: String Functions.). * Dynamic regexps as operands of the `~' and `!~' operators (*note How to Use Regular Expressions: Regexp Usage.). * The escape sequences `\b', `\f', and `\r' (*note Escape Sequences::.). (Some vendors have updated their old versions of `awk' to recognize `\r', `\b', and `\f', but this is not something you can rely on.) * Redirection of input for the `getline' function (*note Explicit Input with `getline': Getline.). * Multiple `BEGIN' and `END' rules (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). * Multi-dimensional arrays (*note Multi-dimensional Arrays: Multi-dimensional.).  File: gawk.info, Node: SVR4, Next: POSIX, Prev: V7/SVR3.1, Up: Language History Changes between SVR3.1 and SVR4 =============================== The System V Release 4 version of Unix `awk' added these features (some of which originated in `gawk'): * The `ENVIRON' variable (*note Built-in Variables::.). * Multiple `-f' options on the command line (*note Command Line Options: Options.). * The `-v' option for assigning variables before program execution begins (*note Command Line Options: Options.). * The `--' option for terminating command line options. * The `\a', `\v', and `\x' escape sequences (*note Escape Sequences::.). * A defined return value for the `srand' built-in function (*note Numeric Built-in Functions: Numeric Functions.). * The `toupper' and `tolower' built-in string functions for case translation (*note Built-in Functions for String Manipulation: String Functions.). * A cleaner specification for the `%c' format-control letter in the `printf' function (*note Format-Control Letters: Control Letters.). * The ability to dynamically pass the field width and precision (`"%*.*d"') in the argument list of the `printf' function (*note Format-Control Letters: Control Letters.). * The use of regexp constants such as `/foo/' as expressions, where they are equivalent to using the matching operator, as in `$0 ~ /foo/' (*note Using Regular Expression Constants: Using Constant Regexps.).  File: gawk.info, Node: POSIX, Next: BTL, Prev: SVR4, Up: Language History Changes between SVR4 and POSIX `awk' ==================================== The POSIX Command Language and Utilities standard for `awk' introduced the following changes into the language: * The use of `-W' for implementation-specific options. * The use of `CONVFMT' for controlling the conversion of numbers to strings (*note Conversion of Strings and Numbers: Conversion.). * The concept of a numeric string, and tighter comparison rules to go with it (*note Variable Typing and Comparison Expressions: Typing and Comparison.). * More complete documentation of many of the previously undocumented features of the language. The following common extensions are not permitted by the POSIX standard: * `\x' escape sequences are not recognized (*note Escape Sequences::.). * Newlines do not act as whitespace to separate fields when `FS' is equal to a single space. * The synonym `func' for the keyword `function' is not recognized (*note Function Definition Syntax: Definition Syntax.). * The operators `**' and `**=' cannot be used in place of `^' and `^=' (*note Arithmetic Operators: Arithmetic Ops., and also *note Assignment Expressions: Assignment Ops.). * Specifying `-Ft' on the command line does not set the value of `FS' to be a single tab character (*note Specifying How Fields are Separated: Field Separators.). * The `fflush' built-in function is not supported (*note Built-in Functions for Input/Output: I/O Functions.).  File: gawk.info, Node: BTL, Next: POSIX/GNU, Prev: POSIX, Up: Language History Extensions in the Bell Laboratories `awk' ========================================= Brian Kernighan, one of the original designers of Unix `awk', has made his version available via anonymous `ftp' (*note Other Freely Available `awk' Implementations: Other Versions.). This section describes extensions in his version of `awk' that are not in POSIX `awk'. * The `-mf NNN' and `-mr NNN' command line options to set the maximum number of fields, and the maximum record size, respectively (*note Command Line Options: Options.). * The `fflush' built-in function for flushing buffered output (*note Built-in Functions for Input/Output: I/O Functions.).  File: gawk.info, Node: POSIX/GNU, Prev: BTL, Up: Language History Extensions in `gawk' Not in POSIX `awk' ======================================= The GNU implementation, `gawk', adds a number of features. This sections lists them in the order they were added to `gawk'. They can all be disabled with either the `--traditional' or `--posix' options (*note Command Line Options: Options.). Version 2.10 of `gawk' introduced these features: * The `AWKPATH' environment variable for specifying a path search for the `-f' command line option (*note Command Line Options: Options.). * The `IGNORECASE' variable and its effects (*note Case-sensitivity in Matching: Case-sensitivity.). * The `/dev/stdin', `/dev/stdout', `/dev/stderr', and `/dev/fd/N' file name interpretation (*note Special File Names in `gawk': Special Files.). Version 2.13 of `gawk' introduced these features: * The `FIELDWIDTHS' variable and its effects (*note Reading Fixed-width Data: Constant Size.). * The `systime' and `strftime' built-in functions for obtaining and printing time stamps (*note Functions for Dealing with Time Stamps: Time Functions.). * The `-W lint' option to provide source code and run time error and portability checking (*note Command Line Options: Options.). * The `-W compat' option to turn off these extensions (*note Command Line Options: Options.). * The `-W posix' option for full POSIX compliance (*note Command Line Options: Options.). Version 2.14 of `gawk' introduced these features: * The `next file' statement for skipping to the next data file (*note The `nextfile' Statement: Nextfile Statement.). Version 2.15 of `gawk' introduced these features: * The `ARGIND' variable, that tracks the movement of `FILENAME' through `ARGV' (*note Built-in Variables::.). * The `ERRNO' variable, that contains the system error message when `getline' returns -1, or when `close' fails (*note Built-in Variables::.). * The ability to use GNU-style long named options that start with `--' (*note Command Line Options: Options.). * The `--source' option for mixing command line and library file source code (*note Command Line Options: Options.). * The `/dev/pid', `/dev/ppid', `/dev/pgrpid', and `/dev/user' file name interpretation (*note Special File Names in `gawk': Special Files.). Version 3.0 of `gawk' introduced these features: * The `next file' statement became `nextfile' (*note The `nextfile' Statement: Nextfile Statement.). * The `--lint-old' option to warn about constructs that are not available in the original Version 7 Unix version of `awk' (*note Major Changes between V7 and SVR3.1: V7/SVR3.1.). * The `--traditional' option was added as a better name for `--compat' (*note Command Line Options: Options.). * The ability for `FS' to be a null string, and for the third argument to `split' to be the null string (*note Making Each Character a Separate Field: Single Character Fields.). * The ability for `RS' to be a regexp (*note How Input is Split into Records: Records.). * The `RT' variable (*note How Input is Split into Records: Records.). * The `gensub' function for more powerful text manipulation (*note Built-in Functions for String Manipulation: String Functions.). * The `strftime' function acquired a default time format, allowing it to be called with no arguments (*note Functions for Dealing with Time Stamps: Time Functions.). * Full support for both POSIX and GNU regexps (*note Regular Expressions: Regexp.). * The `--re-interval' option to provide interval expressions in regexps (*note Regular Expression Operators: Regexp Operators.). * `IGNORECASE' changed, now applying to string comparison as well as regexp operations (*note Case-sensitivity in Matching: Case-sensitivity.). * The `-m' option and the `fflush' function from the Bell Labs research version of `awk' (*note Command Line Options: Options.; also *note Built-in Functions for Input/Output: I/O Functions.). * The use of GNU Autoconf to control the configuration process (*note Compiling `gawk' for Unix: Quick Installation.). * Amiga support (*note Installing `gawk' on an Amiga: Amiga Installation.).  File: gawk.info, Node: Gawk Summary, Next: Installation, Prev: Language History, Up: Top `gawk' Summary ************** This appendix provides a brief summary of the `gawk' command line and the `awk' language. It is designed to serve as "quick reference." It is therefore terse, but complete. * Menu: * Command Line Summary:: Recapitulation of the command line. * Language Summary:: A terse review of the language. * Variables/Fields:: Variables, fields, and arrays. * Rules Summary:: Patterns and Actions, and their component parts. * Actions Summary:: Quick overview of actions. * Functions Summary:: Defining and calling functions. * Historical Features:: Some undocumented but supported "features".  File: gawk.info, Node: Command Line Summary, Next: Language Summary, Prev: Gawk Summary, Up: Gawk Summary Command Line Options Summary ============================ The command line consists of options to `gawk' itself, the `awk' program text (if not supplied via the `-f' option), and values to be made available in the `ARGC' and `ARGV' predefined `awk' variables: gawk [POSIX OR GNU STYLE OPTIONS] -f SOURCE-FILE [`--'] FILE ... gawk [POSIX OR GNU STYLE OPTIONS] [`--'] 'PROGRAM' FILE ... The options that `gawk' accepts are: `-F FS' `--field-separator FS' Use FS for the input field separator (the value of the `FS' predefined variable). `-f PROGRAM-FILE' `--file PROGRAM-FILE' Read the `awk' program source from the file PROGRAM-FILE, instead of from the first command line argument. `-mf NNN' `-mr NNN' The `f' flag sets the maximum number of fields, and the `r' flag sets the maximum record size. These options are ignored by `gawk', since `gawk' has no predefined limits; they are only for compatibility with the Bell Labs research version of Unix `awk'. `-v VAR=VAL' `--assign VAR=VAL' Assign the variable VAR the value VAL before program execution begins. `-W traditional' `-W compat' `--traditional' `--compat' Use compatibility mode, in which `gawk' extensions are turned off. `-W copyleft' `-W copyright' `--copyleft' `--copyright' Print the short version of the General Public License on the standard output, and exit. This option may disappear in a future version of `gawk'. `-W help' `-W usage' `--help' `--usage' Print a relatively short summary of the available options on the standard output, and exit. `-W lint' `--lint' Give warnings about dubious or non-portable `awk' constructs. `-W lint-old' `--lint-old' Warn about constructs that are not available in the original Version 7 Unix version of `awk'. `-W posix' `--posix' Use POSIX compatibility mode, in which `gawk' extensions are turned off and additional restrictions apply. `-W re-interval' `--re-interval' Allow interval expressions (*note Regular Expression Operators: Regexp Operators.), in regexps. `-W source=PROGRAM-TEXT' `--source PROGRAM-TEXT' Use PROGRAM-TEXT as `awk' program source code. This option allows mixing command line source code with source code from files, and is particularly useful for mixing command line programs with library functions. `-W version' `--version' Print version information for this particular copy of `gawk' on the error output. `--' Signal the end of options. This is useful to allow further arguments to the `awk' program itself to start with a `-'. This is mainly for consistency with POSIX argument parsing conventions. Any other options are flagged as invalid, but are otherwise ignored. *Note Command Line Options: Options, for more details.  File: gawk.info, Node: Language Summary, Next: Variables/Fields, Prev: Command Line Summary, Up: Gawk Summary Language Summary ================ An `awk' program consists of a sequence of zero or more pattern-action statements and optional function definitions. One or the other of the pattern and action may be omitted. PATTERN { ACTION STATEMENTS } PATTERN { ACTION STATEMENTS } function NAME(PARAMETER LIST) { ACTION STATEMENTS } `gawk' first reads the program source from the PROGRAM-FILE(s), if specified, or from the first non-option argument on the command line. The `-f' option may be used multiple times on the command line. `gawk' reads the program text from all the PROGRAM-FILE files, effectively concatenating them in the order they are specified. This is useful for building libraries of `awk' functions, without having to include them in each new `awk' program that uses them. To use a library function in a file from a program typed in on the command line, specify `--source 'PROGRAM'', and type your program in between the single quotes. *Note Command Line Options: Options. The environment variable `AWKPATH' specifies a search path to use when finding source files named with the `-f' option. The default path, which is `.:/usr/local/share/awk'(1) is used if `AWKPATH' is not set. If a file name given to the `-f' option contains a `/' character, no path search is performed. *Note The `AWKPATH' Environment Variable: AWKPATH Variable. `gawk' compiles the program into an internal form, and then proceeds to read each file named in the `ARGV' array. The initial values of `ARGV' come from the command line arguments. If there are no files named on the command line, `gawk' reads the standard input. If a "file" named on the command line has the form `VAR=VAL', it is treated as a variable assignment: the variable VAR is assigned the value VAL. If any of the files have a value that is the null string, that element in the list is skipped. For each record in the input, `gawk' tests to see if it matches any PATTERN in the `awk' program. For each pattern that the record matches, the associated ACTION is executed. ---------- Footnotes ---------- (1) The path may use a directory other than `/usr/local/share/awk', depending upon how `gawk' was built and installed.  File: gawk.info, Node: Variables/Fields, Next: Rules Summary, Prev: Language Summary, Up: Gawk Summary Variables and Fields ==================== `awk' variables are not declared; they come into existence when they are first used. Their values are either floating-point numbers or strings. `awk' also has one-dimensional arrays; multiple-dimensional arrays may be simulated. There are several predefined variables that `awk' sets as a program runs; these are summarized below. * Menu: * Fields Summary:: Input field splitting. * Built-in Summary:: `awk''s built-in variables. * Arrays Summary:: Using arrays. * Data Type Summary:: Values in `awk' are numbers or strings.  File: gawk.info, Node: Fields Summary, Next: Built-in Summary, Prev: Variables/Fields, Up: Variables/Fields Fields ------ As each input line is read, `gawk' splits the line into FIELDS, using the value of the `FS' variable as the field separator. If `FS' is a single character, fields are separated by that character. Otherwise, `FS' is expected to be a full regular expression. In the special case that `FS' is a single space, fields are separated by runs of spaces, tabs and/or newlines.(1) If `FS' is the null string (`""'), then each individual character in the record becomes a separate field. Note that the value of `IGNORECASE' (*note Case-sensitivity in Matching: Case-sensitivity.) also affects how fields are split when `FS' is a regular expression. Each field in the input line may be referenced by its position, `$1', `$2', and so on. `$0' is the whole line. The value of a field may be assigned to as well. Field numbers need not be constants: n = 5 print $n prints the fifth field in the input line. The variable `NF' is set to the total number of fields in the input line. References to non-existent fields (i.e. fields after `$NF') return the null string. However, assigning to a non-existent field (e.g., `$(NF+2) = 5') increases the value of `NF', creates any intervening fields with the null string as their value, and causes the value of `$0' to be recomputed, with the fields being separated by the value of `OFS'. Decrementing `NF' causes the values of fields past the new value to be lost, and the value of `$0' to be recomputed, with the fields being separated by the value of `OFS'. *Note Reading Input Files: Reading Files. ---------- Footnotes ---------- (1) In POSIX `awk', newline does not separate fields.  File: gawk.info, Node: Built-in Summary, Next: Arrays Summary, Prev: Fields Summary, Up: Variables/Fields Built-in Variables ------------------ `gawk''s built-in variables are: `ARGC' The number of elements in `ARGV'. See below for what is actually included in `ARGV'. `ARGIND' The index in `ARGV' of the current file being processed. When `gawk' is processing the input data files, it is always true that `FILENAME == ARGV[ARGIND]'. `ARGV' The array of command line arguments. The array is indexed from zero to `ARGC' - 1. Dynamically changing `ARGC' and the contents of `ARGV' can control the files used for data. A null-valued element in `ARGV' is ignored. `ARGV' does not include the options to `awk' or the text of the `awk' program itself. `CONVFMT' The conversion format to use when converting numbers to strings. `FIELDWIDTHS' A space separated list of numbers describing the fixed-width input data. `ENVIRON' An array of environment variable values. The array is indexed by variable name, each element being the value of that variable. Thus, the environment variable `HOME' is `ENVIRON["HOME"]'. One possible value might be `/home/arnold'. Changing this array does not affect the environment seen by programs which `gawk' spawns via redirection or the `system' function. (This may change in a future version of `gawk'.) Some operating systems do not have environment variables. The `ENVIRON' array is empty when running on these systems. `ERRNO' The system error message when an error occurs using `getline' or `close'. `FILENAME' The name of the current input file. If no files are specified on the command line, the value of `FILENAME' is the null string. `FNR' The input record number in the current input file. `FS' The input field separator, a space by default. `IGNORECASE' The case-sensitivity flag for string comparisons and regular expression operations. If `IGNORECASE' has a non-zero value, then pattern matching in rules, record separating with `RS', field splitting with `FS', regular expression matching with `~' and `!~', and the `gensub', `gsub', `index', `match', `split' and `sub' built-in functions all ignore case when doing regular expression operations, and all string comparisons are done ignoring case. The value of `IGNORECASE' does *not* affect array subscripting. `NF' The number of fields in the current input record. `NR' The total number of input records seen so far. `OFMT' The output format for numbers for the `print' statement, `"%.6g"' by default. `OFS' The output field separator, a space by default. `ORS' The output record separator, by default a newline. `RS' The input record separator, by default a newline. If `RS' is set to the null string, then records are separated by blank lines. When `RS' is set to the null string, then the newline character always acts as a field separator, in addition to whatever value `FS' may have. If `RS' is set to a multi-character string, it denotes a regexp; input text matching the regexp separates records. `RT' The input text that matched the text denoted by `RS', the record separator. `RSTART' The index of the first character last matched by `match'; zero if no match. `RLENGTH' The length of the string last matched by `match'; -1 if no match. `SUBSEP' The string used to separate multiple subscripts in array elements, by default `"\034"'. *Note Built-in Variables::, for more information.  File: gawk.info, Node: Arrays Summary, Next: Data Type Summary, Prev: Built-in Summary, Up: Variables/Fields Arrays ------ Arrays are subscripted with an expression between square brackets (`[' and `]'). Array subscripts are *always* strings; numbers are converted to strings as necessary, following the standard conversion rules (*note Conversion of Strings and Numbers: Conversion.). If you use multiple expressions separated by commas inside the square brackets, then the array subscript is a string consisting of the concatenation of the individual subscript values, converted to strings, separated by the subscript separator (the value of `SUBSEP'). The special operator `in' may be used in a conditional context to see if an array has an index consisting of a particular value. if (val in array) print array[val] If the array has multiple subscripts, use `(i, j, ...) in ARRAY' to test for existence of an element. The `in' construct may also be used in a `for' loop to iterate over all the elements of an array. *Note Scanning All Elements of an Array: Scanning an Array. You can remove an element from an array using the `delete' statement. You can clear an entire array using `delete ARRAY'. *Note Arrays in `awk': Arrays.  File: gawk.info, Node: Data Type Summary, Prev: Arrays Summary, Up: Variables/Fields Data Types ---------- The value of an `awk' expression is always either a number or a string. Some contexts (such as arithmetic operators) require numeric values. They convert strings to numbers by interpreting the text of the string as a number. If the string does not look like a number, it converts to zero. Other contexts (such as concatenation) require string values. They convert numbers to strings by effectively printing them with `sprintf'. *Note Conversion of Strings and Numbers: Conversion, for the details. To force conversion of a string value to a number, simply add zero to it. If the value you start with is already a number, this does not change it. To force conversion of a numeric value to a string, concatenate it with the null string. Comparisons are done numerically if both operands are numeric, or if one is numeric and the other is a numeric string. Otherwise one or both operands are converted to strings and a string comparison is performed. Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON' elements and the elements of an array created by `split' are the only items that can be numeric strings. String constants, such as `"3.1415927"' are not numeric strings, they are string constants. The full rules for comparisons are described in *Note Variable Typing and Comparison Expressions: Typing and Comparison. Uninitialized variables have the string value `""' (the null, or empty, string). In contexts where a number is required, this is equivalent to zero. *Note Variables::, for more information on variable naming and initialization; *note Conversion of Strings and Numbers: Conversion., for more information on how variable values are interpreted.  File: gawk.info, Node: Rules Summary, Next: Actions Summary, Prev: Variables/Fields, Up: Gawk Summary Patterns ======== * Menu: * Pattern Summary:: Quick overview of patterns. * Regexp Summary:: Quick overview of regular expressions. An `awk' program is mostly composed of rules, each consisting of a pattern followed by an action. The action is enclosed in `{' and `}'. Either the pattern may be missing, or the action may be missing, but not both. If the pattern is missing, the action is executed for every input record. A missing action is equivalent to `{ print }', which prints the entire line. Comments begin with the `#' character, and continue until the end of the line. Blank lines may be used to separate statements. Statements normally end with a newline; however, this is not the case for lines ending in a `,', `{', `?', `:', `&&', or `||'. Lines ending in `do' or `else' also have their statements automatically continued on the following line. In other cases, a line can be continued by ending it with a `\', in which case the newline is ignored. Multiple statements may be put on one line by separating each one with a `;'. This applies to both the statements within the action part of a rule (the usual case), and to the rule statements. *Note Comments in `awk' Programs: Comments, for information on `awk''s commenting convention; *note `awk' Statements Versus Lines: Statements/Lines., for a description of the line continuation mechanism in `awk'.  File: gawk.info, Node: Pattern Summary, Next: Regexp Summary, Prev: Rules Summary, Up: Rules Summary Pattern Summary --------------- `awk' patterns may be one of the following: /REGULAR EXPRESSION/ RELATIONAL EXPRESSION PATTERN && PATTERN PATTERN || PATTERN PATTERN ? PATTERN : PATTERN (PATTERN) ! PATTERN PATTERN1, PATTERN2 BEGIN END `BEGIN' and `END' are two special kinds of patterns that are not tested against the input. The action parts of all `BEGIN' rules are concatenated as if all the statements had been written in a single `BEGIN' rule. They are executed before any of the input is read. Similarly, all the `END' rules are concatenated, and executed when all the input is exhausted (or when an `exit' statement is executed). `BEGIN' and `END' patterns cannot be combined with other patterns in pattern expressions. `BEGIN' and `END' rules cannot have missing action parts. For `/REGULAR-EXPRESSION/' patterns, the associated statement is executed for each input record that matches the regular expression. Regular expressions are summarized below. A RELATIONAL EXPRESSION may use any of the operators defined below in the section on actions. These generally test whether certain fields match certain regular expressions. The `&&', `||', and `!' operators are logical "and," logical "or," and logical "not," respectively, as in C. They do short-circuit evaluation, also as in C, and are used for combining more primitive pattern expressions. As in most languages, parentheses may be used to change the order of evaluation. The `?:' operator is like the same operator in C. If the first pattern matches, then the second pattern is matched against the input record; otherwise, the third is matched. Only one of the second and third patterns is matched. The `PATTERN1, PATTERN2' form of a pattern is called a range pattern. It matches all input lines starting with a line that matches PATTERN1, and continuing until a line that matches PATTERN2, inclusive. A range pattern cannot be used as an operand of any of the pattern operators. *Note Pattern Elements: Pattern Overview.  File: gawk.info, Node: Regexp Summary, Prev: Pattern Summary, Up: Rules Summary Regular Expressions ------------------- Regular expressions are based on POSIX EREs (extended regular expressions). The escape sequences allowed in string constants are also valid in regular expressions (*note Escape Sequences::.). Regexps are composed of characters as follows: `C' matches the character C (assuming C is none of the characters listed below). `\C' matches the literal character C. `.' matches any character, *including* newline. In strict POSIX mode, `.' does not match the NUL character, which is a character with all bits equal to zero. `^' matches the beginning of a string. `$' matches the end of a string. `[ABC...]' matches any of the characters ABC... (character list). `[[:CLASS:]]' matches any character in the character class CLASS. Allowable classes are `alnum', `alpha', `blank', `cntrl', `digit', `graph', `lower', `print', `punct', `space', `upper', and `xdigit'. `[[.SYMBOL.]]' matches the multi-character collating symbol SYMBOL. `gawk' does not currently support collating symbols. `[[=CLASSNAME=]]' matches any of the equivalent characters in the current locale named by the equivalence class CLASSNAME. `gawk' does not currently support equivalence classes. `[^ABC...]' matches any character except ABC... (negated character list). `R1|R2' matches either R1 or R2 (alternation). `R1R2' matches R1, and then R2 (concatenation). `R+' matches one or more R's. `R*' matches zero or more R's. `R?' matches zero or one R's. `(R)' matches R (grouping). `R{N}' `R{N,}' `R{N,M}' matches at least N, N to any number, or N to M occurrences of R (interval expressions). `\y' matches the empty string at either the beginning or the end of a word. `\B' matches the empty string within a word. `\<' matches the empty string at the beginning of a word. `\>' matches the empty string at the end of a word. `\w' matches any word-constituent character (alphanumeric characters and the underscore). `\W' matches any character that is not word-constituent. `\`' matches the empty string at the beginning of a buffer (same as a string in `gawk'). `\'' matches the empty string at the end of a buffer. The various command line options control how `gawk' interprets characters in regexps. No options In the default case, `gawk' provide all the facilities of POSIX regexps and the GNU regexp operators described above. However, interval expressions are not supported. `--posix' Only POSIX regexps are supported, the GNU operators are not special (e.g., `\w' matches a literal `w'). Interval expressions are allowed. `--traditional' Traditional Unix `awk' regexps are matched. The GNU operators are not special, interval expressions are not available, and neither are the POSIX character classes (`[[:alnum:]]' and so on). Characters described by octal and hexadecimal escape sequences are treated literally, even if they represent regexp metacharacters. `--re-interval' Allow interval expressions in regexps, even if `--traditional' has been provided. *Note Regular Expressions: Regexp.  File: gawk.info, Node: Actions Summary, Next: Functions Summary, Prev: Rules Summary, Up: Gawk Summary Actions ======= Action statements are enclosed in braces, `{' and `}'. A missing action statement is equivalent to `{ print }'. Action statements consist of the usual assignment, conditional, and looping statements found in most languages. The operators, control statements, and Input/Output statements available are similar to those in C. Comments begin with the `#' character, and continue until the end of the line. Blank lines may be used to separate statements. Statements normally end with a newline; however, this is not the case for lines ending in a `,', `{', `?', `:', `&&', or `||'. Lines ending in `do' or `else' also have their statements automatically continued on the following line. In other cases, a line can be continued by ending it with a `\', in which case the newline is ignored. Multiple statements may be put on one line by separating each one with a `;'. This applies to both the statements within the action part of a rule (the usual case), and to the rule statements. *Note Comments in `awk' Programs: Comments, for information on `awk''s commenting convention; *note `awk' Statements Versus Lines: Statements/Lines., for a description of the line continuation mechanism in `awk'. * Menu: * Operator Summary:: `awk' operators. * Control Flow Summary:: The control statements. * I/O Summary:: The I/O statements. * Printf Summary:: A summary of `printf'. * Special File Summary:: Special file names interpreted internally. * Built-in Functions Summary:: Built-in numeric and string functions. * Time Functions Summary:: Built-in time functions. * String Constants Summary:: Escape sequences in strings.  File: gawk.info, Node: Operator Summary, Next: Control Flow Summary, Prev: Actions Summary, Up: Actions Summary Operators --------- The operators in `awk', in order of decreasing precedence, are: `(...)' Grouping. `$' Field reference. `++ --' Increment and decrement, both prefix and postfix. `^' Exponentiation (`**' may also be used, and `**=' for the assignment operator, but they are not specified in the POSIX standard). `+ - !' Unary plus, unary minus, and logical negation. `* / %' Multiplication, division, and modulus. `+ -' Addition and subtraction. `SPACE' String concatenation. `< <= > >= != ==' The usual relational operators. `~ !~' Regular expression match, negated match. `in' Array membership. `&&' Logical "and". `||' Logical "or". `?:' A conditional expression. This has the form `EXPR1 ? EXPR2 : EXPR3'. If EXPR1 is true, the value of the expression is EXPR2; otherwise it is EXPR3. Only one of EXPR2 and EXPR3 is evaluated. `= += -= *= /= %= ^=' Assignment. Both absolute assignment (`VAR=VALUE') and operator assignment (the other forms) are supported. *Note Expressions::.  File: gawk.info, Node: Control Flow Summary, Next: I/O Summary, Prev: Operator Summary, Up: Actions Summary Control Statements ------------------ The control statements are as follows: if (CONDITION) STATEMENT [ else STATEMENT ] while (CONDITION) STATEMENT do STATEMENT while (CONDITION) for (EXPR1; EXPR2; EXPR3) STATEMENT for (VAR in ARRAY) STATEMENT break continue delete ARRAY[INDEX] delete ARRAY exit [ EXPRESSION ] { STATEMENTS } *Note Control Statements in Actions: Statements.  File: gawk.info, Node: I/O Summary, Next: Printf Summary, Prev: Control Flow Summary, Up: Actions Summary I/O Statements -------------- The Input/Output statements are as follows: `getline' Set `$0' from next input record; set `NF', `NR', `FNR'. *Note Explicit Input with `getline': Getline. `getline FILE' Prints expressions to FILE. If FILE does not exist, it is created. If it does exist, its contents are deleted the first time the `print' is executed. `print EXPR-LIST >> FILE' Prints expressions to FILE. The previous contents of FILE are retained, and the output of `print' is appended to the file. `print EXPR-LIST | COMMAND' Prints expressions, sending the output down a pipe to COMMAND. The pipeline to the command stays open until the `close' function is called. `printf FMT, EXPR-LIST' Format and print. `printf FMT, EXPR-LIST > file' Format and print to FILE. If FILE does not exist, it is created. If it does exist, its contents are deleted the first time the `printf' is executed. `printf FMT, EXPR-LIST >> FILE' Format and print to FILE. The previous contents of FILE are retained, and the output of `printf' is appended to the file. `printf FMT, EXPR-LIST | COMMAND' Format and print, sending the output down a pipe to COMMAND. The pipeline to the command stays open until the `close' function is called. `getline' returns zero on end of file, and -1 on an error. In the event of an error, `getline' will set `ERRNO' to the value of a system-dependent string that describes the error.  File: gawk.info, Node: Printf Summary, Next: Special File Summary, Prev: I/O Summary, Up: Actions Summary `printf' Summary ---------------- Conversion specification have the form `%'[FLAG][WIDTH][`.'PREC]FORMAT. Items in brackets are optional. The `awk' `printf' statement and `sprintf' function accept the following conversion specification formats: `%c' An ASCII character. If the argument used for `%c' is numeric, it is treated as a character and printed. Otherwise, the argument is assumed to be a string, and the only first character of that string is printed. `%d' `%i' A decimal number (the integer part). `%e' `%E' A floating point number of the form `[-]d.dddddde[+-]dd'. The `%E' format uses `E' instead of `e'. `%f' A floating point number of the form [`-']`ddd.dddddd'. `%g' `%G' Use either the `%e' or `%f' formats, whichever produces a shorter string, with non-significant zeros suppressed. `%G' will use `%E' instead of `%e'. `%o' An unsigned octal number (again, an integer). `%s' A character string. `%x' `%X' An unsigned hexadecimal number (an integer). The `%X' format uses `A' through `F' instead of `a' through `f' for decimal 10 through 15. `%%' A single `%' character; no argument is converted. There are optional, additional parameters that may lie between the `%' and the control letter: `-' The expression should be left-justified within its field. `SPACE' For numeric conversions, prefix positive values with a space, and negative values with a minus sign. `+' The plus sign, used before the width modifier (see below), says to always supply a sign for numeric conversions, even if the data to be formatted is positive. The `+' overrides the space modifier. `#' Use an "alternate form" for certain control letters. For `o', supply a leading zero. For `x', and `X', supply a leading `0x' or `0X' for a non-zero result. For `e', `E', and `f', the result will always contain a decimal point. For `g', and `G', trailing zeros are not removed from the result. `0' A leading `0' (zero) acts as a flag, that indicates output should be padded with zeros instead of spaces. This applies even to non-numeric output formats. This flag only has an effect when the field width is wider than the value to be printed. `WIDTH' The field should be padded to this width. The field is normally padded with spaces. If the `0' flag has been used, it is padded with zeros. `.PREC' A number that specifies the precision to use when printing. For the `e', `E', and `f' formats, this specifies the number of digits you want printed to the right of the decimal point. For the `g', and `G' formats, it specifies the maximum number of significant digits. For the `d', `o', `i', `u', `x', and `X' formats, it specifies the minimum number of digits to print. For the `s' format, it specifies the maximum number of characters from the string that should be printed. Either or both of the WIDTH and PREC values may be specified as `*'. In that case, the particular value is taken from the argument list. *Note Using `printf' Statements for Fancier Printing: Printf.  File: gawk.info, Node: Special File Summary, Next: Built-in Functions Summary, Prev: Printf Summary, Up: Actions Summary Special File Names ------------------ When doing I/O redirection from either `print' or `printf' into a file, or via `getline' from a file, `gawk' recognizes certain special file names internally. These file names allow access to open file descriptors inherited from `gawk''s parent process (usually the shell). The file names are: `/dev/stdin' The standard input. `/dev/stdout' The standard output. `/dev/stderr' The standard error output. `/dev/fd/N' The file denoted by the open file descriptor N. In addition, reading the following files provides process related information about the running `gawk' program. All returned records are terminated with a newline. `/dev/pid' Returns the process ID of the current process. `/dev/ppid' Returns the parent process ID of the current process. `/dev/pgrpid' Returns the process group ID of the current process. `/dev/user' At least four space-separated fields, containing the return values of the `getuid', `geteuid', `getgid', and `getegid' system calls. If there are any additional fields, they are the group IDs returned by `getgroups' system call. (Multiple groups may not be supported on all systems.) These file names may also be used on the command line to name data files. These file names are only recognized internally if you do not actually have files with these names on your system. *Note Special File Names in `gawk': Special Files, for a longer description that provides the motivation for this feature.  File: gawk.info, Node: Built-in Functions Summary, Next: Time Functions Summary, Prev: Special File Summary, Up: Actions Summary Built-in Functions ------------------ `awk' provides a number of built-in functions for performing numeric operations, string related operations, and I/O related operations. The built-in arithmetic functions are: `atan2(Y, X)' the arctangent of Y/X in radians. `cos(EXPR)' the cosine of EXPR, which is in radians. `exp(EXPR)' the exponential function (`e ^ EXPR'). `int(EXPR)' truncates to integer. `log(EXPR)' the natural logarithm of `expr'. `rand()' a random number between zero and one. `sin(EXPR)' the sine of EXPR, which is in radians. `sqrt(EXPR)' the square root function. `srand([EXPR])' use EXPR as a new seed for the random number generator. If no EXPR is provided, the time of day is used. The return value is the previous seed for the random number generator. `awk' has the following built-in string functions: `gensub(REGEX, SUBST, HOW [, TARGET])' If HOW is a string beginning with `g' or `G', then replace each match of REGEX in TARGET with SUBST. Otherwise, replace the HOW'th occurrence. If TARGET is not supplied, use `$0'. The return value is the changed string; the original TARGET is not modified. Within SUBST, `\N', where N is a digit from one to nine, can be used to indicate the text that matched the N'th parenthesized subexpression. This function is `gawk'-specific. `gsub(REGEX, SUBST [, TARGET])' for each substring matching the regular expression REGEX in the string TARGET, substitute the string SUBST, and return the number of substitutions. If TARGET is not supplied, use `$0'. `index(STR, SEARCH)' returns the index of the string SEARCH in the string STR, or zero if SEARCH is not present. `length([STR])' returns the length of the string STR. The length of `$0' is returned if no argument is supplied. `match(STR, REGEX)' returns the position in STR where the regular expression REGEX occurs, or zero if REGEX is not present, and sets the values of `RSTART' and `RLENGTH'. `split(STR, ARR [, REGEX])' splits the string STR into the array ARR on the regular expression REGEX, and returns the number of elements. If REGEX is omitted, `FS' is used instead. REGEX can be the null string, causing each character to be placed into its own array element. The array ARR is cleared first. `sprintf(FMT, EXPR-LIST)' prints EXPR-LIST according to FMT, and returns the resulting string. `sub(REGEX, SUBST [, TARGET])' just like `gsub', but only the first matching substring is replaced. `substr(STR, INDEX [, LEN])' returns the LEN-character substring of STR starting at INDEX. If LEN is omitted, the rest of STR is used. `tolower(STR)' returns a copy of the string STR, with all the upper-case characters in STR translated to their corresponding lower-case counterparts. Non-alphabetic characters are left unchanged. `toupper(STR)' returns a copy of the string STR, with all the lower-case characters in STR translated to their corresponding upper-case counterparts. Non-alphabetic characters are left unchanged. The I/O related functions are: `close(EXPR)' Close the open file or pipe denoted by EXPR. `fflush([EXPR])' Flush any buffered output for the output file or pipe denoted by EXPR. If EXPR is omitted, standard output is flushed. If EXPR is the null string (`""'), all output buffers are flushed. `system(CMD-LINE)' Execute the command CMD-LINE, and return the exit status. If your operating system does not support `system', calling it will generate a fatal error. `system("")' can be used to force `awk' to flush any pending output. This is more portable, but less obvious, than calling `fflush'.  File: gawk.info, Node: Time Functions Summary, Next: String Constants Summary, Prev: Built-in Functions Summary, Up: Actions Summary Time Functions -------------- The following two functions are available for getting the current time of day, and for formatting time stamps. They are specific to `gawk'. `systime()' returns the current time of day as the number of seconds since a particular epoch (Midnight, January 1, 1970 UTC, on POSIX systems). `strftime([FORMAT[, TIMESTAMP]])' formats TIMESTAMP according to the specification in FORMAT. The current time of day is used if no TIMESTAMP is supplied. A default format equivalent to the output of the `date' utility is used if no FORMAT is supplied. *Note Functions for Dealing with Time Stamps: Time Functions, for the details on the conversion specifiers that `strftime' accepts.  File: gawk.info, Node: String Constants Summary, Prev: Time Functions Summary, Up: Actions Summary String Constants ---------------- String constants in `awk' are sequences of characters enclosed in double quotes (`"'). Within strings, certain "escape sequences" are recognized, as in C. These are: `\\' A literal backslash. `\a' The "alert" character; usually the ASCII BEL character. `\b' Backspace. `\f' Formfeed. `\n' Newline. `\r' Carriage return. `\t' Horizontal tab. `\v' Vertical tab. `\xHEX DIGITS' The character represented by the string of hexadecimal digits following the `\x'. As in ANSI C, all following hexadecimal digits are considered part of the escape sequence. E.g., `"\x1B"' is a string containing the ASCII ESC (escape) character. (The `\x' escape sequence is not in POSIX `awk'.) `\DDD' The character represented by the one, two, or three digit sequence of octal digits. Thus, `"\033"' is also a string containing the ASCII ESC (escape) character. `\C' The literal character C, if C is not one of the above. The escape sequences may also be used inside constant regular expressions (e.g., the regexp `/[ \t\f\n\r\v]/' matches whitespace characters). *Note Escape Sequences::.  File: gawk.info, Node: Functions Summary, Next: Historical Features, Prev: Actions Summary, Up: Gawk Summary User-defined Functions ====================== Functions in `awk' are defined as follows: function NAME(PARAMETER LIST) { STATEMENTS } Actual parameters supplied in the function call are used to instantiate the formal parameters declared in the function. Arrays are passed by reference, other variables are passed by value. If there are fewer arguments passed than there are names in PARAMETER-LIST, the extra names are given the null string as their value. Extra names have the effect of local variables. The open-parenthesis in a function call of a user-defined function must immediately follow the function name, without any intervening white space. This is to avoid a syntactic ambiguity with the concatenation operator. The word `func' may be used in place of `function' (but not in POSIX `awk'). Use the `return' statement to return a value from a function. *Note User-defined Functions: User-defined.  File: gawk.info, Node: Historical Features, Prev: Functions Summary, Up: Gawk Summary Historical Features =================== There are two features of historical `awk' implementations that `gawk' supports. First, it is possible to call the `length' built-in function not only with no arguments, but even without parentheses! a = length is the same as either of a = length() a = length($0) For example: $ echo abcdef | awk '{ print length }' -| 6 This feature is marked as "deprecated" in the POSIX standard, and `gawk' will issue a warning about its use if `--lint' is specified on the command line. (The ability to use `length' this way was actually an accident of the original Unix `awk' implementation. If any built-in function used `$0' as its default argument, it was possible to call that function without the parentheses. In particular, it was common practice to use the `length' function in this fashion, and this usage was documented in the `awk' manual page.) The other historical feature is the use of either the `break' statement, or the `continue' statement outside the body of a `while', `for', or `do' loop. Traditional `awk' implementations have treated such usage as equivalent to the `next' statement. More recent versions of Unix `awk' do not allow it. `gawk' supports this usage if `--traditional' has been specified. *Note Command Line Options: Options, for more information about the `--posix' and `--lint' options.  File: gawk.info, Node: Installation, Next: Notes, Prev: Gawk Summary, Up: Top Installing `gawk' ***************** This appendix provides instructions for installing `gawk' on the various platforms that are supported by the developers. The primary developers support Unix (and one day, GNU), while the other ports were contributed. The file `ACKNOWLEDGMENT' in the `gawk' distribution lists the electronic mail addresses of the people who did the respective ports, and they are also provided in *Note Reporting Problems and Bugs: Bugs. * Menu: * Gawk Distribution:: What is in the `gawk' distribution. * Unix Installation:: Installing `gawk' under various versions of Unix. * VMS Installation:: Installing `gawk' on VMS. * PC Installation:: Installing and Compiling `gawk' on MS-DOS and OS/2 * Atari Installation:: Installing `gawk' on the Atari ST. * Amiga Installation:: Installing `gawk' on an Amiga. * Bugs:: Reporting Problems and Bugs. * Other Versions:: Other freely available `awk' implementations.  File: gawk.info, Node: Gawk Distribution, Next: Unix Installation, Prev: Installation, Up: Installation The `gawk' Distribution ======================= This section first describes how to get the `gawk' distribution, how to extract it, and then what is in the various files and subdirectories. * Menu: * Getting:: How to get the distribution. * Extracting:: How to extract the distribution. * Distribution contents:: What is in the distribution.  File: gawk.info, Node: Getting, Next: Extracting, Prev: Gawk Distribution, Up: Gawk Distribution Getting the `gawk' Distribution ------------------------------- There are three ways you can get GNU software. 1. You can copy it from someone else who already has it. 2. You can order `gawk' directly from the Free Software Foundation. Software distributions are available for Unix, MS-DOS, and VMS, on tape and CD-ROM. The address is: Free Software Foundation 59 Temple Place--Suite 330 Boston, MA 02111-1307 USA Phone: +1-617-542-5942 Fax (including Japan): +1-617-542-2652 E-mail: `gnu@@prep.ai.mit.edu' Ordering from the FSF directly contributes to the support of the foundation and to the production of more free software. 3. You can get `gawk' by using anonymous `ftp' to the Internet host `ftp.gnu.ai.mit.edu', in the directory `/pub/gnu'. Here is a list of alternate `ftp' sites from which you can obtain GNU software. When a site is listed as "SITE`:'DIRECTORY" the DIRECTORY indicates the directory where GNU software is kept. You should use a site that is geographically close to you. Asia: `cair-archive.kaist.ac.kr:/pub/gnu' `ftp.cs.titech.ac.jp' `ftp.nectec.or.th:/pub/mirrors/gnu' `utsun.s.u-tokyo.ac.jp:/ftpsync/prep' Australia: `archie.au:/gnu' (`archie.oz' or `archie.oz.au' for ACSnet) Africa: `ftp.sun.ac.za:/pub/gnu' Middle East: `ftp.technion.ac.il:/pub/unsupported/gnu' Europe: `archive.eu.net' `ftp.denet.dk' `ftp.eunet.ch' `ftp.funet.fi:/pub/gnu' `ftp.ieunet.ie:pub/gnu' `ftp.informatik.rwth-aachen.de:/pub/gnu' `ftp.informatik.tu-muenchen.de' `ftp.luth.se:/pub/unix/gnu' `ftp.mcc.ac.uk' `ftp.stacken.kth.se' `ftp.sunet.se:/pub/gnu' `ftp.univ-lyon1.fr:pub/gnu' `ftp.win.tue.nl:/pub/gnu' `irisa.irisa.fr:/pub/gnu' `isy.liu.se' `nic.switch.ch:/mirror/gnu' `src.doc.ic.ac.uk:/gnu' `unix.hensa.ac.uk:/pub/uunet/systems/gnu' South America: `ftp.inf.utfsm.cl:/pub/gnu' `ftp.unicamp.br:/pub/gnu' Western Canada: `ftp.cs.ubc.ca:/mirror2/gnu' USA: `col.hp.com:/mirrors/gnu' `f.ms.uky.edu:/pub3/gnu' `ftp.cc.gatech.edu:/pub/gnu' `ftp.cs.columbia.edu:/archives/gnu/prep' `ftp.digex.net:/pub/gnu' `ftp.hawaii.edu:/mirrors/gnu' `ftp.kpc.com:/pub/mirror/gnu' USA (continued): `ftp.uu.net:/systems/gnu' `gatekeeper.dec.com:/pub/GNU' `jaguar.utah.edu:/gnustuff' `labrea.stanford.edu' `mrcnext.cso.uiuc.edu:/pub/gnu' `vixen.cso.uiuc.edu:/gnu' `wuarchive.wustl.edu:/systems/gnu'  File: gawk.info, Node: Extracting, Next: Distribution contents, Prev: Getting, Up: Gawk Distribution Extracting the Distribution --------------------------- `gawk' is distributed as a `tar' file compressed with the GNU Zip program, `gzip'. Once you have the distribution (for example, `gawk-3.0.3.tar.gz'), first use `gzip' to expand the file, and then use `tar' to extract it. You can use the following pipeline to produce the `gawk' distribution: # Under System V, add 'o' to the tar flags gzip -d -c gawk-3.0.3.tar.gz | tar -xvpf - This will create a directory named `gawk-3.0.3' in the current directory. The distribution file name is of the form `gawk-V.R.N.tar.gz'. The V represents the major version of `gawk', the R represents the current release of version V, and the N represents a "patch level", meaning that minor bugs have been fixed in the release. The current patch level is 3, but when retrieving distributions, you should get the version with the highest version, release, and patch level. (Note that release levels greater than or equal to 90 denote "beta," or non-production software; you may not wish to retrieve such a version unless you don't mind experimenting.) If you are not on a Unix system, you will need to make other arrangements for getting and extracting the `gawk' distribution. You should consult a local expert.  File: gawk.info, Node: Distribution contents, Prev: Extracting, Up: Gawk Distribution Contents of the `gawk' Distribution ----------------------------------- The `gawk' distribution has a number of C source files, documentation files, subdirectories and files related to the configuration process (*note Compiling and Installing `gawk' on Unix: Unix Installation.), and several subdirectories related to different, non-Unix, operating systems. various `.c', `.y', and `.h' files These files are the actual `gawk' source code. `README' `README_d/README.*' Descriptive files: `README' for `gawk' under Unix, and the rest for the various hardware and software combinations. `INSTALL' A file providing an overview of the configuration and installation process. `PORTS' A list of systems to which `gawk' has been ported, and which have successfully run the test suite. `ACKNOWLEDGMENT' A list of the people who contributed major parts of the code or documentation. `ChangeLog' A detailed list of source code changes as bugs are fixed or improvements made. `NEWS' A list of changes to `gawk' since the last release or patch. `COPYING' The GNU General Public License. `FUTURES' A brief list of features and/or changes being contemplated for future releases, with some indication of the time frame for the feature, based on its difficulty. `LIMITATIONS' A list of those factors that limit `gawk''s performance. Most of these depend on the hardware or operating system software, and are not limits in `gawk' itself. `POSIX.STD' A description of one area where the POSIX standard for `awk' is incorrect, and how `gawk' handles the problem. `PROBLEMS' A file describing known problems with the current release. `doc/awkforai.txt' A short article describing why `gawk' is a good language for AI (Artificial Intelligence) programming. `doc/README.card' `doc/ad.block' `doc/awkcard.in' `doc/cardfonts' `doc/colors' `doc/macros' `doc/no.colors' `doc/setter.outline' The `troff' source for a five-color `awk' reference card. A modern version of `troff', such as GNU Troff (`groff') is needed to produce the color version. See the file `README.card' for instructions if you have an older `troff'. `doc/gawk.1' The `troff' source for a manual page describing `gawk'. This is distributed for the convenience of Unix users. `doc/gawk.texi' The Texinfo source file for this Info file. It should be processed with TeX to produce a printed document, and with `makeinfo' to produce an Info file. `doc/gawk.info' The generated Info file for this Info file. `doc/igawk.1' The `troff' source for a manual page describing the `igawk' program presented in *Note An Easy Way to Use Library Functions: Igawk Program. `doc/Makefile.in' The input file used during the configuration process to generate the actual `Makefile' for creating the documentation. `Makefile.in' `acconfig.h' `aclocal.m4' `configh.in' `configure.in' `configure' `custom.h' `missing/*' These files and subdirectory are used when configuring `gawk' for various Unix systems. They are explained in detail in *Note Compiling and Installing `gawk' on Unix: Unix Installation. `awklib/extract.awk' `awklib/Makefile.in' The `awklib' directory contains a copy of `extract.awk' (*note Extracting Programs from Texinfo Source Files: Extract Program.), which can be used to extract the sample programs from the Texinfo source file for this Info file, and a `Makefile.in' file, which `configure' uses to generate a `Makefile'. As part of the process of building `gawk', the library functions from *Note A Library of `awk' Functions: Library Functions, and the `igawk' program from *Note An Easy Way to Use Library Functions: Igawk Program, are extracted into ready to use files. They are installed as part of the installation process. `atari/*' Files needed for building `gawk' on an Atari ST. *Note Installing `gawk' on the Atari ST: Atari Installation, for details. `pc/*' Files needed for building `gawk' under MS-DOS and OS/2. *Note MS-DOS and OS/2 Installation and Compilation: PC Installation, for details. `vms/*' Files needed for building `gawk' under VMS. *Note How to Compile and Install `gawk' on VMS: VMS Installation, for details. `test/*' A test suite for `gawk'. You can use `make check' from the top level `gawk' directory to run your version of `gawk' against the test suite. If `gawk' successfully passes `make check' then you can be confident of a successful port.  File: gawk.info, Node: Unix Installation, Next: VMS Installation, Prev: Gawk Distribution, Up: Installation Compiling and Installing `gawk' on Unix ======================================= Usually, you can compile and install `gawk' by typing only two commands. However, if you do use an unusual system, you may need to configure `gawk' for your system yourself. * Menu: * Quick Installation:: Compiling `gawk' under Unix. * Configuration Philosophy:: How it's all supposed to work.  File: gawk.info, Node: Quick Installation, Next: Configuration Philosophy, Prev: Unix Installation, Up: Unix Installation Compiling `gawk' for Unix ------------------------- After you have extracted the `gawk' distribution, `cd' to `gawk-3.0.3'. Like most GNU software, `gawk' is configured automatically for your Unix system by running the `configure' program. This program is a Bourne shell script that was generated automatically using GNU `autoconf'. (The `autoconf' software is described fully starting with *Note Introduction: (autoconf)Top.) To configure `gawk', simply run `configure': sh ./configure This produces a `Makefile' and `config.h' tailored to your system. The `config.h' file describes various facts about your system. You may wish to edit the `Makefile' to change the `CFLAGS' variable, which controls the command line options that are passed to the C compiler (such as optimization levels, or compiling for debugging). Alternatively, you can add your own values for most `make' variables, such as `CC' and `CFLAGS', on the command line when running `configure': CC=cc CFLAGS=-g sh ./configure See the file `INSTALL' in the `gawk' distribution for all the details. After you have run `configure', and possibly edited the `Makefile', type: make and shortly thereafter, you should have an executable version of `gawk'. That's all there is to it! (If these steps do not work, please send in a bug report; *note Reporting Problems and Bugs: Bugs..)  File: gawk.info, Node: Configuration Philosophy, Prev: Quick Installation, Up: Unix Installation The Configuration Process ------------------------- (This section is of interest only if you know something about using the C language and the Unix operating system.) The source code for `gawk' generally attempts to adhere to formal standards wherever possible. This means that `gawk' uses library routines that are specified by the ANSI C standard and by the POSIX operating system interface standard. When using an ANSI C compiler, function prototypes are used to help improve the compile-time checking. Many Unix systems do not support all of either the ANSI or the POSIX standards. The `missing' subdirectory in the `gawk' distribution contains replacement versions of those subroutines that are most likely to be missing. The `config.h' file that is created by the `configure' program contains definitions that describe features of the particular operating system where you are attempting to compile `gawk'. The three things described by this file are what header files are available, so that they can be correctly included, what (supposedly) standard functions are actually available in your C libraries, and other miscellaneous facts about your variant of Unix. For example, there may not be an `st_blksize' element in the `stat' structure. In this case `HAVE_ST_BLKSIZE' would be undefined. It is possible for your C compiler to lie to `configure'. It may do so by not exiting with an error when a library function is not available. To get around this, you can edit the file `custom.h'. Use an `#ifdef' that is appropriate for your system, and either `#define' any constants that `configure' should have defined but didn't, or `#undef' any constants that `configure' defined and should not have. `custom.h' is automatically included by `config.h'. It is also possible that the `configure' program generated by `autoconf' will not work on your system in some other fashion. If you do have a problem, the file `configure.in' is the input for `autoconf'. You may be able to change this file, and generate a new version of `configure' that will work on your system. *Note Reporting Problems and Bugs: Bugs, for information on how to report problems in configuring `gawk'. The same mechanism may be used to send in updates to `configure.in' and/or `custom.h'.  File: gawk.info, Node: VMS Installation, Next: PC Installation, Prev: Unix Installation, Up: Installation How to Compile and Install `gawk' on VMS ======================================== This section describes how to compile and install `gawk' under VMS. * Menu: * VMS Compilation:: How to compile `gawk' under VMS. * VMS Installation Details:: How to install `gawk' under VMS. * VMS Running:: How to run `gawk' under VMS. * VMS POSIX:: Alternate instructions for VMS POSIX.  File: gawk.info, Node: VMS Compilation, Next: VMS Installation Details, Prev: VMS Installation, Up: VMS Installation Compiling `gawk' on VMS ----------------------- To compile `gawk' under VMS, there is a `DCL' command procedure that will issue all the necessary `CC' and `LINK' commands, and there is also a `Makefile' for use with the `MMS' utility. From the source directory, use either $ @@[.VMS]VMSBUILD.COM or $ MMS/DESCRIPTION=[.VMS]DESCRIP.MMS GAWK Depending upon which C compiler you are using, follow one of the sets of instructions in this table: VAX C V3.x Use either `vmsbuild.com' or `descrip.mms' as is. These use `CC/OPTIMIZE=NOLINE', which is essential for Version 3.0. VAX C V2.x You must have Version 2.3 or 2.4; older ones won't work. Edit either `vmsbuild.com' or `descrip.mms' according to the comments in them. For `vmsbuild.com', this just entails removing two `!' delimiters. Also edit `config.h' (which is a copy of file `[.config]vms-conf.h') and comment out or delete the two lines `#define __STDC__ 0' and `#define VAXC_BUILTINS' near the end. GNU C Edit `vmsbuild.com' or `descrip.mms'; the changes are different from those for VAX C V2.x, but equally straightforward. No changes to `config.h' should be needed. DEC C Edit `vmsbuild.com' or `descrip.mms' according to their comments. No changes to `config.h' should be needed. `gawk' has been tested under VAX/VMS 5.5-1 using VAX C V3.2, GNU C 1.40 and 2.3. It should work without modifications for VMS V4.6 and up.  File: gawk.info, Node: VMS Installation Details, Next: VMS Running, Prev: VMS Compilation, Up: VMS Installation Installing `gawk' on VMS ------------------------ To install `gawk', all you need is a "foreign" command, which is a `DCL' symbol whose value begins with a dollar sign. For example: $ GAWK :== $disk1:[gnubin]GAWK (Substitute the actual location of `gawk.exe' for `$disk1:[gnubin]'.) The symbol should be placed in the `login.com' of any user who wishes to run `gawk', so that it will be defined every time the user logs on. Alternatively, the symbol may be placed in the system-wide `sylogin.com' procedure, which will allow all users to run `gawk'. Optionally, the help entry can be loaded into a VMS help library: $ LIBRARY/HELP SYS$HELP:HELPLIB [.VMS]GAWK.HLP (You may want to substitute a site-specific help library rather than the standard VMS library `HELPLIB'.) After loading the help text, $ HELP GAWK will provide information about both the `gawk' implementation and the `awk' programming language. The logical name `AWK_LIBRARY' can designate a default location for `awk' program files. For the `-f' option, if the specified filename has no device or directory path information in it, `gawk' will look in the current directory first, then in the directory specified by the translation of `AWK_LIBRARY' if the file was not found. If after searching in both directories, the file still is not found, then `gawk' appends the suffix `.awk' to the filename and the file search will be re-tried. If `AWK_LIBRARY' is not defined, that portion of the file search will fail benignly.  File: gawk.info, Node: VMS Running, Next: VMS POSIX, Prev: VMS Installation Details, Up: VMS Installation Running `gawk' on VMS --------------------- Command line parsing and quoting conventions are significantly different on VMS, so examples in this Info file or from other sources often need minor changes. They *are* minor though, and all `awk' programs should run correctly. Here are a couple of trivial tests: $ gawk -- "BEGIN {print ""Hello, World!""}" $ gawk -"W" version ! could also be -"W version" or "-W version" Note that upper-case and mixed-case text must be quoted. The VMS port of `gawk' includes a `DCL'-style interface in addition to the original shell-style interface (see the help entry for details). One side-effect of dual command line parsing is that if there is only a single parameter (as in the quoted string program above), the command becomes ambiguous. To work around this, the normally optional `--' flag is required to force Unix style rather than `DCL' parsing. If any other dash-type options (or multiple parameters such as data files to be processed) are present, there is no ambiguity and `--' can be omitted. The default search path when looking for `awk' program files specified by the `-f' option is `"SYS$DISK:[],AWK_LIBRARY:"'. The logical name `AWKPATH' can be used to override this default. The format of `AWKPATH' is a comma-separated list of directory specifications. When defining it, the value should be quoted so that it retains a single translation, and not a multi-translation `RMS' searchlist.  File: gawk.info, Node: VMS POSIX, Prev: VMS Running, Up: VMS Installation Building and Using `gawk' on VMS POSIX -------------------------------------- Ignore the instructions above, although `vms/gawk.hlp' should still be made available in a help library. The source tree should be unpacked into a container file subsystem rather than into the ordinary VMS file system. Make sure that the two scripts, `configure' and `vms/posix-cc.sh', are executable; use `chmod +x' on them if necessary. Then execute the following two commands: psx> CC=vms/posix-cc.sh configure psx> make CC=c89 gawk The first command will construct files `config.h' and `Makefile' out of templates, using a script to make the C compiler fit `configure''s expectations. The second command will compile and link `gawk' using the C compiler directly; ignore any warnings from `make' about being unable to redefine `CC'. `configure' will take a very long time to execute, but at least it provides incremental feedback as it runs. This has been tested with VAX/VMS V6.2, VMS POSIX V2.0, and DEC C V5.2. Once built, `gawk' will work like any other shell utility. Unlike the normal VMS port of `gawk', no special command line manipulation is needed in the VMS POSIX environment.  File: gawk.info, Node: PC Installation, Next: Atari Installation, Prev: VMS Installation, Up: Installation MS-DOS and OS/2 Installation and Compilation ============================================ If you have received a binary distribution prepared by the DOS maintainers, then `gawk' and the necessary support files will appear under the `gnu' directory, with executables in `gnu/bin', libraries in `gnu/lib/awk', and manual pages under `gnu/man'. This is designed for easy installation to a `/gnu' directory on your drive, but the files can be installed anywhere provided `AWKPATH' is set properly. Regardless of the installation directory, the first line of `igawk.cmd' and `igawk.bat' (in `gnu/bin') may need to be edited. The binary distribution will contain a separate file describing the contents. In particular, it may include more than one version of the `gawk' executable. OS/2 binary distributions may have a different arrangement, but installation is similar. The OS/2 and MS-DOS versions of `gawk' search for program files as described in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. However, semicolons (rather than colons) separate elements in the `AWKPATH' variable. If `AWKPATH' is not set or is empty, then the default search path is `".;c:/lib/awk;c:/gnu/lib/awk"'. An `sh'-like shell (as opposed to `command.com' under MS-DOS or `cmd.exe' under OS/2) may be useful for `awk' programming. Ian Stewartson has written an excellent shell for MS-DOS and OS/2, and a `ksh' clone and GNU Bash are available for OS/2. The file `README_d/README.pc' in the `gawk' distribution contains information on these shells. Users of Stewartson's shell on DOS should examine its documentation on handling of command-lines. In particular, the setting for `gawk' in the shell configuration may need to be changed, and the `ignoretype' option may also be of interest. `gawk' can be compiled for MS-DOS and OS/2 using the GNU development tools from DJ Delorie (DJGPP, MS-DOS-only) or Eberhard Mattes (EMX, MS-DOS and OS/2). Microsoft C can be used to build 16-bit versions for MS-DOS and OS/2. The file `README_d/README.pc' in the `gawk' distribution contains additional notes, and `pc/Makefile' contains important notes on compilation options. To build `gawk', copy the files in the `pc' directory (*except* for `ChangeLog') to the directory with the rest of the `gawk' sources. The `Makefile' contains a configuration section with comments, and may need to be edited in order to work with your `make' utility. The `Makefile' contains a number of targets for building various MS-DOS and OS/2 versions. A list of targets will be printed if the `make' command is given without a target. As an example, to build `gawk' using the DJGPP tools, enter `make djgpp'. Using `make' to run the standard tests and to install `gawk' requires additional Unix-like tools, including `sh', `sed', and `cp'. In order to run the tests, the `test/*.ok' files may need to be converted so that they have the usual DOS-style end-of-line markers. Most of the tests will work properly with Stewartson's shell along with the companion utilities or appropriate GNU utilities. However, some editing of `test/Makefile' is required. It is recommended that the file `pc/Makefile.tst' be copied to `test/Makefile' as a replacement. Details can be found in `README_d/README.pc'.  File: gawk.info, Node: Atari Installation, Next: Amiga Installation, Prev: PC Installation, Up: Installation Installing `gawk' on the Atari ST ================================= There are no substantial differences when installing `gawk' on various Atari models. Compiled `gawk' executables do not require a large amount of memory with most `awk' programs and should run on all Motorola processor based models (called further ST, even if that is not exactly right). In order to use `gawk', you need to have a shell, either text or graphics, that does not map all the characters of a command line to upper-case. Maintaining case distinction in option flags is very important (*note Command Line Options: Options.). These days this is the default, and it may only be a problem for some very old machines. If your system does not preserve the case of option flags, you will need to upgrade your tools. Support for I/O redirection is necessary to make it easy to import `awk' programs from other environments. Pipes are nice to have, but not vital. * Menu: * Atari Compiling:: Compiling `gawk' on Atari * Atari Using:: Running `gawk' on Atari  File: gawk.info, Node: Atari Compiling, Next: Atari Using, Prev: Atari Installation, Up: Atari Installation Compiling `gawk' on the Atari ST -------------------------------- A proper compilation of `gawk' sources when `sizeof(int)' differs from `sizeof(void *)' requires an ANSI C compiler. An initial port was done with `gcc'. You may actually prefer executables where `int's are four bytes wide, but the other variant works as well. You may need quite a bit of memory when trying to recompile the `gawk' sources, as some source files (`regex.c' in particular) are quite big. If you run out of memory compiling such a file, try reducing the optimization level for this particular file; this may help. With a reasonable shell (Bash will do), and in particular if you run Linux, MiNT or a similar operating system, you have a pretty good chance that the `configure' utility will succeed. Otherwise sample versions of `config.h' and `Makefile.st' are given in the `atari' subdirectory and can be edited and copied to the corresponding files in the main source directory. Even if `configure' produced something, it might be advisable to compare its results with the sample versions and possibly make adjustments. Some `gawk' source code fragments depend on a preprocessor define `atarist'. This basically assumes the TOS environment with `gcc'. Modify these sections as appropriate if they are not right for your environment. Also see the remarks about `AWKPATH' and `envsep' in *Note Running `gawk' on the Atari ST: Atari Using. As shipped, the sample `config.h' claims that the `system' function is missing from the libraries, which is not true, and an alternative implementation of this function is provided in `atari/system.c'. Depending upon your particular combination of shell and operating system, you may wish to change the file to indicate that `system' is available.  File: gawk.info, Node: Atari Using, Prev: Atari Compiling, Up: Atari Installation Running `gawk' on the Atari ST ------------------------------ An executable version of `gawk' should be placed, as usual, anywhere in your `PATH' where your shell can find it. While executing, `gawk' creates a number of temporary files. When using `gcc' libraries for TOS, `gawk' looks for either of the environment variables `TEMP' or `TMPDIR', in that order. If either one is found, its value is assumed to be a directory for temporary files. This directory must exist, and if you can spare the memory, it is a good idea to put it on a RAM drive. If neither `TEMP' nor `TMPDIR' are found, then `gawk' uses the current directory for its temporary files. The ST version of `gawk' searches for its program files as described in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. The default value for the `AWKPATH' variable is taken from `DEFPATH' defined in `Makefile'. The sample `gcc'/TOS `Makefile' for the ST in the distribution sets `DEFPATH' to `".,c:\lib\awk,c:\gnu\lib\awk"'. The search path can be modified by explicitly setting `AWKPATH' to whatever you wish. Note that colons cannot be used on the ST to separate elements in the `AWKPATH' variable, since they have another, reserved, meaning. Instead, you must use a comma to separate elements in the path. When recompiling, the separating character can be modified by initializing the `envsep' variable in `atari/gawkmisc.atr' to another value. Although `awk' allows great flexibility in doing I/O redirections from within a program, this facility should be used with care on the ST running under TOS. In some circumstances the OS routines for file handle pool processing lose track of certain events, causing the computer to crash, and requiring a reboot. Often a warm reboot is sufficient. Fortunately, this happens infrequently, and in rather esoteric situations. In particular, avoid having one part of an `awk' program using `print' statements explicitly redirected to `"/dev/stdout"', while other `print' statements use the default standard output, and a calling shell has redirected standard output to a file. When `gawk' is compiled with the ST version of `gcc' and its usual libraries, it will accept both `/' and `\' as path separators. While this is convenient, it should be remembered that this removes one, technically valid, character (`/') from your file names, and that it may create problems for external programs, called via the `system' function, which may not support this convention. Whenever it is possible that a file created by `gawk' will be used by some other program, use only backslashes. Also remember that in `awk', backslashes in strings have to be doubled in order to get literal backslashes (*note Escape Sequences::.).  File: gawk.info, Node: Amiga Installation, Next: Bugs, Prev: Atari Installation, Up: Installation Installing `gawk' on an Amiga ============================= You can install `gawk' on an Amiga system using a Unix emulation environment available via anonymous `ftp' from `ftp.ninemoons.com' in the directory `pub/ade/current'. This includes a shell based on `pdksh'. The primary component of this environment is a Unix emulation library, `ixemul.lib'. A more complete distribution for the Amiga is available on the Geek Gadgets CD-ROM from: CRONUS 1840 E. Warner Road #105-265 Tempe, AZ 85284 USA US Toll Free: (800) 804-0833 Phone: +1-602-491-0442 FAX: +1-602-491-0048 Email: `info@@ninemoons.com' WWW: `http://www.ninemoons.com' Anonymous `ftp' site: `ftp.ninemoons.com' Once you have the distribution, you can configure `gawk' simply by running `configure': configure -v m68k-amigaos Then run `make', and you should be all set! (If these steps do not work, please send in a bug report; *note Reporting Problems and Bugs: Bugs..)  File: gawk.info, Node: Bugs, Next: Other Versions, Prev: Amiga Installation, Up: Installation Reporting Problems and Bugs =========================== There is nothing more dangerous than a bored archeologist. The Hitchhiker's Guide to the Galaxy If you have problems with `gawk' or think that you have found a bug, please report it to the developers; we cannot promise to do anything but we might well want to fix it. Before reporting a bug, make sure you have actually found a real bug. Carefully reread the documentation and see if it really says you can do what you're trying to do. If it's not clear whether you should be able to do something or not, report that too; it's a bug in the documentation! Before reporting a bug or trying to fix it yourself, try to isolate it to the smallest possible `awk' program and input data file that reproduces the problem. Then send us the program and data file, some idea of what kind of Unix system you're using, and the exact results `gawk' gave you. Also say what you expected to occur; this will help us decide whether the problem was really in the documentation. Once you have a precise problem, there are two e-mail addresses you can send mail to. Internet: `bug-gnu-utils@@prep.ai.mit.edu' UUCP: `uunet!prep.ai.mit.edu!bug-gnu-utils' Please include the version number of `gawk' you are using. You can get this information with the command `gawk --version'. You should send a carbon copy of your mail to Arnold Robbins, who can be reached at `arnold@@gnu.ai.mit.edu'. *Important!* Do *not* try to report bugs in `gawk' by posting to the Usenet/Internet newsgroup `comp.lang.awk'. While the `gawk' developers do occasionally read this newsgroup, there is no guarantee that we will see your posting. The steps described above are the official, recognized ways for reporting bugs. Non-bug suggestions are always welcome as well. If you have questions about things that are unclear in the documentation or are just obscure features, ask Arnold Robbins; he will try to help you out, although he may not have the time to fix the problem. You can send him electronic mail at the Internet address above. If you find bugs in one of the non-Unix ports of `gawk', please send an electronic mail message to the person who maintains that port. They are listed below, and also in the `README' file in the `gawk' distribution. Information in the `README' file should be considered authoritative if it conflicts with this Info file. The people maintaining the non-Unix ports of `gawk' are: MS-DOS Scott Deifik, `scottd@@amgen.com', and Darrel Hankerson, `hankedr@@mail.auburn.edu'. OS/2 Kai Uwe Rommel, `rommel@@ars.de'. VMS Pat Rankin, `rankin@@eql.caltech.edu'. Atari ST Michal Jaegermann, `michal@@gortel.phys.ualberta.ca'. Amiga Fred Fish, `fnf@@ninemoons.com'. If your bug is also reproducible under Unix, please send copies of your report to the general GNU bug list, as well as to Arnold Robbins, at the addresses listed above.  File: gawk.info, Node: Other Versions, Prev: Bugs, Up: Installation Other Freely Available `awk' Implementations ============================================ It's kind of fun to put comments like this in your awk code. `// Do C++ comments work? answer: yes! of course' Michael Brennan There are two other freely available `awk' implementations. This section briefly describes where to get them. Unix `awk' Brian Kernighan has been able to make his implementation of `awk' freely available. You can get it via anonymous `ftp' to the host `netlib.att.com'. Change directory to `/netlib/research'. Use "binary" or "image" mode, and retrieve `awk.bundle.Z'. This is a shell archive that has been compressed with the `compress' utility. It can be uncompressed with either `uncompress' or the GNU `gunzip' utility. This version requires an ANSI C compiler; GCC (the GNU C compiler) works quite nicely. `mawk' Michael Brennan has written an independent implementation of `awk', called `mawk'. It is available under the GPL (*note GNU GENERAL PUBLIC LICENSE: Copying.), just as `gawk' is. You can get it via anonymous `ftp' to the host `ftp.whidbey.net'. Change directory to `/pub/brennan'. Use "binary" or "image" mode, and retrieve `mawk1.3.3.tar.gz' (or the latest version that is there). `gunzip' may be used to decompress this file. Installation is similar to `gawk''s (*note Compiling and Installing `gawk' on Unix: Unix Installation.).  File: gawk.info, Node: Notes, Next: Glossary, Prev: Installation, Up: Top Implementation Notes ******************** This appendix contains information mainly of interest to implementors and maintainers of `gawk'. Everything in it applies specifically to `gawk', and not to other implementations. * Menu: * Compatibility Mode:: How to disable certain `gawk' extensions. * Additions:: Making Additions To `gawk'. * Future Extensions:: New features that may be implemented one day. * Improvements:: Suggestions for improvements by volunteers.  File: gawk.info, Node: Compatibility Mode, Next: Additions, Prev: Notes, Up: Notes Downward Compatibility and Debugging ==================================== *Note Extensions in `gawk' Not in POSIX `awk': POSIX/GNU, for a summary of the GNU extensions to the `awk' language and program. All of these features can be turned off by invoking `gawk' with the `--traditional' option, or with the `--posix' option. If `gawk' is compiled for debugging with `-DDEBUG', then there is one more option available on the command line: `-W parsedebug' `--parsedebug' Print out the parse stack information as the program is being parsed. This option is intended only for serious `gawk' developers, and not for the casual user. It probably has not even been compiled into your version of `gawk', since it slows down execution.  File: gawk.info, Node: Additions, Next: Future Extensions, Prev: Compatibility Mode, Up: Notes Making Additions to `gawk' ========================== If you should find that you wish to enhance `gawk' in a significant fashion, you are perfectly free to do so. That is the point of having free software; the source code is available, and you are free to change it as you wish (*note GNU GENERAL PUBLIC LICENSE: Copying.). This section discusses the ways you might wish to change `gawk', and any considerations you should bear in mind. * Menu: * Adding Code:: Adding code to the main body of `gawk'. * New Ports:: Porting `gawk' to a new operating system.  File: gawk.info, Node: Adding Code, Next: New Ports, Prev: Additions, Up: Additions Adding New Features ------------------- You are free to add any new features you like to `gawk'. However, if you want your changes to be incorporated into the `gawk' distribution, there are several steps that you need to take in order to make it possible for me to include to your changes. 1. Get the latest version. It is much easier for me to integrate changes if they are relative to the most recent distributed version of `gawk'. If your version of `gawk' is very old, I may not be able to integrate them at all. *Note Getting the `gawk' Distribution: Getting, for information on getting the latest version of `gawk'. 2. See *note : (Version)Top standards, GNU Coding Standards. This document describes how GNU software should be written. If you haven't read it, please do so, preferably *before* starting to modify `gawk'. (The `GNU Coding Standards' are available as part of the Autoconf distribution, from the FSF.) 3. Use the `gawk' coding style. The C code for `gawk' follows the instructions in the `GNU Coding Standards', with minor exceptions. The code is formatted using the traditional "K&R" style, particularly as regards the placement of braces and the use of tabs. In brief, the coding rules for `gawk' are: * Use old style (non-prototype) function headers when defining functions. * Put the name of the function at the beginning of its own line. * Put the return type of the function, even if it is `int', on the line above the line with the name and arguments of the function. * The declarations for the function arguments should not be indented. * Put spaces around parentheses used in control structures (`if', `while', `for', `do', `switch' and `return'). * Do not put spaces in front of parentheses used in function calls. * Put spaces around all C operators, and after commas in function calls. * Do not use the comma operator to produce multiple side-effects, except in `for' loop initialization and increment parts, and in macro bodies. * Use real tabs for indenting, not spaces. * Use the "K&R" brace layout style. * Use comparisons against `NULL' and `'\0'' in the conditions of `if', `while' and `for' statements, and in the `case's of `switch' statements, instead of just the plain pointer or character value. * Use the `TRUE', `FALSE', and `NULL' symbolic constants, and the character constant `'\0'' where appropriate, instead of `1' and `0'. * Provide one-line descriptive comments for each function. * Do not use `#elif'. Many older Unix C compilers cannot handle it. * Do not use the `alloca' function for allocating memory off the stack. Its use causes more portability trouble than the minor benefit of not having to free the storage. Instead, use `malloc' and `free'. If I have to reformat your code to follow the coding style used in `gawk', I may not bother. 4. Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your changes, you must either place those changes in the public domain, and submit a signed statement to that effect, or assign the copyright in your changes to the FSF. Both of these actions are easy to do, and *many* people have done so already. If you have questions, please contact me (*note Reporting Problems and Bugs: Bugs.), or `gnu@@prep.ai.mit.edu'. 5. Update the documentation. Along with your new code, please supply new sections and or chapters for this Info file. If at all possible, please use real Texinfo, instead of just supplying unformatted ASCII text (although even that is better than no documentation at all). Conventions to be followed in `Effective AWK Programming' are provided after the `@@bye' at the end of the Texinfo source file. If possible, please update the man page as well. You will also have to sign paperwork for your documentation changes. 6. Submit changes as context diffs or unified diffs. Use `diff -c -r -N' or `diff -u -r -N' to compare the original `gawk' source tree with your version. (I find context diffs to be more readable, but unified diffs are more compact.) I recommend using the GNU version of `diff'. Send the output produced by either run of `diff' to me when you submit your changes. *Note Reporting Problems and Bugs: Bugs, for the electronic mail information. Using this format makes it easy for me to apply your changes to the master version of the `gawk' source code (using `patch'). If I have to apply the changes manually, using a text editor, I may not do so, particularly if there are lots of changes. Although this sounds like a lot of work, please remember that while you may write the new code, I have to maintain it and support it, and if it isn't possible for me to do that with a minimum of extra work, then I probably will not.  File: gawk.info, Node: New Ports, Prev: Adding Code, Up: Additions Porting `gawk' to a New Operating System ---------------------------------------- If you wish to port `gawk' to a new operating system, there are several steps to follow. 1. Follow the guidelines in *Note Adding New Features: Adding Code, concerning coding style, submission of diffs, and so on. 2. When doing a port, bear in mind that your code must co-exist peacefully with the rest of `gawk', and the other ports. Avoid gratuitous changes to the system-independent parts of the code. If at all possible, avoid sprinkling `#ifdef's just for your port throughout the code. If the changes needed for a particular system affect too much of the code, I probably will not accept them. In such a case, you will, of course, be able to distribute your changes on your own, as long as you comply with the GPL (*note GNU GENERAL PUBLIC LICENSE: Copying.). 3. A number of the files that come with `gawk' are maintained by other people at the Free Software Foundation. Thus, you should not change them unless it is for a very good reason. I.e. changes are not out of the question, but changes to these files will be scrutinized extra carefully. The files are `alloca.c', `getopt.h', `getopt.c', `getopt1.c', `regex.h', `regex.c', `dfa.h', `dfa.c', `install-sh', and `mkinstalldirs'. 4. Be willing to continue to maintain the port. Non-Unix operating systems are supported by volunteers who maintain the code needed to compile and run `gawk' on their systems. If no-one volunteers to maintain a port, that port becomes unsupported, and it may be necessary to remove it from the distribution. 5. Supply an appropriate `gawkmisc.???' file. Each port has its own `gawkmisc.???' that implements certain operating system specific functions. This is cleaner than a plethora of `#ifdef's scattered throughout the code. The `gawkmisc.c' in the main source directory includes the appropriate `gawkmisc.???' file from each subdirectory. Be sure to update it as well. Each port's `gawkmisc.???' file has a suffix reminiscent of the machine or operating system for the port. For example, `pc/gawkmisc.pc' and `vms/gawkmisc.vms'. The use of separate suffixes, instead of plain `gawkmisc.c', makes it possible to move files from a port's subdirectory into the main subdirectory, without accidentally destroying the real `gawkmisc.c' file. (Currently, this is only an issue for the MS-DOS and OS/2 ports.) 6. Supply a `Makefile' and any other C source and header files that are necessary for your operating system. All your code should be in a separate subdirectory, with a name that is the same as, or reminiscent of, either your operating system or the computer system. If possible, try to structure things so that it is not necessary to move files out of the subdirectory into the main source directory. If that is not possible, then be sure to avoid using names for your files that duplicate the names of files in the main source directory. 7. Update the documentation. Please write a section (or sections) for this Info file describing the installation and compilation steps needed to install and/or compile `gawk' for your system. 8. Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your code, you must either place your code in the public domain, and submit a signed statement to that effect, or assign the copyright in your code to the FSF. Both of these actions are easy to do, and *many* people have done so already. If you have questions, please contact me, or `gnu@@prep.ai.mit.edu'. Following these steps will make it much easier to integrate your changes into `gawk', and have them co-exist happily with the code for other operating systems that is already there. In the code that you supply, and that you maintain, feel free to use a coding style and brace layout that suits your taste.  File: gawk.info, Node: Future Extensions, Next: Improvements, Prev: Additions, Up: Notes Probable Future Extensions ========================== AWK is a language similar to PERL, only considerably more elegant. Arnold Robbins Hey! Larry Wall This section briefly lists extensions and possible improvements that indicate the directions we are currently considering for `gawk'. The file `FUTURES' in the `gawk' distributions lists these extensions as well. This is a list of probable future changes that will be usable by the `awk' language programmer. Localization The GNU project is starting to support multiple languages. It will at least be possible to make `gawk' print its warnings and error messages in languages other than English. It may be possible for `awk' programs to also use the multiple language facilities, separate from `gawk' itself. Databases It may be possible to map a GDBM/NDBM/SDBM file into an `awk' array. A `PROCINFO' Array The special files that provide process-related information (*note Special File Names in `gawk': Special Files.) may be superseded by a `PROCINFO' array that would provide the same information, in an easier to access fashion. More `lint' warnings There are more things that could be checked for portability. Control of subprocess environment Changes made in `gawk' to the array `ENVIRON' may be propagated to subprocesses run by `gawk'. This is a list of probable improvements that will make `gawk' perform better. An Improved Version of `dfa' The `dfa' pattern matcher from GNU `grep' has some problems. Either a new version or a fixed one will deal with some important regexp matching issues. Use of GNU `malloc' The GNU version of `malloc' could potentially speed up `gawk', since it relies heavily on the use of dynamic memory allocation. Use of the `rx' regexp library The `rx' regular expression library could potentially speed up all regexp operations that require knowing the exact location of matches. This includes record termination, field and array splitting, and the `sub', `gsub', `gensub' and `match' functions.  File: gawk.info, Node: Improvements, Prev: Future Extensions, Up: Notes Suggestions for Improvements ============================ Here are some projects that would-be `gawk' hackers might like to take on. They vary in size from a few days to a few weeks of programming, depending on which one you choose and how fast a programmer you are. Please send any improvements you write to the maintainers at the GNU project. *Note Adding New Features: Adding Code, for guidelines to follow when adding new features to `gawk'. *Note Reporting Problems and Bugs: Bugs, for information on contacting the maintainers. 1. Compilation of `awk' programs: `gawk' uses a Bison (YACC-like) parser to convert the script given it into a syntax tree; the syntax tree is then executed by a simple recursive evaluator. This method incurs a lot of overhead, since the recursive evaluator performs many procedure calls to do even the simplest things. It should be possible for `gawk' to convert the script's parse tree into a C program which the user would then compile, using the normal C compiler and a special `gawk' library to provide all the needed functions (regexps, fields, associative arrays, type coercion, and so on). An easier possibility might be for an intermediate phase of `awk' to convert the parse tree into a linear byte code form like the one used in GNU Emacs Lisp. The recursive evaluator would then be replaced by a straight line byte code interpreter that would be intermediate in speed between running a compiled program and doing what `gawk' does now. 2. The programs in the test suite could use documenting in this Info file. 3. See the `FUTURES' file for more ideas. Contact us if you would seriously like to tackle any of the items listed there.  File: gawk.info, Node: Glossary, Next: Copying, Prev: Notes, Up: Top Glossary ******** Action A series of `awk' statements attached to a rule. If the rule's pattern matches an input record, `awk' executes the rule's action. Actions are always enclosed in curly braces. *Note Overview of Actions: Action Overview. Amazing `awk' Assembler Henry Spencer at the University of Toronto wrote a retargetable assembler completely as `awk' scripts. It is thousands of lines long, including machine descriptions for several eight-bit microcomputers. It is a good example of a program that would have been better written in another language. Amazingly Workable Formatter (`awf') Henry Spencer at the University of Toronto wrote a formatter that accepts a large subset of the `nroff -ms' and `nroff -man' formatting commands, using `awk' and `sh'. ANSI The American National Standards Institute. This organization produces many standards, among them the standards for the C and C++ programming languages. Assignment An `awk' expression that changes the value of some `awk' variable or data object. An object that you can assign to is called an "lvalue". The assigned values are called "rvalues". *Note Assignment Expressions: Assignment Ops. `awk' Language The language in which `awk' programs are written. `awk' Program An `awk' program consists of a series of "patterns" and "actions", collectively known as "rules". For each input record given to the program, the program's rules are all processed in turn. `awk' programs may also contain function definitions. `awk' Script Another name for an `awk' program. Bash The GNU version of the standard shell (the Bourne-Again shell). See "Bourne Shell." BBS See "Bulletin Board System." Boolean Expression Named after the English mathematician Boole. See "Logical Expression." Bourne Shell The standard shell (`/bin/sh') on Unix and Unix-like systems, originally written by Steven R. Bourne. Many shells (Bash, `ksh', `pdksh', `zsh') are generally upwardly compatible with the Bourne shell. Built-in Function The `awk' language provides built-in functions that perform various numerical, time stamp related, and string computations. Examples are `sqrt' (for the square root of a number) and `substr' (for a substring of a string). *Note Built-in Functions: Built-in. Built-in Variable `ARGC', `ARGIND', `ARGV', `CONVFMT', `ENVIRON', `ERRNO', `FIELDWIDTHS', `FILENAME', `FNR', `FS', `IGNORECASE', `NF', `NR', `OFMT', `OFS', `ORS', `RLENGTH', `RSTART', `RS', `RT', and `SUBSEP', are the variables that have special meaning to `awk'. Changing some of them affects `awk''s running environment. Several of these variables are specific to `gawk'. *Note Built-in Variables::. Braces See "Curly Braces." Bulletin Board System A computer system allowing users to log in and read and/or leave messages for other users of the system, much like leaving paper notes on a bulletin board. C The system programming language that most GNU software is written in. The `awk' programming language has C-like syntax, and this Info file points out similarities between `awk' and C when appropriate. Character Set The set of numeric codes used by a computer system to represent the characters (letters, numbers, punctuation, etc.) of a particular country or place. The most common character set in use today is ASCII (American Standard Code for Information Interchange). Many European countries use an extension of ASCII known as ISO-8859-1 (ISO Latin-1). CHEM A preprocessor for `pic' that reads descriptions of molecules and produces `pic' input for drawing them. It was written in `awk' by Brian Kernighan and Jon Bentley, and is available from `netlib@@research.att.com'. Compound Statement A series of `awk' statements, enclosed in curly braces. Compound statements may be nested. *Note Control Statements in Actions: Statements. Concatenation Concatenating two strings means sticking them together, one after another, giving a new string. For example, the string `foo' concatenated with the string `bar' gives the string `foobar'. *Note String Concatenation: Concatenation. Conditional Expression An expression using the `?:' ternary operator, such as `EXPR1 ? EXPR2 : EXPR3'. The expression EXPR1 is evaluated; if the result is true, the value of the whole expression is the value of EXPR2, otherwise the value is EXPR3. In either case, only one of EXPR2 and EXPR3 is evaluated. *Note Conditional Expressions: Conditional Exp. Comparison Expression A relation that is either true or false, such as `(a < b)'. Comparison expressions are used in `if', `while', `do', and `for' statements, and in patterns to select which input records to process. *Note Variable Typing and Comparison Expressions: Typing and Comparison. Curly Braces The characters `{' and `}'. Curly braces are used in `awk' for delimiting actions, compound statements, and function bodies. Dark Corner An area in the language where specifications often were (or still are) not clear, leading to unexpected or undesirable behavior. Such areas are marked in this Info file with "(d.c.)" in the text, and are indexed under the heading "dark corner." Data Objects These are numbers and strings of characters. Numbers are converted into strings and vice versa, as needed. *Note Conversion of Strings and Numbers: Conversion. Double Precision An internal representation of numbers that can have fractional parts. Double precision numbers keep track of more digits than do single precision numbers, but operations on them are more expensive. This is the way `awk' stores numeric values. It is the C type `double'. Dynamic Regular Expression A dynamic regular expression is a regular expression written as an ordinary expression. It could be a string constant, such as `"foo"', but it may also be an expression whose value can vary. *Note Using Dynamic Regexps: Computed Regexps. Environment A collection of strings, of the form NAME`='VAL, that each program has available to it. Users generally place values into the environment in order to provide information to various programs. Typical examples are the environment variables `HOME' and `PATH'. Empty String See "Null String." Escape Sequences A special sequence of characters used for describing non-printing characters, such as `\n' for newline, or `\033' for the ASCII ESC (escape) character. *Note Escape Sequences::. Field When `awk' reads an input record, it splits the record into pieces separated by whitespace (or by a separator regexp which you can change by setting the built-in variable `FS'). Such pieces are called fields. If the pieces are of fixed length, you can use the built-in variable `FIELDWIDTHS' to describe their lengths. *Note Specifying How Fields are Separated: Field Separators, and also see *Note Reading Fixed-width Data: Constant Size. Floating Point Number Often referred to in mathematical terms as a "rational" number, this is just a number that can have a fractional part. See "Double Precision" and "Single Precision." Format Format strings are used to control the appearance of output in the `printf' statement. Also, data conversions from numbers to strings are controlled by the format string contained in the built-in variable `CONVFMT'. *Note Format-Control Letters: Control Letters. Function A specialized group of statements used to encapsulate general or program-specific tasks. `awk' has a number of built-in functions, and also allows you to define your own. *Note Built-in Functions: Built-in, and *Note User-defined Functions: User-defined. FSF See "Free Software Foundation." Free Software Foundation A non-profit organization dedicated to the production and distribution of freely distributable software. It was founded by Richard M. Stallman, the author of the original Emacs editor. GNU Emacs is the most widely used version of Emacs today. `gawk' The GNU implementation of `awk'. General Public License This document describes the terms under which `gawk' and its source code may be distributed. (*note GNU GENERAL PUBLIC LICENSE: Copying.) GNU "GNU's not Unix". An on-going project of the Free Software Foundation to create a complete, freely distributable, POSIX-compliant computing environment. GPL See "General Public License." Hexadecimal Base 16 notation, where the digits are `0'-`9' and `A'-`F', with `A' representing 10, `B' representing 11, and so on up to `F' for 15. Hexadecimal numbers are written in C using a leading `0x', to indicate their base. Thus, `0x12' is 18 (one times 16 plus 2). I/O Abbreviation for "Input/Output," the act of moving data into and/or out of a running program. Input Record A single chunk of data read in by `awk'. Usually, an `awk' input record consists of one line of text. *Note How Input is Split into Records: Records. Integer A whole number, i.e. a number that does not have a fractional part. Keyword In the `awk' language, a keyword is a word that has special meaning. Keywords are reserved and may not be used as variable names. `gawk''s keywords are: `BEGIN', `END', `if', `else', `while', `do...while', `for', `for...in', `break', `continue', `delete', `next', `nextfile', `function', `func', and `exit'. Logical Expression An expression using the operators for logic, AND, OR, and NOT, written `&&', `||', and `!' in `awk'. Often called Boolean expressions, after the mathematician who pioneered this kind of mathematical logic. Lvalue An expression that can appear on the left side of an assignment operator. In most languages, lvalues can be variables or array elements. In `awk', a field designator can also be used as an lvalue. Null String A string with no characters in it. It is represented explicitly in `awk' programs by placing two double-quote characters next to each other (`""'). It can appear in input data by having two successive occurrences of the field separator appear next to each other. Number A numeric valued data object. The `gawk' implementation uses double precision floating point to represent numbers. Very old `awk' implementations use single precision floating point. Octal Base-eight notation, where the digits are `0'-`7'. Octal numbers are written in C using a leading `0', to indicate their base. Thus, `013' is 11 (one times 8 plus 3). Pattern Patterns tell `awk' which input records are interesting to which rules. A pattern is an arbitrary conditional expression against which input is tested. If the condition is satisfied, the pattern is said to "match" the input record. A typical pattern might compare the input record against a regular expression. *Note Pattern Elements: Pattern Overview. POSIX The name for a series of standards being developed by the IEEE that specify a Portable Operating System interface. The "IX" denotes the Unix heritage of these standards. The main standard of interest for `awk' users is `IEEE Standard for Information Technology, Standard 1003.2-1992, Portable Operating System Interface (POSIX) Part 2: Shell and Utilities'. Informally, this standard is often referred to as simply "P1003.2." Private Variables and/or functions that are meant for use exclusively by library functions, and not for the main `awk' program. Special care must be taken when naming such variables and functions. *Note Naming Library Function Global Variables: Library Names. Range (of input lines) A sequence of consecutive lines from the input file. A pattern can specify ranges of input lines for `awk' to process, or it can specify single lines. *Note Pattern Elements: Pattern Overview. Recursion When a function calls itself, either directly or indirectly. If this isn't clear, refer to the entry for "recursion." Redirection Redirection means performing input from other than the standard input stream, or output to other than the standard output stream. You can redirect the output of the `print' and `printf' statements to a file or a system command, using the `>', `>>', and `|' operators. You can redirect input to the `getline' statement using the `<' and `|' operators. *Note Redirecting Output of `print' and `printf': Redirection, and *Note Explicit Input with `getline': Getline. Regexp Short for "regular expression". A regexp is a pattern that denotes a set of strings, possibly an infinite set. For example, the regexp `R.*xp' matches any string starting with the letter `R' and ending with the letters `xp'. In `awk', regexps are used in patterns and in conditional expressions. Regexps may contain escape sequences. *Note Regular Expressions: Regexp. Regular Expression See "regexp." Regular Expression Constant A regular expression constant is a regular expression written within slashes, such as `/foo/'. This regular expression is chosen when you write the `awk' program, and cannot be changed doing its execution. *Note How to Use Regular Expressions: Regexp Usage. Rule A segment of an `awk' program that specifies how to process single input records. A rule consists of a "pattern" and an "action". `awk' reads an input record; then, for each rule, if the input record satisfies the rule's pattern, `awk' executes the rule's action. Otherwise, the rule does nothing for that input record. Rvalue A value that can appear on the right side of an assignment operator. In `awk', essentially every expression has a value. These values are rvalues. `sed' See "Stream Editor." Short-Circuit The nature of the `awk' logical operators `&&' and `||'. If the value of the entire expression can be deduced from evaluating just the left-hand side of these operators, the right-hand side will not be evaluated (*note Boolean Expressions: Boolean Ops.). Side Effect A side effect occurs when an expression has an effect aside from merely producing a value. Assignment expressions, increment and decrement expressions and function calls have side effects. *Note Assignment Expressions: Assignment Ops. Single Precision An internal representation of numbers that can have fractional parts. Single precision numbers keep track of fewer digits than do double precision numbers, but operations on them are less expensive in terms of CPU time. This is the type used by some very old versions of `awk' to store numeric values. It is the C type `float'. Space The character generated by hitting the space bar on the keyboard. Special File A file name interpreted internally by `gawk', instead of being handed directly to the underlying operating system. For example, `/dev/stderr'. *Note Special File Names in `gawk': Special Files. Stream Editor A program that reads records from an input stream and processes them one or more at a time. This is in contrast with batch programs, which may expect to read their input files in entirety before starting to do anything, and with interactive programs, which require input from the user. String A datum consisting of a sequence of characters, such as `I am a string'. Constant strings are written with double-quotes in the `awk' language, and may contain escape sequences. *Note Escape Sequences::. Tab The character generated by hitting the `TAB' key on the keyboard. It usually expands to up to eight spaces upon output. Unix A computer operating system originally developed in the early 1970's at AT&T Bell Laboratories. It initially became popular in universities around the world, and later moved into commercial evnironments as a software development system and network server system. There are many commercial versions of Unix, as well as several work-alike systems whose source code is freely available (such as Linux, NetBSD, and FreeBSD). Whitespace A sequence of space, tab, or newline characters occurring inside an input record or a string.  File: gawk.info, Node: Copying, Next: Index, Prev: Glossary, Up: Top GNU GENERAL PUBLIC LICENSE ************************** Version 2, June 1991 Copyright (C) 1989, 1991 Free Software Foundation, Inc. 59 Temple Place --- Suite 330, Boston, MA 02111-1307, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Preamble ======== The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things. To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it. For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights. We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software. Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations. Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all. The precise terms and conditions for copying, distribution and modification follow. TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The "Program", below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term "modification".) Each licensee is addressed as "you". Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does. 1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program. You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee. 2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions: a. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change. b. You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License. c. If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.) These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it. Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program. In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License. 3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following: a. Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, b. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, c. Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for non-commercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.) The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable. If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code. 4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance. 5. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it. 6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License. 7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program. If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances. It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice. This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License. 8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License. 9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation. 10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. NO WARRANTY 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. END OF TERMS AND CONDITIONS How to Apply These Terms to Your New Programs ============================================= If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES. Copyright (C) 19YY NAME OF AUTHOR This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place --- Suite 330, Boston, MA 02111-1307, USA. Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. SIGNATURE OF TY COON, 1 April 1989 Ty Coon, President of Vice This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.  File: gawk.info, Node: Index, Prev: Copying, Up: Top Index ***** * Menu: * ! operator: Boolean Ops. * != operator: Typing and Comparison. * !~ operator <1>: Regexp Constants. * !~ operator <2>: Typing and Comparison. * !~ operator <3>: Regexp Usage. * !~ operator <4>: Case-sensitivity. * !~ operator: Computed Regexps. * # (comment): Comments. * #! (executable scripts): Executable Scripts. * $ (field operator): Fields. * && operator: Boolean Ops. * --assign option: Options. * --compat option: Options. * --copyleft option: Options. * --copyright option: Options. * --field-separator option: Options. * --file option: Options. * --help option: Options. * --lint option: Options. * --lint-old option: Options. * --posix option: Options. * --source option: Options. * --traditional option: Options. * --usage option: Options. * --version option: Options. * -f option: Long. * -F option <1>: Command Line Field Separator. * -F option: Options. * -f option: Options. * -v option: Options. * -W option: Options. * /dev/fd: Special Files. * /dev/pgrpid: Special Files. * /dev/pid: Special Files. * /dev/ppid: Special Files. * /dev/stderr: Special Files. * /dev/stdin: Special Files. * /dev/stdout: Special Files. * /dev/user <1>: Special Files. * /dev/user: Passwd Functions. * < operator: Typing and Comparison. * <= operator: Typing and Comparison. * == operator: Typing and Comparison. * > operator: Typing and Comparison. * >= operator: Typing and Comparison. * \' regexp operator: GNU Regexp Operators. * \< regexp operator: GNU Regexp Operators. * \> regexp operator: GNU Regexp Operators. * \` regexp operator: GNU Regexp Operators. * \B regexp operator: GNU Regexp Operators. * \W regexp operator: GNU Regexp Operators. * \w regexp operator: GNU Regexp Operators. * \y regexp operator: GNU Regexp Operators. * _gr_init: Group Functions. * _pw_init: Passwd Functions. * _tm_addup: Mktime Function. * _tm_isleap: Mktime Function. * accessing fields: Fields. * account information <1>: Passwd Functions. * account information: Group Functions. * acronym: History. * action, curly braces: Action Overview. * action, default: Very Simple. * action, definition of: Action Overview. * action, empty: Very Simple. * action, separating statements: Action Overview. * adding new features: Adding Code. * addition: Arithmetic Ops. * Aho, Alfred: History. * AI programming, using gawk: Distribution contents. * alarm.awk: Alarm Program. * amiga: Amiga Installation. * anchors in regexps: Regexp Operators. * and operator: Boolean Ops. * anonymous ftp <1>: Getting. * anonymous ftp: Other Versions. * applications of awk: When. * ARGC: Auto-set. * ARGIND <1>: Auto-set. * ARGIND: Other Arguments. * argument processing: Getopt Function. * arguments in function call: Function Calls. * arguments, command line: Invoking Gawk. * ARGV <1>: Auto-set. * ARGV: Other Arguments. * arithmetic operators: Arithmetic Ops. * array assignment: Assigning Elements. * array reference: Reference to Elements. * Array subscripts and IGNORECASE: Array Intro. * array subscripts, uninitialized variables: Uninitialized Subscripts. * arrays: Array Intro. * arrays, associative: Array Intro. * arrays, definition of: Array Intro. * arrays, deleting an element: Delete. * arrays, deleting entire contents: Delete. * arrays, multi-dimensional subscripts: Multi-dimensional. * arrays, presence of elements: Reference to Elements. * arrays, sparse: Array Intro. * arrays, special for statement: Scanning an Array. * arrays, the in operator: Reference to Elements. * artificial intelligence, using gawk: Distribution contents. * ASCII: Ordinal Functions. * assert: Assert Function. * assert, C version: Assert Function. * assertions: Assert Function. * assignment operators: Assignment Ops. * assignment to fields: Changing Fields. * associative arrays: Array Intro. * atan2: Numeric Functions. * atari: Atari Installation. * automatic initialization: More Complex. * awk language, POSIX version <1>: OFMT. * awk language, POSIX version <2>: Next Statement. * awk language, POSIX version <3>: Continue Statement. * awk language, POSIX version <4>: Format Modifiers. * awk language, POSIX version <5>: Field Splitting Summary. * awk language, POSIX version <6>: Arithmetic Ops. * awk language, POSIX version <7>: User-modified. * awk language, POSIX version <8>: Precedence. * awk language, POSIX version <9>: Assignment Ops. * awk language, POSIX version <10>: String Functions. * awk language, POSIX version <11>: Regexp Operators. * awk language, POSIX version <12>: Escape Sequences. * awk language, POSIX version <13>: Regexp Operators. * awk language, POSIX version <14>: String Functions. * awk language, POSIX version <15>: Definition Syntax. * awk language, POSIX version <16>: Break Statement. * awk language, POSIX version <17>: Regexp Operators. * awk language, POSIX version: Conversion. * awk language, V.4 version <1>: SVR4. * awk language, V.4 version: Escape Sequences. * AWKPATH environment variable: AWKPATH Variable. * awksed: Simple Sed. * backslash continuation <1>: Statements/Lines. * backslash continuation: Egrep Program. * backslash continuation and comments: Statements/Lines. * backslash continuation in csh <1>: More Complex. * backslash continuation in csh: Statements/Lines. * basic function of awk: Getting Started. * BBS-list file: Sample Data Files. * BEGIN special pattern: BEGIN/END. * beginfile: Filetrans Function. * body of a loop: While Statement. * book, using this: This Manual. * boolean expressions: Boolean Ops. * boolean operators: Boolean Ops. * break statement: Break Statement. * break, outside of loops: Break Statement. * Brennan, Michael <1>: Other Versions. * Brennan, Michael <2>: Delete. * Brennan, Michael <3>: Other Versions. * Brennan, Michael: Simple Sed. * buffer matching operators: GNU Regexp Operators. * buffering output: I/O Functions. * buffering, interactive vs. non-interactive: I/O Functions. * buffering, non-interactive vs. interactive: I/O Functions. * buffers, flushing: I/O Functions. * bugs, known in gawk: Known Bugs. * built-in functions: Built-in. * built-in variables: Built-in Variables. * built-in variables, convey information: Auto-set. * built-in variables, user modifiable: User-modified. * call by reference: Function Caveats. * call by value: Function Caveats. * calling a function <1>: Function Caveats. * calling a function: Function Calls. * case conversion: String Functions. * case sensitivity: Case-sensitivity. * changing contents of a field: Changing Fields. * changing the record separator: Records. * character classes: Regexp Operators. * character encodings: Ordinal Functions. * character list: Regexp Operators. * character list, complemented: Regexp Operators. * character sets: Ordinal Functions. * chr: Ordinal Functions. * close <1>: I/O Functions. * close: Close Files And Pipes. * closing input files and pipes: Close Files And Pipes. * closing output files and pipes: Close Files And Pipes. * coding style used in gawk: Adding Code. * collating elements: Regexp Operators. * collating symbols: Regexp Operators. * command line: Invoking Gawk. * command line formats: Running gawk. * command line, setting FS on: Command Line Field Separator. * comments: Comments. * comments and backslash continuation: Statements/Lines. * common mistakes <1>: Typing and Comparison. * common mistakes <2>: Print Examples. * common mistakes <3>: Basic Field Splitting. * common mistakes: Computed Regexps. * comp.lang.awk: Bugs. * comparison expressions: Typing and Comparison. * comparisons, string vs. regexp: Typing and Comparison. * compatibility mode <1>: Options. * compatibility mode: POSIX/GNU. * complemented character list: Regexp Operators. * compound statement: Statements. * computed regular expressions: Computed Regexps. * concatenation: Concatenation. * conditional expression: Conditional Exp. * configuring gawk: Configuration Philosophy. * constants, types of: Constants. * continuation of lines: Statements/Lines. * continue statement: Continue Statement. * continue, outside of loops: Continue Statement. * control statement: Statements. * conversion of case: String Functions. * conversion of strings and numbers: Conversion. * conversions, during subscripting: Numeric Array Subscripts. * converting dates to timestamps: Mktime Function. * CONVFMT <1>: Numeric Array Subscripts. * CONVFMT <2>: Conversion. * CONVFMT: User-modified. * cos: Numeric Functions. * csh, backslash continuation <1>: More Complex. * csh, backslash continuation: Statements/Lines. * curly braces: Action Overview. * custom.h configuration file: Configuration Philosophy. * cut utility: Cut Program. * cut.awk: Cut Program. * d.c., see "dark corner": This Manual. * dark corner <1>: Control Letters. * dark corner <2>: Continue Statement. * dark corner <3>: Using Constant Regexps. * dark corner <4>: Single Character Fields. * dark corner <5>: OFMT. * dark corner <6>: Auto-set. * dark corner <7>: Truth Values. * dark corner <8>: Field Splitting Summary. * dark corner <9>: Assignment Options. * dark corner <10>: This Manual. * dark corner <11>: Escape Sequences. * dark corner <12>: Format Modifiers. * dark corner <13>: Break Statement. * dark corner <14>: Invoking Gawk. * dark corner <15>: Plain Getline. * dark corner <16>: Using Constant Regexps. * dark corner <17>: Getline Summary. * dark corner <18>: Multiple Line. * dark corner <19>: String Functions. * dark corner <20>: Conversion. * dark corner <21>: Uninitialized Subscripts. * dark corner <22>: Auto-set. * dark corner <23>: Records. * dark corner <24>: Exit Statement. * dark corner <25>: Other Arguments. * dark corner: Using BEGIN/END. * data-driven languages: Getting Started. * dates, converting to timestamps: Mktime Function. * decrement operators: Increment Ops. * default action: Very Simple. * default pattern: Very Simple. * defining functions: Definition Syntax. * Deifik, Scott <1>: Bugs. * Deifik, Scott: Acknowledgements. * delete statement: Delete. * deleting elements of arrays: Delete. * deleting entire arrays: Delete. * deprecated features: Obsolete. * deprecated options: Obsolete. * differences between gawk and awk <1>: Records. * differences between gawk and awk <2>: Scalar Constants. * differences between gawk and awk <3>: Getline Summary. * differences between gawk and awk <4>: ARGC and ARGV. * differences between gawk and awk <5>: Calling Built-in. * differences between gawk and awk <6>: Nextfile Statement. * differences between gawk and awk <7>: AWKPATH Variable. * differences between gawk and awk <8>: Getline Intro. * differences between gawk and awk <9>: Special Files. * differences between gawk and awk <10>: Conditional Exp. * differences between gawk and awk <11>: Arithmetic Ops. * differences between gawk and awk <12>: String Functions. * differences between gawk and awk <13>: I/O And BEGIN/END. * differences between gawk and awk <14>: Redirection. * differences between gawk and awk <15>: Case-sensitivity. * differences between gawk and awk <16>: Using Constant Regexps. * differences between gawk and awk <17>: Close Files And Pipes. * differences between gawk and awk <18>: String Functions. * differences between gawk and awk <19>: Close Files And Pipes. * differences between gawk and awk <20>: Delete. * differences between gawk and awk <21>: Single Character Fields. * differences between gawk and awk: Records. * directory search: AWKPATH Variable. * division: Arithmetic Ops. * documenting awk programs <1>: Library Names. * documenting awk programs: Comments. * dupword.awk: Dupword Program. * dynamic regular expressions: Computed Regexps. * EBCDIC: Ordinal Functions. * egrep <1>: One-shot. * egrep: Regexp Operators. * egrep utility: Egrep Program. * egrep.awk: Egrep Program. * element assignment: Assigning Elements. * element of array: Reference to Elements. * empty action: Very Simple. * empty pattern: Empty. * empty program: Invoking Gawk. * empty string <1>: Truth Values. * empty string <2>: Conversion. * empty string <3>: Regexp Field Splitting. * empty string: Records. * END special pattern: BEGIN/END. * endfile: Filetrans Function. * endgrent: Group Functions. * endpwent: Passwd Functions. * ENVIRON: Auto-set. * environment variable, AWKPATH: AWKPATH Variable. * environment variable, POSIXLY_CORRECT: Options. * equivalence classes: Regexp Operators. * ERRNO <1>: Getline Intro. * ERRNO <2>: Close Files And Pipes. * ERRNO: Auto-set. * errors, common <1>: Typing and Comparison. * errors, common <2>: Computed Regexps. * errors, common <3>: Basic Field Splitting. * errors, common: Print Examples. * escape processing, sub et. al.: String Functions. * escape sequence notation: Escape Sequences. * evaluation, order of: Calling Built-in. * examining fields: Fields. * executable scripts: Executable Scripts. * exit statement: Exit Statement. * exp: Numeric Functions. * explicit input: Getline. * exponentiation: Arithmetic Ops. * expression: Expressions. * expression, assignment: Assignment Ops. * expression, boolean: Boolean Ops. * expression, comparison: Typing and Comparison. * expression, conditional: Conditional Exp. * expression, matching: Typing and Comparison. * extract.awk: Extract Program. * features, adding: Adding Code. * fflush: I/O Functions. * field operator $: Fields. * field separator, choice of: Basic Field Splitting. * field separator, FS: Basic Field Splitting. * field separator, on command line: Command Line Field Separator. * field, changing contents of: Changing Fields. * fields: Fields. * fields, separating: Basic Field Splitting. * FIELDWIDTHS: User-modified. * file descriptors: Special Files. * file, awk program: Long. * FILENAME <1>: Reading Files. * FILENAME <2>: Getline Summary. * FILENAME: Auto-set. * FILENAME, being set by getline: Getline Summary. * Fish, Fred: Bugs. * flushing buffers: I/O Functions. * FNR <1>: Auto-set. * FNR: Records. * for (x in ...): Scanning an Array. * for statement: For Statement. * format specifier: Control Letters. * format string: Basic Printf. * format, numeric output: OFMT. * formatted output: Printf. * formatted timestamps: Gettimeofday Function. * Free Software Foundation <1>: Getting. * Free Software Foundation <2>: Manual History. * Free Software Foundation: Getting. * FreeBSD: Manual History. * Friedl, Jeffrey: Acknowledgements. * FS <1>: Basic Field Splitting. * FS: User-modified. * ftp, anonymous <1>: Getting. * ftp, anonymous: Other Versions. * function call <1>: Function Calls. * function call: Function Caveats. * function definition: Definition Syntax. * function, recursive: Definition Syntax. * functions, undefined: Function Caveats. * functions, user-defined: User-defined. * gawk coding style: Adding Code. * gensub: String Functions. * getgrent: Group Functions. * getgrent, C version: Group Functions. * getgrgid: Group Functions. * getgrnam: Group Functions. * getgruser: Group Functions. * getline: Getline. * getline, return values: Getline Intro. * getline, setting FILENAME: Getline Summary. * getopt: Getopt Function. * getopt, C version: Getopt Function. * getpwent: Passwd Functions. * getpwent, C version: Passwd Functions. * getpwnam: Passwd Functions. * getpwuid: Passwd Functions. * gettimeofday: Gettimeofday Function. * getting gawk: Getting. * GNU Project: Manual History. * grcat program: Group Functions. * grcat.c: Group Functions. * group file: Group Functions. * group information: Group Functions. * gsub: String Functions. * gsub, third argument of: String Functions. * Hankerson, Darrel <1>: Bugs. * Hankerson, Darrel: Acknowledgements. * historical features <1>: Command Line Field Separator. * historical features <2>: String Functions. * historical features <3>: Break Statement. * historical features <4>: Continue Statement. * historical features: Historical Features. * history of awk: History. * histsort.awk: History Sorting. * how awk works: Two Rules. * Hughes, Phil: Acknowledgements. * I/O from BEGIN and END: I/O And BEGIN/END. * id utility: Id Program. * id.awk: Id Program. * if-else statement: If Statement. * igawk.sh: Igawk Program. * IGNORECASE <1>: User-modified. * IGNORECASE <2>: Array Intro. * IGNORECASE: Case-sensitivity. * IGNORECASE and array subscripts: Array Intro. * ignoring case: Case-sensitivity. * implementation limits <1>: Getline Summary. * implementation limits: Redirection. * in operator: Typing and Comparison. * increment operators: Increment Ops. * index: String Functions. * initialization, automatic: More Complex. * input: Reading Files. * input file, sample: Sample Data Files. * input files, skipping: Nextfile Function. * input pipeline: Getline/Pipe. * input redirection: Getline/File. * input, explicit: Getline. * input, getline command: Getline. * input, multiple line records: Multiple Line. * input, standard: Read Terminal. * installation, amiga: Amiga Installation. * installation, atari: Atari Installation. * installation, MS-DOS and OS/2: PC Installation. * installation, unix: Quick Installation. * installation, vms: VMS Installation. * int: Numeric Functions. * interaction, awk and other programs: I/O Functions. * interactive buffering vs. non-interactive: I/O Functions. * interval expressions: Regexp Operators. * inventory-shipped file: Sample Data Files. * invocation of gawk: Invoking Gawk. * ISO 8601: Time Functions. * ISO 8859-1 <1>: Case-sensitivity. * ISO 8859-1: Glossary. * ISO Latin-1 <1>: Glossary. * ISO Latin-1: Case-sensitivity. * Jaegermann, Michal <1>: Acknowledgements. * Jaegermann, Michal: Bugs. * join: Join Function. * Kernighan, Brian <1>: Concatenation. * Kernighan, Brian <2>: Acknowledgements. * Kernighan, Brian <3>: Other Versions. * Kernighan, Brian <4>: BTL. * Kernighan, Brian: History. * known bugs: Known Bugs. * labels.awk: Labels Program. * language, awk: This Manual. * language, data-driven: Getting Started. * language, procedural: Getting Started. * leftmost longest match <1>: Multiple Line. * leftmost longest match: Leftmost Longest. * length: String Functions. * limitations <1>: Redirection. * limitations: Getline Summary. * line break: Statements/Lines. * line continuation <1>: Boolean Ops. * line continuation <2>: Print Examples. * line continuation <3>: Statements/Lines. * line continuation: Conditional Exp. * Linux <1>: Manual History. * Linux: Atari Compiling. * locale, definition of: Time Functions. * log: Numeric Functions. * logical false: Truth Values. * logical operations: Boolean Ops. * logical true: Truth Values. * login information: Passwd Functions. * long options: Invoking Gawk. * loop: While Statement. * loops, exiting: Break Statement. * lvalue: Assignment Ops. * mark parity: Ordinal Functions. * match: String Functions. * matching ranges of lines: Ranges. * matching, leftmost longest <1>: Multiple Line. * matching, leftmost longest: Leftmost Longest. * mawk: Other Versions. * merging strings: Join Function. * metacharacters: Regexp Operators. * mistakes, common <1>: Basic Field Splitting. * mistakes, common <2>: Typing and Comparison. * mistakes, common <3>: Computed Regexps. * mistakes, common: Print Examples. * mktime: Mktime Function. * modifiers (in format specifiers): Format Modifiers. * multi-dimensional subscripts: Multi-dimensional. * multiple line records: Multiple Line. * multiple passes over data: Other Arguments. * multiple statements on one line: Statements/Lines. * multiplication: Arithmetic Ops. * names, use of: Definition Syntax. * namespace issues in awk: Library Names. * namespaces: Definition Syntax. * NetBSD: Manual History. * new awk: History. * new awk vs. old awk: Names. * newline: Statements/Lines. * next file statement: Nextfile Statement. * next statement: Next Statement. * next, inside a user-defined function: Next Statement. * nextfile function: Nextfile Function. * nextfile statement: Nextfile Statement. * NF <1>: Fields. * NF: Auto-set. * non-interactive buffering vs. interactive: I/O Functions. * not operator: Boolean Ops. * NR <1>: Auto-set. * NR: Records. * null string <1>: Conversion. * null string <2>: Regexp Field Splitting. * null string: Truth Values. * null string, as array subscript: Uninitialized Subscripts. * number of fields, NF: Fields. * number of records, NR, FNR: Records. * numbers, used as subscripts: Numeric Array Subscripts. * numeric character values: Ordinal Functions. * numeric constant: Scalar Constants. * numeric output format: OFMT. * numeric string: Typing and Comparison. * numeric value: Scalar Constants. * obsolete features: Obsolete. * obsolete options: Obsolete. * OFMT <1>: User-modified. * OFMT <2>: OFMT. * OFMT: Conversion. * OFS <1>: Output Separators. * OFS: User-modified. * old awk: History. * old awk vs. new awk: Names. * one-liners: One-liners. * operations, logical: Boolean Ops. * operator precedence: Precedence. * operators, arithmetic: Arithmetic Ops. * operators, assignment: Assignment Ops. * operators, boolean: Boolean Ops. * operators, decrement: Increment Ops. * operators, increment: Increment Ops. * operators, regexp matching: Regexp Usage. * operators, relational: Typing and Comparison. * operators, short-circuit: Boolean Ops. * operators, string: Concatenation. * operators, string-matching: Regexp Usage. * options, command line: Invoking Gawk. * options, long: Invoking Gawk. * or operator: Boolean Ops. * ord: Ordinal Functions. * order of evaluation: Calling Built-in. * ORS <1>: Output Separators. * ORS: User-modified. * output: Printing. * output field separator, OFS: Output Separators. * output format specifier, OFMT: OFMT. * output record separator, ORS: Output Separators. * output redirection: Redirection. * output, buffering: I/O Functions. * output, formatted: Printf. * output, piping: Redirection. * passes, multiple: Other Arguments. * password file: Passwd Functions. * path, search: AWKPATH Variable. * pattern, BEGIN: BEGIN/END. * pattern, default: Very Simple. * pattern, definition of: Patterns and Actions. * pattern, empty: Empty. * pattern, END: BEGIN/END. * pattern, range: Ranges. * pattern, regular expressions: Regexp. * patterns, types of: Kinds of Patterns. * per file initialization and clean-up: Filetrans Function. * PERL: Future Extensions. * pipeline, input: Getline/Pipe. * pipes for output: Redirection. * portability issues <1>: Delete. * portability issues <2>: Statements/Lines. * portability issues <3>: String Functions. * portability issues <4>: Close Files And Pipes. * portability issues <5>: Definition Syntax. * portability issues <6>: I/O Functions. * portability issues <7>: Portability Notes. * portability issues: Escape Sequences. * porting gawk: New Ports. * POSIX awk <1>: Assignment Ops. * POSIX awk <2>: Field Splitting Summary. * POSIX awk <3>: Format Modifiers. * POSIX awk <4>: String Functions. * POSIX awk <5>: OFMT. * POSIX awk <6>: Escape Sequences. * POSIX awk <7>: Definition Syntax. * POSIX awk <8>: Arithmetic Ops. * POSIX awk <9>: Precedence. * POSIX awk <10>: Conversion. * POSIX awk <11>: User-modified. * POSIX awk <12>: Next Statement. * POSIX awk <13>: Continue Statement. * POSIX awk <14>: Break Statement. * POSIX awk <15>: Regexp Operators. * POSIX awk <16>: String Functions. * POSIX awk <17>: Precedence. * POSIX awk: Regexp Operators. * POSIX mode: Options. * POSIXLY_CORRECT environment variable: Options. * precedence: Precedence. * precedence, regexp operators: Regexp Operators. * print statement: Print. * printf statement, syntax of: Basic Printf. * printf, format-control characters: Control Letters. * printf, modifiers: Format Modifiers. * printing: Printing. * procedural languages: Getting Started. * process information: Special Files. * processing arguments: Getopt Function. * program file: Long. * program, awk: This Manual. * program, definition of: Getting Started. * program, self contained: Executable Scripts. * programs, documenting <1>: Comments. * programs, documenting: Library Names. * pwcat program: Passwd Functions. * pwcat.c: Passwd Functions. * quotient: Arithmetic Ops. * quoting, shell <1>: Long. * quoting, shell: Read Terminal. * Rakitzis, Byron: History Sorting. * rand: Numeric Functions. * random numbers, seed of: Numeric Functions. * range pattern: Ranges. * Rankin, Pat <1>: Acknowledgements. * Rankin, Pat <2>: Bugs. * Rankin, Pat: Assignment Ops. * reading files: Reading Files. * reading files, getline command: Getline. * reading files, multiple line records: Multiple Line. * record separator, RS: Records. * record terminator, RT: Records. * record, definition of: Records. * records, multiple line: Multiple Line. * recursive function: Definition Syntax. * redirection of input: Getline/File. * redirection of output: Redirection. * reference to array: Reference to Elements. * regexp: Regexp. * regexp as expression: Typing and Comparison. * regexp comparison vs. string comparison: Typing and Comparison. * regexp constant: Regexp Usage. * regexp constants, difference between slashes and quotes: Computed Regexps. * regexp match/non-match operators <1>: Regexp Usage. * regexp match/non-match operators: Typing and Comparison. * regexp matching operators: Regexp Usage. * regexp operators: Regexp Operators. * regexp operators, GNU specific: GNU Regexp Operators. * regexp operators, precedence of: Regexp Operators. * regexp, anchors: Regexp Operators. * regexp, dynamic: Computed Regexps. * regexp, effect of command line options: GNU Regexp Operators. * regular expression: Regexp. * regular expression metacharacters: Regexp Operators. * regular expressions as field separators: Basic Field Splitting. * regular expressions as patterns: Regexp. * regular expressions as record separators: Records. * regular expressions, computed: Computed Regexps. * relational operators: Typing and Comparison. * remainder: Arithmetic Ops. * removing elements of arrays: Delete. * return statement: Return Statement. * RFC-1036: Time Functions. * RFC-822: Time Functions. * RLENGTH <1>: String Functions. * RLENGTH: Auto-set. * Robbins, Miriam: Acknowledgements. * Rommel, Kai Uwe <1>: Bugs. * Rommel, Kai Uwe: Acknowledgements. * round: Round Function. * rounding: Round Function. * RS <1>: User-modified. * RS: Records. * RSTART <1>: String Functions. * RSTART: Auto-set. * RT <1>: Records. * RT <2>: Auto-set. * RT: Multiple Line. * rule, definition of: Getting Started. * running awk programs: Running gawk. * running long programs: Long. * rvalue: Assignment Ops. * sample input file: Sample Data Files. * scanning an array: Scanning an Array. * script, definition of: Getting Started. * scripts, executable: Executable Scripts. * scripts, shell: Executable Scripts. * search path: AWKPATH Variable. * search path, for source files: AWKPATH Variable. * sed utility <1>: Simple Sed. * sed utility <2>: Igawk Program. * sed utility: Field Splitting Summary. * seed for random numbers: Numeric Functions. * self contained programs: Executable Scripts. * shell quoting <1>: Read Terminal. * shell quoting: Long. * shell scripts: Executable Scripts. * short-circuit operators: Boolean Ops. * side effect: Assignment Ops. * simple stream editor: Simple Sed. * sin: Numeric Functions. * single character fields: Single Character Fields. * single quotes, why needed: One-shot. * skipping input files: Nextfile Function. * skipping lines between markers: Ranges. * sparse arrays: Array Intro. * split: String Functions. * split utility: Split Program. * split.awk: Split Program. * sprintf: String Functions. * sqrt: Numeric Functions. * srand: Numeric Functions. * Stallman, Richard <1>: Acknowledgements. * Stallman, Richard: Manual History. * standard error output: Special Files. * standard input <1>: Special Files. * standard input <2>: Reading Files. * standard input: Read Terminal. * standard output: Special Files. * statement, compound: Statements. * stream editor: Field Splitting Summary. * stream editor, simple: Simple Sed. * strftime: Time Functions. * string comparison vs. regexp comparison: Typing and Comparison. * string constants: Constants. * string operators: Concatenation. * string-matching operators: Regexp Usage. * sub: String Functions. * sub, third argument of: String Functions. * subscripts in arrays: Multi-dimensional. * SUBSEP <1>: User-modified. * SUBSEP: Multi-dimensional. * substr: String Functions. * subtraction: Arithmetic Ops. * system: I/O Functions. * systime: Time Functions. * Tcl: Library Names. * tee utility: Tee Program. * tee.awk: Tee Program. * terminator, record: Records. * time of day: Time Functions. * timestamps: Time Functions. * timestamps, converting from dates: Mktime Function. * timestamps, formatted: Gettimeofday Function. * tolower: String Functions. * toupper: String Functions. * translate.awk: Translate Program. * Trueman, David: Acknowledgements. * truth values: Truth Values. * type conversion: Conversion. * types of variables <1>: Typing and Comparison. * types of variables: Assignment Ops. * undefined functions: Function Caveats. * undocumented features: Undocumented. * uninitialized variables, as array subscripts: Uninitialized Subscripts. * uniq utility: Uniq Program. * uniq.awk: Uniq Program. * use of comments: Comments. * user information: Passwd Functions. * user-defined functions: User-defined. * user-defined variables: Using Variables. * uses of awk: What Is Awk. * using this book: This Manual. * values of characters as numbers: Ordinal Functions. * variable shadowing: Definition Syntax. * variable typing: Typing and Comparison. * variables, user-defined: Using Variables. * Wall, Larry: Future Extensions. * wc utility: Wc Program. * wc.awk: Wc Program. * Weinberger, Peter: History. * when to use awk: When. * while statement: While Statement. * word boundaries, matching: GNU Regexp Operators. * word, regexp definition of: GNU Regexp Operators. * wordfreq.sh: Word Sorting. * || operator: Boolean Ops. * ~ operator <1>: Typing and Comparison. * ~ operator <2>: Regexp Usage. * ~ operator <3>: Case-sensitivity. * ~ operator <4>: Computed Regexps. * ~ operator: Regexp Constants.  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Mode630421 Node: Additions631264 Node: Adding Code631962 Node: New Ports637302 Node: Future Extensions641470 Node: Improvements643718 Node: Glossary645586 Node: Copying662651 Node: Index681843  End Tag Table @ 1.1 log @Initial revision @ text @@ 1.1.1.1 log @Import GNU Awk 3.0.3. @ text @@ 1.1.1.2 log @Initial import of gawk-3.1.3. Seven releases since the last import, so the ChangeLog is quite big; please refer to the NEWS file included in the import for details. Among others, this also addresses PR 23054. @ text @d1 2 a2 1 This is gawk.info, produced by makeinfo version 4.5 from gawk.texi. d4 1 a4 1 INFO-DIR-SECTION Text creation and manipulation d6 1 a6 5 * Gawk: (gawk). A text scanning and processing language. END-INFO-DIR-ENTRY INFO-DIR-SECTION Individual utilities START-INFO-DIR-ENTRY * awk: (gawk)Invoking gawk. Text scanning and processing. d9 17 a25 2 Copyright (C) 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc. d27 4 a31 18 This is Edition 3 of `GAWK: Effective AWK Programming: A User's Guide for GNU Awk', for the 3.1.3 (or later) version of the GNU implementation of AWK. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled "GNU Free Documentation License". a. "A GNU Manual" b. "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development." d33 1 a33 1 File: gawk.info, Node: Top, Next: Foreword, Up: (dir) d41 3 a43 2 Copyright (C) 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc. d45 1 d47 38 a84 19 This is Edition 3 of `GAWK: Effective AWK Programming: A User's Guide for GNU Awk', for the 3.1.3 (or later) version of the GNU implementation of AWK. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled "GNU Free Documentation License". a. "A GNU Manual" b. "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development." * Menu: d86 262 a347 382 * Foreword:: Some nice words about this Info file. * Preface:: What this Info file is about; brief history and acknowledgments. * Getting Started:: A basic introduction to using `awk'. How to run an `awk' program. Command-line syntax. * Regexp:: All about matching things using regular expressions. * Reading Files:: How to read files and manipulate fields. * Printing:: How to print using `awk'. Describes the `print' and `printf' statements. Also describes redirection of output. * Expressions:: Expressions are the basic building blocks of statements. * Patterns and Actions:: Overviews of patterns and actions. * Arrays:: The description and use of arrays. Also includes array-oriented control statements. * Functions:: Built-in and user-defined functions. * Internationalization:: Getting `gawk' to speak your language. * Advanced Features:: Stuff for advanced users, specific to `gawk'. * Invoking Gawk:: How to run `gawk'. * Library Functions:: A Library of `awk' Functions. * Sample Programs:: Many `awk' programs with complete explanations. * Language History:: The evolution of the `awk' language. * Installation:: Installing `gawk' under various operating systems. * Notes:: Notes about `gawk' extensions and possible future work. * Basic Concepts:: A very quick intoduction to programming concepts. * Glossary:: An explanation of some unfamiliar terms. * Copying:: Your right to copy and distribute `gawk'. * GNU Free Documentation License:: The license for this Info file. * Index:: Concept and Variable Index. * History:: The history of `gawk' and `awk'. * Names:: What name to use to find `awk'. * This Manual:: Using this Info file. Includes sample input files that you can use. * Conventions:: Typographical Conventions. * Manual History:: Brief history of the GNU project and this Info file. * How To Contribute:: Helping to save the world. * Acknowledgments:: Acknowledgments. * Running gawk:: How to run `gawk' programs; includes command-line syntax. * One-shot:: Running a short throwaway `awk' program. * Read Terminal:: Using no input files (input from terminal instead). * Long:: Putting permanent `awk' programs in files. * Executable Scripts:: Making self-contained `awk' programs. * Comments:: Adding documentation to `gawk' programs. * Quoting:: More discussion of shell quoting issues. * Sample Data Files:: Sample data files for use in the `awk' programs illustrated in this Info file. * Very Simple:: A very simple example. * Two Rules:: A less simple one-line example using two rules. * More Complex:: A more complex example. * Statements/Lines:: Subdividing or combining statements into lines. * Other Features:: Other Features of `awk'. * When:: When to use `gawk' and when to use other things. * Regexp Usage:: How to Use Regular Expressions. * Escape Sequences:: How to write nonprinting characters. * Regexp Operators:: Regular Expression Operators. * Character Lists:: What can go between `[...]'. * GNU Regexp Operators:: Operators specific to GNU software. * Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. * Computed Regexps:: Using Dynamic Regexps. * Locales:: How the locale affects things. * Records:: Controlling how data is split into records. * Fields:: An introduction to fields. * Nonconstant Fields:: Nonconstant Field Numbers. * Changing Fields:: Changing the Contents of a Field. * Field Separators:: The field separator and how to change it. * Regexp Field Splitting:: Using regexps as the field separator. * Single Character Fields:: Making each character a separate field. * Command Line Field Separator:: Setting `FS' from the command-line. * Field Splitting Summary:: Some final points and a summary table. * Constant Size:: Reading constant width data. * Multiple Line:: Reading multi-line records. * Getline:: Reading files under explicit program control using the `getline' function. * Plain Getline:: Using `getline' with no arguments. * Getline/Variable:: Using `getline' into a variable. * Getline/File:: Using `getline' from a file. * Getline/Variable/File:: Using `getline' into a variable from a file. * Getline/Pipe:: Using `getline' from a pipe. * Getline/Variable/Pipe:: Using `getline' into a variable from a pipe. * Getline/Coprocess:: Using `getline' from a coprocess. * Getline/Variable/Coprocess:: Using `getline' into a variable from a coprocess. * Getline Notes:: Important things to know about `getline'. * Getline Summary:: Summary of `getline' Variants. * Print:: The `print' statement. * Print Examples:: Simple examples of `print' statements. * Output Separators:: The output separators and how to change them. * OFMT:: Controlling Numeric Output With `print'. * Printf:: The `printf' statement. * Basic Printf:: Syntax of the `printf' statement. * Control Letters:: Format-control letters. * Format Modifiers:: Format-specification modifiers. * Printf Examples:: Several examples. * Redirection:: How to redirect output to multiple files and pipes. * Special Files:: File name interpretation in `gawk'. `gawk' allows access to inherited file descriptors. * Special FD:: Special files for I/O. * Special Process:: Special files for process information. * Special Network:: Special files for network communications. * Special Caveats:: Things to watch out for. * Close Files And Pipes:: Closing Input and Output Files and Pipes. * Constants:: String, numeric and regexp constants. * Scalar Constants:: Numeric and string constants. * Nondecimal-numbers:: What are octal and hex numbers. * Regexp Constants:: Regular Expression constants. * Using Constant Regexps:: When and how to use a regexp constant. * Variables:: Variables give names to values for later use. * Using Variables:: Using variables in your programs. * Assignment Options:: Setting variables on the command-line and a summary of command-line syntax. This is an advanced method of input. * Conversion:: The conversion of strings to numbers and vice versa. * Arithmetic Ops:: Arithmetic operations (`+', `-', etc.) * Concatenation:: Concatenating strings. * Assignment Ops:: Changing the value of a variable or a field. * Increment Ops:: Incrementing the numeric value of a variable. * Truth Values:: What is ``true'' and what is ``false''. * Typing and Comparison:: How variables acquire types and how this affects comparison of numbers and strings with `<', etc. * Boolean Ops:: Combining comparison expressions using boolean operators `||' (``or''), `&&' (``and'') and `!' (``not''). * Conditional Exp:: Conditional expressions select between two subexpressions under control of a third subexpression. * Function Calls:: A function call is an expression. * Precedence:: How various operators nest. * Pattern Overview:: What goes into a pattern. * Regexp Patterns:: Using regexps as patterns. * Expression Patterns:: Any expression can be used as a pattern. * Ranges:: Pairs of patterns specify record ranges. * BEGIN/END:: Specifying initialization and cleanup rules. * Using BEGIN/END:: How and why to use BEGIN/END rules. * I/O And BEGIN/END:: I/O issues in BEGIN/END rules. * Empty:: The empty pattern, which matches every record. * Using Shell Variables:: How to use shell variables with `awk'. * Action Overview:: What goes into an action. * Statements:: Describes the various control statements in detail. * If Statement:: Conditionally execute some `awk' statements. * While Statement:: Loop until some condition is satisfied. * Do Statement:: Do specified action while looping until some condition is satisfied. * For Statement:: Another looping statement, that provides initialization and increment clauses. * Switch Statement:: Switch/case evaluation for conditional execution of statements based on a value. * Break Statement:: Immediately exit the innermost enclosing loop. * Continue Statement:: Skip to the end of the innermost enclosing loop. * Next Statement:: Stop processing the current input record. * Nextfile Statement:: Stop processing the current file. * Exit Statement:: Stop execution of `awk'. * Built-in Variables:: Summarizes the built-in variables. * User-modified:: Built-in variables that you change to control `awk'. * Auto-set:: Built-in variables where `awk' gives you information. * ARGC and ARGV:: Ways to use `ARGC' and `ARGV'. * Array Intro:: Introduction to Arrays * Reference to Elements:: How to examine one element of an array. * Assigning Elements:: How to change an element of an array. * Array Example:: Basic Example of an Array * Scanning an Array:: A variation of the `for' statement. It loops through the indices of an array's existing elements. * Delete:: The `delete' statement removes an element from an array. * Numeric Array Subscripts:: How to use numbers as subscripts in `awk'. * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. * Multi-dimensional:: Emulating multidimensional arrays in `awk'. * Multi-scanning:: Scanning multidimensional arrays. * Array Sorting:: Sorting array values and indices. * Built-in:: Summarizes the built-in functions. * Calling Built-in:: How to call built-in functions. * Numeric Functions:: Functions that work with numbers, including `int', `sin' and `rand'. * String Functions:: Functions for string manipulation, such as `split', `match' and `sprintf'. * Gory Details:: More than you want to know about `\' and `&' with `sub', `gsub', and `gensub'. * I/O Functions:: Functions for files and shell commands. * Time Functions:: Functions for dealing with timestamps. * Bitwise Functions:: Functions for bitwise operations. * I18N Functions:: Functions for string translation. * User-defined:: Describes User-defined functions in detail. * Definition Syntax:: How to write definitions and what they mean. * Function Example:: An example function definition and what it does. * Function Caveats:: Things to watch out for. * Return Statement:: Specifying the value a function returns. * Dynamic Typing:: How variable types can change at runtime. * I18N and L10N:: Internationalization and Localization. * Explaining gettext:: How GNU `gettext' works. * Programmer i18n:: Features for the programmer. * Translator i18n:: Features for the translator. * String Extraction:: Extracting marked strings. * Printf Ordering:: Rearranging `printf' arguments. * I18N Portability:: `awk'-level portability issues. * I18N Example:: A simple i18n example. * Gawk I18N:: `gawk' is also internationalized. * Nondecimal Data:: Allowing nondecimal input data. * Two-way I/O:: Two-way communications with another process. * TCP/IP Networking:: Using `gawk' for network programming. * Portal Files:: Using `gawk' with BSD portals. * Profiling:: Profiling your `awk' programs. * Command Line:: How to run `awk'. * Options:: Command-line options and their meanings. * Other Arguments:: Input file names and variable assignments. * AWKPATH Variable:: Searching directories for `awk' programs. * Obsolete:: Obsolete Options and/or features. * Undocumented:: Undocumented Options and Features. * Known Bugs:: Known Bugs in `gawk'. * Library Names:: How to best name private global variables in library functions. * General Functions:: Functions that are of general use. * Nextfile Function:: Two implementations of a `nextfile' function. * Assert Function:: A function for assertions in `awk' programs. * Round Function:: A function for rounding if `sprintf' does not do it correctly. * Cliff Random Function:: The Cliff Random Number Generator. * Ordinal Functions:: Functions for using characters as numbers and vice versa. * Join Function:: A function to join an array into a string. * Gettimeofday Function:: A function to get formatted times. * Data File Management:: Functions for managing command-line data files. * Filetrans Function:: A function for handling data file transitions. * Rewind Function:: A function for rereading the current file. * File Checking:: Checking that data files are readable. * Empty Files:: Checking for zero-length files. * Ignoring Assigns:: Treating assignments as file names. * Getopt Function:: A function for processing command-line arguments. * Passwd Functions:: Functions for getting user information. * Group Functions:: Functions for getting group information. * Running Examples:: How to run these examples. * Clones:: Clones of common utilities. * Cut Program:: The `cut' utility. * Egrep Program:: The `egrep' utility. * Id Program:: The `id' utility. * Split Program:: The `split' utility. * Tee Program:: The `tee' utility. * Uniq Program:: The `uniq' utility. * Wc Program:: The `wc' utility. * Miscellaneous Programs:: Some interesting `awk' programs. * Dupword Program:: Finding duplicated words in a document. * Alarm Program:: An alarm clock. * Translate Program:: A program similar to the `tr' utility. * Labels Program:: Printing mailing labels. * Word Sorting:: A program to produce a word usage count. * History Sorting:: Eliminating duplicate entries from a history file. * Extract Program:: Pulling out programs from Texinfo source files. * Simple Sed:: A Simple Stream Editor. * Igawk Program:: A wrapper for `awk' that includes files. * V7/SVR3.1:: The major changes between V7 and System V Release 3.1. * SVR4:: Minor changes between System V Releases 3.1 and 4. * POSIX:: New features from the POSIX standard. * BTL:: New features from the Bell Laboratories version of `awk'. * POSIX/GNU:: The extensions in `gawk' not in POSIX `awk'. * Contributors:: The major contributors to `gawk'. * Gawk Distribution:: What is in the `gawk' distribution. * Getting:: How to get the distribution. * Extracting:: How to extract the distribution. * Distribution contents:: What is in the distribution. * Unix Installation:: Installing `gawk' under various versions of Unix. * Quick Installation:: Compiling `gawk' under Unix. * Additional Configuration Options:: Other compile-time options. * Configuration Philosophy:: How it's all supposed to work. * Non-Unix Installation:: Installation on Other Operating Systems. * Amiga Installation:: Installing `gawk' on an Amiga. * BeOS Installation:: Installing `gawk' on BeOS. * PC Installation:: Installing and Compiling `gawk' on MS-DOS and OS/2. * PC Binary Installation:: Installing a prepared distribution. * PC Compiling:: Compiling `gawk' for MS-DOS, Windows32, and OS/2. * PC Using:: Running `gawk' on MS-DOS, Windows32 and OS/2. * PC Dynamic:: Compiling `gawk' for dynamic libraries. * Cygwin:: Building and running `gawk' for Cygwin. * VMS Installation:: Installing `gawk' on VMS. * VMS Compilation:: How to compile `gawk' under VMS. * VMS Installation Details:: How to install `gawk' under VMS. * VMS Running:: How to run `gawk' under VMS. * VMS POSIX:: Alternate instructions for VMS POSIX. * Unsupported:: Systems whose ports are no longer supported. * Atari Installation:: Installing `gawk' on the Atari ST. * Atari Compiling:: Compiling `gawk' on Atari. * Atari Using:: Running `gawk' on Atari. * Tandem Installation:: Installing `gawk' on a Tandem. * Bugs:: Reporting Problems and Bugs. * Other Versions:: Other freely available `awk' implementations. * Compatibility Mode:: How to disable certain `gawk' extensions. * Additions:: Making Additions To `gawk'. * Adding Code:: Adding code to the main body of `gawk'. * New Ports:: Porting `gawk' to a new operating system. * Dynamic Extensions:: Adding new built-in functions to `gawk'. * Internals:: A brief look at some `gawk' internals. * Sample Library:: A example of new functions. * Internal File Description:: What the new functions will do. * Internal File Ops:: The code for internal file operations. * Using Internal File Ops:: How to use an external extension. * Future Extensions:: New features that may be implemented one day. * Basic High Level:: The high level view. * Basic Data Typing:: A very quick intro to data types. * Floating Point Issues:: Stuff to know about floating-point numbers. a356 88 To Malka, for the new beginning.  File: gawk.info, Node: Foreword, Next: Preface, Prev: Top, Up: Top Foreword ******** Arnold Robbins and I are good friends. We were introduced 11 years ago by circumstances--and our favorite programming language, AWK. The circumstances started a couple of years earlier. I was working at a new job and noticed an unplugged Unix computer sitting in the corner. No one knew how to use it, and neither did I. However, a couple of days later it was running, and I was `root' and the one-and-only user. That day, I began the transition from statistician to Unix programmer. On one of many trips to the library or bookstore in search of books on Unix, I found the gray AWK book, a.k.a. Aho, Kernighan and Weinberger, `The AWK Programming Language', Addison-Wesley, 1988. AWK's simple programming paradigm--find a pattern in the input and then perform an action--often reduced complex or tedious data manipulations to few lines of code. I was excited to try my hand at programming in AWK. Alas, the `awk' on my computer was a limited version of the language described in the AWK book. I discovered that my computer had "old `awk'" and the AWK book described "new `awk'." I learned that this was typical; the old version refused to step aside or relinquish its name. If a system had a new `awk', it was invariably called `nawk', and few systems had it. The best way to get a new `awk' was to `ftp' the source code for `gawk' from `prep.ai.mit.edu'. `gawk' was a version of new `awk' written by David Trueman and Arnold, and available under the GNU General Public License. (Incidentally, it's no longer difficult to find a new `awk'. `gawk' ships with Linux, and you can download binaries or source code for almost any system; my wife uses `gawk' on her VMS box.) My Unix system started out unplugged from the wall; it certainly was not plugged into a network. So, oblivious to the existence of `gawk' and the Unix community in general, and desiring a new `awk', I wrote my own, called `mawk'. Before I was finished I knew about `gawk', but it was too late to stop, so I eventually posted to a `comp.sources' newsgroup. A few days after my posting, I got a friendly email from Arnold introducing himself. He suggested we share design and algorithms and attached a draft of the POSIX standard so that I could update `mawk' to support language extensions added after publication of the AWK book. Frankly, if our roles had been reversed, I would not have been so open and we probably would have never met. I'm glad we did meet. He is an AWK expert's AWK expert and a genuinely nice person. Arnold contributes significant amounts of his expertise and time to the Free Software Foundation. This book is the `gawk' reference manual, but at its core it is a book about AWK programming that will appeal to a wide audience. It is a definitive reference to the AWK language as defined by the 1987 Bell Labs release and codified in the 1992 POSIX Utilities standard. On the other hand, the novice AWK programmer can study a wealth of practical programs that emphasize the power of AWK's basic idioms: data driven control-flow, pattern matching with regular expressions, and associative arrays. Those looking for something new can try out `gawk''s interface to network protocols via special `/inet' files. The programs in this book make clear that an AWK program is typically much smaller and faster to develop than a counterpart written in C. Consequently, there is often a payoff to prototype an algorithm or design in AWK to get it running quickly and expose problems early. Often, the interpreted performance is adequate and the AWK prototype becomes the product. The new `pgawk' (profiling `gawk'), produces program execution counts. I recently experimented with an algorithm that for n lines of input, exhibited ~ C n^2 performance, while theory predicted ~ C n log n behavior. A few minutes poring over the `awkprof.out' profile pinpointed the problem to a single line of code. `pgawk' is a welcome addition to my programmer's toolbox. Arnold has distilled over a decade of experience writing and using AWK programs, and developing `gawk', into this book. If you use AWK or want to learn how, then read this book. Michael Brennan Author of `mawk' d358 1 a358 1 File: gawk.info, Node: Preface, Next: Getting Started, Prev: Foreword, Up: Top a362 37 Several kinds of tasks occur repeatedly when working with text files. You might want to extract certain lines and discard the rest. Or you may need to make changes wherever certain patterns appear, but leave the rest of the file alone. Writing single-use programs for these tasks in languages such as C, C++, or Pascal is time-consuming and inconvenient. Such jobs are often easier with `awk'. The `awk' utility interprets a special-purpose programming language that makes it easy to handle simple data-reformatting jobs. The GNU implementation of `awk' is called `gawk'; it is fully compatible with the System V Release 4 version of `awk'. `gawk' is also compatible with the POSIX specification of the `awk' language. This means that all properly written `awk' programs should work with `gawk'. Thus, we usually don't distinguish between `gawk' and other `awk' implementations. Using `awk' allows you to: * Manage small, personal databases * Generate reports * Validate data * Produce indexes and perform other document preparation tasks * Experiment with algorithms that you can adapt later to other computer languages In addition, `gawk' provides facilities that make it easy to: * Extract bits and pieces of data for processing * Sort data * Perform simple network communications d365 2 a366 2 commands, such as `cat' and `ls',(1) as well as basic shell facilities, such as input/output (I/O) redirection and pipes. d370 5 a374 6 `awk' language in general, also describes the particular implementation of `awk' called `gawk' (which stands for "GNU awk"). `gawk' runs on a broad range of Unix systems, ranging from 80386 PC-based computers up through large-scale systems, such as Crays. `gawk' has also been ported to Mac OS X, MS-DOS, Microsoft Windows (all versions) and OS/2 PCs, Atari and Amiga microcomputers, BeOS, Tandem D20, and VMS. d378 1 a378 6 * History:: The history of `gawk' and `awk'. * Names:: What name to use to find `awk'. * This Manual:: Using this Info file. Includes sample input files that you can use. * Conventions:: Typographical Conventions. d381 1 a381 2 * How To Contribute:: Helping to save the world. * Acknowledgments:: Acknowledgments. d385 2 a386 2 (1) These commands are available on POSIX-compliant systems, as well as on traditional Unix-based systems. If you are using some other d391 1 a391 1 File: gawk.info, Node: History, Next: Names, Up: Preface a395 10 Recipe For A Programming Language 1 part `egrep' 1 part `snobol' 2 parts `ed' 3 parts C Blend all parts well using `lex' and `yacc'. Document minimally and release. After eight years, add another part `egrep' and two more parts C. Document very well and release. d397 2 a398 2 Aho, Peter J. Weinberger and Brian W. Kernighan. The original version of `awk' was written in 1977 at AT&T Bell Laboratories. In 1985, a new d401 7 a407 7 expressions. This new version became widely available with Unix System V Release 3.1 (SVR3.1). The version in SVR4 added some new features and cleaned up the behavior in some of the "dark corners" of the language. The specification for `awk' in the POSIX Command Language and Utilities standard further clarified the language. Both the `gawk' designers and the original Bell Laboratories `awk' designers provided feedback for the POSIX specification. d409 2 a410 2 Paul Rubin wrote the GNU implementation, `gawk', in 1986. Jay Fenlason completed it, with advice from Richard Stallman. John Woods d412 4 a415 4 Trueman, with help from me, thoroughly reworked `gawk' for compatibility with the newer `awk'. Circa 1995, I became the primary maintainer. Current development focuses on bug fixes, performance improvements, standards compliance, and occasionally, new features. d417 2 a418 6 In May of 1997, Ju"rgen Kahrs felt the need for network access from `awk', and with a little help from me, set about adding features to do this for `gawk'. At that time, he also wrote the bulk of `TCP/IP Internetworking with `gawk'' (a separate document, available as part of the `gawk' distribution). His code finally became part of the main `gawk' distribution with `gawk' version 3.1. d420 2 a421 2 *Note Contributors::, for a complete list of those who made important contributions to `gawk'. d423 5 a427 2  File: gawk.info, Node: Names, Next: This Manual, Prev: History, Up: Preface d429 8 a436 2 A Rose by Any Other Name ======================== d438 6 a443 3 The `awk' language has evolved over the years. Full details are provided in *Note Language History::. The language described in this Info file is often referred to as "new `awk'" (`nawk'). d445 35 a479 6 Because of this, many systems have multiple versions of `awk'. Some systems have an `awk' utility that implements the original version of the `awk' language and a `nawk' utility for the new version. Others have an `oawk' version for the "old `awk'" language and plain `awk' for the new one. Still others only have one version, which is usually the new one.(1) d481 2 a482 7 All in all, this makes it difficult for you to know which version of `awk' you should run when writing your programs. The best advice I can give here is to check your local documentation. Look for `awk', `oawk', and `nawk', as well as for `gawk'. It is likely that you already have some version of new `awk' on your system, which is what you should use when running your programs. (Of course, if you're reading this Info file, chances are good that you have `gawk'!) d484 2 a485 4 Throughout this Info file, whenever we refer to a language feature that should be available in any complete implementation of POSIX `awk', we simply use the term `awk'. When referring to a feature that is specific to the GNU implementation, we use the term `gawk'. d487 36 a522 1 ---------- Footnotes ---------- d524 5 a528 1 (1) Often, these systems use `gawk' for their `awk' implementation! d530 2 a531 2  File: gawk.info, Node: This Manual, Next: Conventions, Prev: Names, Up: Preface d533 5 a537 2 Using This Book =============== d539 15 a553 23 The term `awk' refers to a particular program as well as to the language you use to tell this program what to do. When we need to be careful, we call the language "the `awk' language," and the program "the `awk' utility." This Info file explains both the `awk' language and how to run the `awk' utility. The term "`awk' program" refers to a program written by you in the `awk' programming language. Primarily, this Info file explains the features of `awk', as defined in the POSIX standard. It does so in the context of the `gawk' implementation. While doing so, it also attempts to describe important differences between `gawk' and other `awk' implementations.(1) Finally, any `gawk' features that are not in the POSIX standard for `awk' are noted. There are subsections labelled as *Advanced Notes* scattered throughout the Info file. They add a more complete explanation of points that are relevant, but not likely to be of interest on first reading. All appear in the index, under the heading "advanced features." Most of the time, the examples use complete `awk' programs. In some of the more advanced sections, only the part of the `awk' program that illustrates the concept currently being described is shown. d555 3 a557 5 While this Info file is aimed principally at people who have not been exposed to `awk', there is a lot of information here that even the `awk' expert should find useful. In particular, the description of POSIX `awk' and the example programs in *Note Library Functions::, and in *Note Sample Programs::, should be of interest. d559 2 a560 2 *Note Getting Started::, provides the essentials you need to know to begin using `awk'. d562 2 a563 2 *Note Regexp::, introduces regular expressions in general, and in particular the flavors supported by POSIX `awk' and `gawk'. d565 6 a570 3 *Note Reading Files::, describes how `awk' reads your data. It introduces the concepts of records and fields, as well as the `getline' command. I/O redirection is first described here. d572 3 a574 2 *Note Printing::, describes how `awk' programs can produce output with `print' and `printf'. d576 6 a581 2 *Note Expressions::, describes expressions, which are the basic building blocks for getting most things done in a program. d583 1 a583 3 *Note Patterns and Actions::, describes how to write patterns for matching records, actions for doing something when a record is matched, and the built-in variables `awk' and `gawk' use. d585 1 a585 3 *Note Arrays::, covers `awk''s one-and-only data structure: associative arrays. Deleting array elements and whole arrays is also described, as well as sorting arrays in `gawk'. d587 1 a587 2 *Note Functions::, describes the built-in functions `awk' and `gawk' provide, as well as how to define your own functions. d589 1 a589 2 *Note Internationalization::, describes special features in `gawk' for translating program messages into different languages at runtime. d591 1 a591 4 *Note Advanced Features::, describes a number of `gawk'-specific advanced features. Of particular note are the abilities to have two-way communications with another process, perform TCP/IP networking, and profile your `awk' programs. d593 2 a594 2 *Note Invoking Gawk::, describes how to run `gawk', the meaning of its command-line options, and how it finds `awk' program source files. d596 1 a596 3 *Note Library Functions::, and *Note Sample Programs::, provide many sample `awk' programs. Reading them allows you to see `awk' solving real problems. d598 5 a602 3 *Note Language History::, describes how the `awk' language has evolved since first release to present. It also describes how `gawk' has acquired features over time. d604 2 a605 4 *Note Installation::, describes how to get `gawk', how to compile it under Unix, and how to compile and use it on different non-Unix systems. It also describes how to report bugs in `gawk' and where to get three other freely available implementations of `awk'. d607 2 a608 3 *Note Notes::, describes how to disable `gawk''s extensions, as well as how to contribute new code to `gawk', how to write extension libraries, and some possible future directions for `gawk' development. d610 37 a646 4 *Note Basic Concepts::, provides some very cursory background material for those who are completely unfamiliar with computer programming. Also centralized there is a discussion of some of the issues surrounding floating-point numbers. d648 6 a653 3 The *Note Glossary::, defines most, if not all, the significant terms used throughout the book. If you find terms that you aren't familiar with, try looking them up here. d655 2 a656 3 *Note Copying::, and *Note GNU Free Documentation License::, present the licenses that cover the `gawk' source code and this Info file, respectively. d658 2 a659 1 ---------- Footnotes ---------- d661 5 a665 2 (1) All such differences appear in the index under the entry "differences in `awk' and `gawk'." d668 1 a668 1 File: gawk.info, Node: Conventions, Next: Manual History, Prev: This Manual, Up: Preface d675 2 a676 2 both the printed and online versions of the documentation. This minor node briefly documents the typographical conventions used in Texinfo. d678 1 a678 1 Examples you would type at the command-line are preceded by the d693 3 a695 19 key and another key, at the same time. For example, a `Ctrl-d' is typed by first pressing and holding the `CONTROL' key, next pressing the `d' key and finally releasing both keys. Dark Corners ............ Dark corners are basically fractal -- no matter how much you illuminate, there's always a smaller but darker one. Brian Kernighan Until the POSIX standard (and `The Gawk Manual'), many features of `awk' were either poorly documented or not documented at all. Descriptions of such features (often called "dark corners") are noted in this Info file with "(d.c.)". They also appear in the index under the heading "dark corner." As noted by the opening quote, though, any coverage of dark corners is, by definition, something that is incomplete. d698 1 a698 1 File: gawk.info, Node: Manual History, Next: How To Contribute, Prev: Conventions, Up: Preface d700 2 a701 2 The GNU Project and This Book ============================= d703 6 a708 5 The Free Software Foundation (FSF) is a nonprofit organization dedicated to the production and distribution of freely distributable software. It was founded by Richard M. Stallman, the author of the original Emacs editor. GNU Emacs is the most widely used version of Emacs today. d710 6 a715 10 The GNU(1) Project is an ongoing effort on the part of the Free Software Foundation to create a complete, freely distributable, POSIX-compliant computing environment. The FSF uses the "GNU General Public License" (GPL) to ensure that their software's source code is always available to the end user. A copy of the GPL is included for your reference (*note Copying::). The GPL applies to the C language source code for `gawk'. To find out more about the FSF and the GNU Project online, see the GNU Project's home page (http://www.gnu.org). This Info file may also be read from their web site (http://www.gnu.org/manual/gawk/). d717 11 a727 5 A shell, an editor (Emacs), highly portable optimizing C, C++, and Objective-C compilers, a symbolic debugger and dozens of large and small utilities (such as `gawk'), have all been completed and are freely available. The GNU operating system kernel (the HURD), has been released but is still in an early stage of development. d729 6 a734 35 Until the GNU operating system is more fully developed, you should consider using GNU/Linux, a freely distributable, Unix-like operating system for Intel 80386, DEC Alpha, Sun SPARC, IBM S/390, and other systems.(2) There are many books on GNU/Linux. One that is freely available is `Linux Installation and Getting Started', by Matt Welsh. Many GNU/Linux distributions are often available in computer stores or bundled on CD-ROMs with books about Linux. (There are three other freely available, Unix-like operating systems for 80386 and other systems: NetBSD, FreeBSD, and OpenBSD. All are based on the 4.4-Lite Berkeley Software Distribution, and they use recent versions of `gawk' for their versions of `awk'.) The Info file itself has gone through a number of previous editions. Paul Rubin wrote the very first draft of `The GAWK Manual'; it was around 40 pages in size. Diane Close and Richard Stallman improved it, yielding a version that was around 90 pages long and barely described the original, "old" version of `awk'. I started working with that version in the fall of 1988. As work on it progressed, the FSF published several preliminary versions (numbered 0.X). In 1996, Edition 1.0 was released with `gawk' 3.0.0. The FSF published the first two editions under the title `The GNU Awk User's Guide'. This edition maintains the basic structure of Edition 1.0, but with significant additional material, reflecting the host of new features in `gawk' version 3.1. Of particular note is *Note Array Sorting::, as well as *Note Bitwise Functions::, *Note Internationalization::, and also *Note Advanced Features::, and *Note Dynamic Extensions::. `GAWK: Effective AWK Programming' will undoubtedly continue to evolve. An electronic version comes with the `gawk' distribution from the FSF. If you find an error in this Info file, please report it! *Note Bugs::, for information on submitting problem reports electronically, or write to me in care of the publisher. d736 17 a752 1 ---------- Footnotes ---------- d754 9 a762 95 (1) GNU stands for "GNU's not Unix." (2) The terminology "GNU/Linux" is explained in the *Note Glossary::.  File: gawk.info, Node: How To Contribute, Next: Acknowledgments, Prev: Manual History, Up: Preface How to Contribute ================= As the maintainer of GNU `awk', I am starting a collection of publicly available `awk' programs. For more information, see `ftp://ftp.freefriends.org/arnold/Awkstuff'. If you have written an interesting `awk' program, or have written a `gawk' extension that you would like to share with the rest of the world, please contact me (). Making things available on the Internet helps keep the `gawk' distribution down to manageable size.  File: gawk.info, Node: Acknowledgments, Prev: How To Contribute, Up: Preface Acknowledgments =============== The initial draft of `The GAWK Manual' had the following acknowledgments: Many people need to be thanked for their assistance in producing this manual. Jay Fenlason contributed many ideas and sample programs. Richard Mlynarik and Robert Chassell gave helpful comments on drafts of this manual. The paper `A Supplemental Document for `awk'' by John W. Pierce of the Chemistry Department at UC San Diego, pinpointed several issues relevant both to `awk' implementation and to this manual, that would otherwise have escaped us. I would like to acknowledge Richard M. Stallman, for his vision of a better world and for his courage in founding the FSF and starting the GNU Project. The following people (in alphabetical order) provided helpful comments on various versions of this book, up to and including this edition. Rick Adams, Nelson H.F. Beebe, Karl Berry, Dr. Michael Brennan, Rich Burridge, Claire Cloutier, Diane Close, Scott Deifik, Christopher ("Topher") Eliot, Jeffrey Friedl, Dr. Darrel Hankerson, Michal Jaegermann, Dr. Richard J. LeBlanc, Michael Lijewski, Pat Rankin, Miriam Robbins, Mary Sheehan, and Chuck Toporek. Robert J. Chassell provided much valuable advice on the use of Texinfo. He also deserves special thanks for convincing me _not_ to title this Info file `How To Gawk Politely'. Karl Berry helped significantly with the TeX part of Texinfo. I would like to thank Marshall and Elaine Hartholz of Seattle and Dr. Bert and Rita Schreiber of Detroit for large amounts of quiet vacation time in their homes, which allowed me to make significant progress on this Info file and on `gawk' itself. Phil Hughes of SSC contributed in a very important way by loaning me his laptop GNU/Linux system, not once, but twice, which allowed me to do a lot of work while away from home. David Trueman deserves special credit; he has done a yeoman job of evolving `gawk' so that it performs well and without bugs. Although he is no longer involved with `gawk', working with him on this project was a significant pleasure. The intrepid members of the GNITS mailing list, and most notably Ulrich Drepper, provided invaluable help and feedback for the design of the internationalization features. Nelson Beebe, Martin Brown, Andreas Buening, Scott Deifik, Darrel Hankerson, Isamu Hasegawa, Michal Jaegermann, Ju"rgen Kahrs, Pat Rankin, Kai Uwe Rommel, and Eli Zaretskii (in alphabetical order) make up the `gawk' "crack portability team." Without their hard work and help, `gawk' would not be nearly the fine program it is today. It has been and continues to be a pleasure working with this team of fine people. David and I would like to thank Brian Kernighan of Bell Laboratories for invaluable assistance during the testing and debugging of `gawk', and for help in clarifying numerous points about the language. We could not have done nearly as good a job on either `gawk' or its documentation without his help. Chuck Toporek, Mary Sheehan, and Claire Coutier of O'Reilly & Associates contributed significant editorial help for this Info file for the 3.1 release of `gawk'. I must thank my wonderful wife, Miriam, for her patience through the many versions of this project, for her proofreading, and for sharing me with the computer. I would like to thank my parents for their love, and for the grace with which they raised and educated me. Finally, I also must acknowledge my gratitude to G-d, for the many opportunities He has sent my way, as well as for the gifts He has given me with which to take advantage of those opportunities. d764 4 a767 5 Arnold Robbins Nof Ayalon ISRAEL March, 2001 d770 1 a770 1 File: gawk.info, Node: Getting Started, Next: Regexp, Prev: Preface, Up: Top d778 2 a779 2 keeps processing input lines in this way until it reaches the end of the input files. d783 1 a783 1 describe the data you want to work with and then what to do when you d788 1 a788 1 often refreshingly easy to read and write. d792 4 a795 3 contain "function definitions", an advanced feature that we will ignore for now. *Note User-defined::.) Each rule specifies one pattern to search for and one action to perform upon finding the pattern. d799 2 a800 2 Newlines usually separate rules. Therefore, an `awk' program looks like this: d808 1 d810 1 a810 3 command-line syntax. * Sample Data Files:: Sample data files for use in the `awk' programs illustrated in this Info file. d812 1 a812 2 * Two Rules:: A less simple one-line example using two rules. d817 36 a852 2 * When:: When to use `gawk' and when to use other things. d855 1 a855 1 File: gawk.info, Node: Running gawk, Next: Sample Data Files, Up: Getting Started d866 4 a874 3 This minor node discusses both mechanisms, along with several variations of each. d877 1 a877 2 * One-shot:: Running a short throwaway `awk' program. d883 1 a883 3 * Comments:: Adding documentation to `gawk' programs. * Quoting:: More discussion of shell quoting issues. d886 1 a886 1 File: gawk.info, Node: One-shot, Next: Read Terminal, Up: Running gawk d888 2 a889 2 One-Shot Throwaway `awk' Programs --------------------------------- d902 4 a905 4 file(s). There are single quotes around PROGRAM so the shell won't interpret any `awk' characters as special shell characters. The quotes also cause the shell to treat all of PROGRAM as a single argument for `awk', and allow PROGRAM to be more than one line long. d910 8 a917 1 reliable because there are no other files to misplace. d919 3 a921 1 *Note Very Simple::, presents several short, self-contained programs. d926 1 a926 1 Running `awk' Without Input Files d930 1 a930 1 following command line: d934 10 a943 10 `awk' applies the PROGRAM to the "standard input", which usually means whatever you type on the terminal. This continues until you indicate end-of-file by typing `Ctrl-d'. (On other operating systems, the end-of-file character may be different. For example, on OS/2 and MS-DOS, it is `Ctrl-z'.) As an example, the following program prints a friendly piece of advice (from Douglas Adams's `The Hitchhiker's Guide to the Galaxy'), to keep you from worrying about the complexities of computer programming (`BEGIN' is a feature we haven't discussed yet): d949 2 a950 3 inner double quotes is necessary because of the shell's quoting rules--in particular because it mixes both single quotes and double quotes.(1) d953 2 a954 2 whatever you type on the keyboard to its standard output (why this works is explained shortly). d965 1 a965 7 Ctrl-d ---------- Footnotes ---------- (1) Although we generally recommend the use of single quotes around the program text, double quotes are needed here in order to put the single quote into the message. d973 3 a975 3 Sometimes your `awk' programs can be very long. In this case, it is more convenient to put the program into a separate file. In order to tell `awk' to use that file for its program, you type: d993 7 a999 6 This was explained earlier (*note Read Terminal::). Note that you don't usually need single quotes around the file name that you specify with `-f', because most file names don't contain any of the shell's special characters. Notice that in `advice', the `awk' program did not have single quotes around it. The quotes are only needed for programs that are provided on the `awk' command line. d1003 1 a1003 1 the execution of the `awk' program but it does make "housekeeping" d1014 3 a1016 2 many Unix systems(1) as well as on the GNU system. For example, you could update the file `advice' to look like this: d1020 1 a1020 1 BEGIN { print "Don't Panic!" } d1022 3 a1024 3 After making this file executable (with the `chmod' utility), simply type `advice' at the shell and the system arranges to run `awk'(2) as if you had typed `awk -f advice': a1025 1 $ chmod +x advice d1029 2 a1030 6 (We assume you have the current directory in your shell's search path variable (typically `$PATH'). If not, you may need to type `./advice' at the shell.) Self-contained `awk' scripts are useful when you want to write a program that users can invoke without their having to know that the d1033 3 a1035 2 Advanced Notes: Portability Issues with `#!' -------------------------------------------- d1037 2 a1038 2 Some systems limit the length of the interpreter name to 32 characters. Often, this can be dealt with by using a symbolic link. d1040 9 a1048 11 You should not put more than one argument on the `#!' line after the path to `awk'. It does not work. The operating system treats the rest of the line as a single argument and passes it to `awk'. Doing this leads to confusing behavior--most likely a usage diagnostic of some sort from `awk'. Finally, the value of `ARGV[0]' (*note Built-in Variables::) varies depending upon your operating system. Some systems put `awk' there, some put the full pathname of `awk' (such as `/bin/awk'), and some put the name of your script (`advice'). Don't rely on the value of `ARGV[0]' to provide your script name. d1052 2 a1053 2 (1) The `#!' mechanism works on Linux systems, systems derived from the 4.4-Lite Berkeley Software Distribution, and most commercial Unix d1056 2 a1057 2 (2) The line beginning with `#!' lists the full file name of an interpreter to run and an optional initial command-line argument to d1061 1 a1061 1 of the `awk' program. The rest of the argument list contains either d1065 1 a1065 1 File: gawk.info, Node: Comments, Next: Quoting, Prev: Executable Scripts, Up: Running gawk d1071 4 a1074 4 of human readers; it is not really an executable part of the program. Comments can explain what the program does and how it works. Nearly all programming languages have provisions for comments, as programs are typically hard to understand without them. d1077 1 a1077 1 character (`#') and continues to the end of the line. The `#' does not d1086 4 a1089 14 You can put comment lines into keyboard-composed throwaway `awk' programs, but this usually isn't very useful; the purpose of a comment is to help you or another person understand the program when reading it at a later time. *Caution:* As mentioned in *Note One-shot::, you can enclose small to medium programs in single quotes, in order to keep your shell scripts self-contained. When doing so, _don't_ put an apostrophe (i.e., a single quote) into a comment (or anywhere else in your program). The shell interprets the quote as the closing quote for the entire program. As a result, usually the shell prints a message about mismatched quotes, and if `awk' actually runs, it will probably print strange messages about syntax errors. For example, look at the following: d1091 2 a1092 2 $ awk '{ print "hello" } # let's be cute' > d1094 2 a1095 4 The shell sees that the first two quotes match, and that a new quoted object begins at the end of the command line. It therefore prompts with the secondary prompt, waiting for more input. With Unix `awk', closing the quoted string produces this result: d1097 5 a1101 4 $ awk '{ print "hello" } # let's be cute' > ' error--> awk: can't open file be error--> source line number 1 d1103 1 a1103 3 Putting a backslash before the single quote in `let's' wouldn't help, since backslashes are not special inside single quotes. The next node describes the shell's quoting rules. d1105 3 a1107 2  File: gawk.info, Node: Quoting, Prev: Comments, Up: Running gawk d1109 7 a1115 2 Shell-Quoting Issues -------------------- d1117 1 a1117 5 For short to medium length `awk' programs, it is most convenient to enter the program on the `awk' command line. This is best done by enclosing the entire program in single quotes. This is true whether you are entering the program interactively at the shell prompt, or writing it as part of a larger shell script: d1119 5 a1123 1 awk 'PROGRAM TEXT' INPUT-FILE1 INPUT-FILE2 ... d1125 4 a1128 4 Once you are working with the shell, it is helpful to have a basic knowledge of shell quoting rules. The following rules apply only to POSIX-compliant, Bourne-style shells (such as `bash', the GNU Bourne-Again Shell). If you use `csh', you're on your own. d1130 5 a1134 3 * Quoted items can be concatenated with nonquoted items as well as with other quoted items. The shell turns everything into one argument for the command. d1136 2 a1137 3 * Preceding any single character with a backslash (`\') quotes that character. The shell removes the backslash and passes the quoted character on to the command. d1139 2 a1140 5 * Single quotes protect everything between the opening and closing quotes. The shell does no interpretation of the quoted text, passing it on verbatim to the command. It is _impossible_ to embed a single quote inside single-quoted text. Refer back to *Note Comments::, for an example of what happens if you try. d1142 5 a1146 4 * Double quotes protect most things between the opening and closing quotes. The shell does at least variable and command substitution on the quoted text. Different shells may do additional kinds of processing on double-quoted text. d1148 4 a1151 7 Since certain characters within double-quoted text are processed by the shell, they must be "escaped" within the text. Of note are the characters `$', ``', `\', and `"', all of which must be preceded by a backslash within double-quoted text if they are to be passed on literally to the program. (The leading backslash is stripped first.) Thus, the example seen in *Note Read Terminal::, is applicable: d1153 1 a1153 2 $ awk "BEGIN { print \"Don't Panic!\" }" -| Don't Panic! d1155 2 a1156 1 Note that the single quote is not special within double quotes. d1158 8 a1165 4 * Null strings are removed when they occur as part of a non-null command-line argument, while explicit non-null objects are kept. For example, to specify that the field separator `FS' should be set to the null string, use: d1167 2 a1168 1 awk -F "" 'PROGRAM' FILES # correct d1170 15 a1184 1 Don't use this: d1186 2 a1187 1 awk -F"" 'PROGRAM' FILES # wrong! d1189 2 a1190 4 In the second case, `awk' will attempt to use the text of the program as the value of `FS', and the first file name as the text of the program! This results in syntax errors at best, and confusing behavior at worst. d1192 2 a1193 2 Mixing single and double quotes is difficult. You have to resort to shell quoting tricks, like this: d1195 5 a1199 2 $ awk 'BEGIN { print "Here is a single quote <'"'"'>" }' -| Here is a single quote <'> d1201 2 a1202 2 This program consists of three concatenated quoted strings. The first and the third are single-quoted, the second is double-quoted. d1204 10 a1213 1 This can be "simplified" to: d1215 8 a1222 285 $ awk 'BEGIN { print "Here is a single quote <'\''>" }' -| Here is a single quote <'> Judge for yourself which of these two is the more readable. Another option is to use double quotes, escaping the embedded, `awk'-level double quotes: $ awk "BEGIN { print \"Here is a single quote <'>\" }" -| Here is a single quote <'> This option is also painful, because double quotes, backslashes, and dollar signs are very common in `awk' programs. If you really need both single and double quotes in your `awk' program, it is probably best to move it into a separate file, where the shell won't be part of the picture, and you can say what you mean.  File: gawk.info, Node: Sample Data Files, Next: Very Simple, Prev: Running gawk, Up: Getting Started Data Files for the Examples =========================== Many of the examples in this Info file take their input from two sample data files. The first, `BBS-list', represents a list of computer bulletin board systems together with information about those systems. The second data file, called `inventory-shipped', contains information about monthly shipments. In both files, each line is considered to be one "record". In the data file `BBS-list', each record contains the name of a computer bulletin board, its phone number, the board's baud rate(s), and a code for the number of hours it is operational. An `A' in the last column means the board operates 24 hours a day. A `B' in the last column means the board only operates on evening and weekend hours. A `C' means the board operates only on weekends: aardvark 555-5553 1200/300 B alpo-net 555-3412 2400/1200/300 A barfly 555-7685 1200/300 A bites 555-1675 2400/1200/300 A camelot 555-0542 300 C core 555-2912 1200/300 C fooey 555-1234 2400/1200/300 B foot 555-6699 1200/300 B macfoo 555-6480 1200/300 A sdace 555-3430 2400/1200/300 A sabafoo 555-2127 1200/300 C The data file `inventory-shipped' represents information about shipments during the year. Each record contains the month, the number of green crates shipped, the number of red boxes shipped, the number of orange bags shipped, and the number of blue packages shipped, respectively. There are 16 entries, covering the 12 months of last year and the first four months of the current year. Jan 13 25 15 115 Feb 15 32 24 226 Mar 15 24 34 228 Apr 31 52 63 420 May 16 34 29 208 Jun 31 42 75 492 Jul 24 34 67 436 Aug 15 34 47 316 Sep 13 55 37 277 Oct 29 54 68 525 Nov 20 87 82 577 Dec 17 35 61 401 Jan 21 36 64 620 Feb 26 58 80 652 Mar 24 75 70 495 Apr 21 70 74 514 If you are reading this in GNU Emacs using Info, you can copy the regions of text showing these sample files into your own test files. This way you can try out the examples shown in the remainder of this document. You do this by using the command `M-x write-region' to copy text from the Info file into a file for use with `awk' (*Note Miscellaneous File Operations: (emacs)Misc File Ops, for more information). Using this information, create your own `BBS-list' and `inventory-shipped' files and practice what you learn in this Info file. If you are using the stand-alone version of Info, see *Note Extract Program::, for an `awk' program that extracts these data files from `gawk.texi', the Texinfo source file for this Info file.  File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Sample Data Files, Up: Getting Started Some Simple Examples ==================== The following command runs a simple `awk' program that searches the input file `BBS-list' for the character string `foo' (a grouping of characters is usually called a "string"; the term "string" is based on similar usage in English, such as "a string of pearls," or "a string of cars in a train"): awk '/foo/ { print $0 }' BBS-list When lines containing `foo' are found, they are printed because `print $0' means print the current line. (Just `print' by itself means the same thing, so we could have written that instead.) You will notice that slashes (`/') surround the string `foo' in the `awk' program. The slashes indicate that `foo' is the pattern to search for. This type of pattern is called a "regular expression", which is covered in more detail later (*note Regexp::). The pattern is allowed to match parts of words. There are single quotes around the `awk' program so that the shell won't interpret any of it as special shell characters. Here is what this program prints: $ awk '/foo/ { print $0 }' BBS-list -| fooey 555-1234 2400/1200/300 B -| foot 555-6699 1200/300 B -| macfoo 555-6480 1200/300 A -| sabafoo 555-2127 1200/300 C In an `awk' rule, either the pattern or the action can be omitted, but not both. If the pattern is omitted, then the action is performed for _every_ input line. If the action is omitted, the default action is to print all lines that match the pattern. Thus, we could leave out the action (the `print' statement and the curly braces) in the previous example and the result would be the same: all lines matching the pattern `foo' are printed. By comparison, omitting the `print' statement but retaining the curly braces makes an empty action that does nothing (i.e., no lines are printed). Many practical `awk' programs are just a line or two. Following is a collection of useful, short programs to get you started. Some of these programs contain constructs that haven't been covered yet. (The description of the program will give you a good idea of what is going on, but please read the rest of the Info file to become an `awk' expert!) Most of the examples use a data file named `data'. This is just a placeholder; if you use these programs yourself, substitute your own file names for `data'. For future reference, note that there is often more than one way to do things in `awk'. At some point, you may want to look back at these examples and see if you can come up with different ways to do the same things shown here: * Print the length of the longest input line: awk '{ if (length($0) > max) max = length($0) } END { print max }' data * Print every line that is longer than 80 characters: awk 'length($0) > 80' data The sole rule has a relational expression as its pattern and it has no action--so the default action, printing the record, is used. * Print the length of the longest line in `data': expand data | awk '{ if (x < length()) x = length() } END { print "maximum line length is " x }' The input is processed by the `expand' utility to change tabs into spaces, so the widths compared are actually the right-margin columns. * Print every line that has at least one field: awk 'NF > 0' data This is an easy way to delete blank lines from a file (or rather, to create a new file similar to the old file but from which the blank lines have been removed). * Print seven random numbers from 0 to 100, inclusive: awk 'BEGIN { for (i = 1; i <= 7; i++) print int(101 * rand()) }' * Print the total number of bytes used by FILES: ls -l FILES | awk '{ x += $5 } END { print "total bytes: " x }' * Print the total number of kilobytes used by FILES: ls -l FILES | awk '{ x += $5 } END { print "total K-bytes: " (x + 1023)/1024 }' * Print a sorted list of the login names of all users: awk -F: '{ print $1 }' /etc/passwd | sort * Count the lines in a file: awk 'END { print NR }' data * Print the even-numbered lines in the data file: awk 'NR % 2 == 0' data If you use the expression `NR % 2 == 1' instead, the program would print the odd-numbered lines.  File: gawk.info, Node: Two Rules, Next: More Complex, Prev: Very Simple, Up: Getting Started An Example with Two Rules ========================= The `awk' utility reads the input files one line at a time. For each line, `awk' tries the patterns of each of the rules. If several patterns match, then several actions are run in the order in which they appear in the `awk' program. If no patterns match, then no actions are run. After processing all the rules that match the line (and perhaps there are none), `awk' reads the next line. (However, *note Next Statement::, and also *note Nextfile Statement::). This continues until the program reaches the end of the file. For example, the following `awk' program contains two rules: /12/ { print $0 } /21/ { print $0 } The first rule has the string `12' as the pattern and `print $0' as the action. The second rule has the string `21' as the pattern and also has `print $0' as the action. Each rule's action is enclosed in its own pair of braces. This program prints every line that contains the string `12' _or_ the string `21'. If a line contains both strings, it is printed twice, once by each rule. This is what happens if we run this program on our two sample data files, `BBS-list' and `inventory-shipped': $ awk '/12/ { print $0 } > /21/ { print $0 }' BBS-list inventory-shipped -| aardvark 555-5553 1200/300 B -| alpo-net 555-3412 2400/1200/300 A -| barfly 555-7685 1200/300 A -| bites 555-1675 2400/1200/300 A -| core 555-2912 1200/300 C -| fooey 555-1234 2400/1200/300 B -| foot 555-6699 1200/300 B -| macfoo 555-6480 1200/300 A -| sdace 555-3430 2400/1200/300 A -| sabafoo 555-2127 1200/300 C -| sabafoo 555-2127 1200/300 C -| Jan 21 36 64 620 -| Apr 21 70 74 514 Note how the line beginning with `sabafoo' in `BBS-list' was printed twice, once for each rule.  File: gawk.info, Node: More Complex, Next: Statements/Lines, Prev: Two Rules, Up: Getting Started A More Complex Example ====================== Now that we've mastered some simple tasks, let's look at what typical `awk' programs do. This example shows how `awk' can be used to summarize, select, and rearrange the output of another utility. It uses features that haven't been covered yet, so don't worry if you don't understand all the details: ls -l | awk '$6 == "Nov" { sum += $5 } END { print sum }' This command prints the total number of bytes in all the files in the current directory that were last modified in November (of any year). (1) The `ls -l' part of this example is a system command that gives you a listing of the files in a directory, including each file's size and the date the file was last modified. Its output looks like this: -rw-r--r-- 1 arnold user 1933 Nov 7 13:05 Makefile -rw-r--r-- 1 arnold user 10809 Nov 7 13:03 awk.h -rw-r--r-- 1 arnold user 983 Apr 13 12:14 awk.tab.h -rw-r--r-- 1 arnold user 31869 Jun 15 12:20 awk.y -rw-r--r-- 1 arnold user 22414 Nov 7 13:03 awk1.c -rw-r--r-- 1 arnold user 37455 Nov 7 13:03 awk2.c -rw-r--r-- 1 arnold user 27511 Dec 9 13:07 awk3.c -rw-r--r-- 1 arnold user 7989 Nov 7 13:03 awk4.c d1228 1 a1228 1 The sixth, seventh, and eighth fields contain the month, day, and time, d1230 1 a1230 1 contains the name of the file.(2) d1233 1 a1233 1 whether the sixth field of the output from `ls -l' matches the string d1235 1 a1235 1 action `sum += $5' is performed. This adds the fifth field (the file's d1237 3 a1239 3 reading all the input lines, `sum' is the total of the sizes of the files whose lines matched the pattern. (This works because `awk' variables are automatically initialized to zero.) d1242 2 a1243 2 `END' rule executes and prints the value of `sum'. In this example, the value of `sum' is 80600. d1246 5 a1250 18 (*note Action Overview::). Before you can move on to more advanced `awk' programming, you have to know how `awk' interprets your input and displays your output. By manipulating fields and using `print' statements, you can produce some very useful and impressive-looking reports. ---------- Footnotes ---------- (1) In the C shell (`csh'), you need to type a semicolon and then a backslash at the end of the first line; see *Note Statements/Lines::, for an explanation. In a POSIX-compliant shell, such as the Bourne shell or `bash', you can type the example as shown. If the command `echo $path' produces an empty output line, you are most likely using a POSIX-compliant shell. Otherwise, you are probably using the C shell or a shell derived from it. (2) On some very old systems, you may need to use `ls -lg' to get this output. d1264 1 a1264 2 However, `gawk' ignores newlines after any of the following symbols and keywords: d1268 4 a1271 1 A newline at any other point is considered the end of the statement.(1) d1275 3 a1277 3 ending the first line with a backslash character (`\'). The backslash must be the final character on the line in order to be recognized as a continuation character. A backslash is allowed anywhere in the d1285 18 a1302 17 in this Info file. In `gawk', there is no limit on the length of a line, so backslash continuation is never strictly necessary; it just makes programs more readable. For this same reason, as well as for clarity, we have kept most statements short in the sample programs presented throughout the Info file. Backslash continuation is most useful when your `awk' program is in a separate source file instead of entered from the command line. You should also note that many `awk' implementations are more particular about where you may use backslash continuation. For example, they may not allow you to split a string constant using backslash continuation. Thus, for maximum portability of your `awk' programs, it is best not to split your lines in the middle of a regular expression or a string. *Caution:* _Backslash continuation does not work as described with the C shell._ It works for `awk' programs in files and for one-shot programs, _provided_ you are using a POSIX-compliant shell, such as the Unix Bourne shell or `bash'. But the C shell behaves differently! d1304 1 a1304 1 Note also that when using the C shell, _every_ newline in your awk a1315 9 Compare the previous example to how it is done with a POSIX-compliant shell: $ awk 'BEGIN { > print \ > "hello, world" > }' -| hello, world d1318 2 a1319 2 separate lines, you _must_ use backslash continuation; there is no other option. d1321 3 a1323 3 Another thing to keep in mind is that backslash continuation and comments do not mix. As soon as `awk' sees the `#' that starts a comment, it ignores _everything_ on the rest of the line. For example: d1331 4 a1334 4 In this case, it looks like the backslash would continue the comment onto the next line. However, the backslash-newline combination is never even noticed because it is "hidden" inside the comment. Thus, the `BEGIN' is noted as a syntax error. d1337 5 a1341 4 put more than one of them on a line. This is accomplished by separating the statements with a semicolon (`;'). This also applies to the rules themselves. Thus, the program shown at the start of this minor node could also be written this way: d1345 3 a1347 11 *Note:* The requirement that states that rules on the same line must be separated with a semicolon was not in the original `awk' language; it was added for consistency with the treatment of statements within an action. ---------- Footnotes ---------- (1) The `?' and `:' referred to here is the three-operand conditional expression described in *Note Conditional Exp::. Splitting lines after `?' and `:' is a minor `gawk' extension; if `--posix' is specified (*note Options::), then this extension is disabled. d1355 4 a1358 4 The `awk' language provides a number of predefined, or "built-in", variables that your programs can use to get information from `awk'. There are other variables your program can set as well to control how `awk' processes your data. d1361 1 a1361 3 common computational and string-related operations. `gawk' provides built-in functions for working with timestamps, performing bit manipulation, and for runtime string translation. d1365 2 a1366 1 systematically in *Note Built-in Variables::, and *Note Built-in::. d1374 7 a1380 7 Now that you've seen some of what `awk' can do, you might wonder how `awk' could be useful for you. By using utility programs, advanced patterns, field separators, arithmetic statements, and other selection criteria, you can produce much more complex output. The `awk' language is very useful for producing reports from large amounts of raw data, such as summarizing information from the output of other utility programs like `ls'. (*Note More Complex::.) d1385 1 a1385 1 used once, and thrown away. Because `awk' programs are interpreted, you d1390 4 a1393 4 retargetable assembler for eight-bit microprocessors (*note Glossary::, for more information), and a microcode assembler for a special-purpose Prolog computer. However, `awk''s capabilities are strained by tasks of such complexity. d1400 1 a1400 1 utilities. More conventional languages, such as C, C++, and Java, offer d1407 69 a1475 1 File: gawk.info, Node: Regexp, Next: Reading Files, Prev: Getting Started, Up: Top d1482 1 a1482 1 `awk' programming, their format and use deserve a separate major node. d1485 7 a1491 6 that matches every input record whose text belongs to that set. The simplest regular expression is a sequence of letters, numbers, or both. Such a regexp matches any string that contains that sequence. Thus, the regexp `foo' matches any string containing `foo'. Therefore, the pattern `/foo/' matches any input record containing the three characters `foo' _anywhere_ in the record. Other kinds of regexps let d1497 1 a1497 1 * Escape Sequences:: How to write nonprinting characters. a1498 1 * Character Lists:: What can go between `[...]'. a1502 1 * Locales:: How the locale affects things. d1505 1 a1505 1 File: gawk.info, Node: Regexp Usage, Next: Escape Sequences, Up: Regexp d1513 2 a1514 3 text in order to succeed.) For example, the following prints the second field of each record that contains the string `foo' anywhere in it: d1522 35 a1556 38 `~' (tilde), `~' operator Regular expressions can also be used in matching expressions. These expressions allow you to specify the string to match against; it need not be the entire current input record. The two operators `~' and `!~' perform regular expression comparisons. Expressions using these operators can be used as patterns, or in `if', `while', `for', and `do' statements. (*Note Statements::.) For example: EXP ~ /REGEXP/ is true if the expression EXP (taken as a string) matches REGEXP. The following example matches, or selects, all input records with the uppercase letter `J' somewhere in the first field: $ awk '$1 ~ /J/' inventory-shipped -| Jan 13 25 15 115 -| Jun 31 42 75 492 -| Jul 24 34 67 436 -| Jan 21 36 64 620 So does this: awk '{ if ($1 ~ /J/) print }' inventory-shipped This next example is true if the expression EXP (taken as a character string) does _not_ match REGEXP: EXP !~ /REGEXP/ The following example matches, or selects, all input records whose first field _does not_ contain the uppercase letter `J': $ awk '$1 !~ /J/' inventory-shipped -| Feb 15 32 24 226 -| Mar 15 24 34 228 -| Apr 31 52 63 420 -| May 16 34 29 208 ... d1558 3 a1560 3 When a regexp is enclosed in slashes, such as `/foo/', we call it a "regexp constant", much like `5.27' is a numeric constant and `"foo"' is a string constant. d1569 8 a1576 6 (`"foo"') or regexp constants (`/foo/'). Instead, they should be represented with "escape sequences", which are character sequences beginning with a backslash (`\'). One use of an escape sequence is to include a double-quote character in a string constant. Because a plain double quote ends the string, you must use `\"' to represent an actual double-quote character as a part of the string. For example: d1582 12 a1593 12 included normally; you must write `\\' to put one backslash in the string or regexp. Thus, the string whose contents are the two characters `"' and `\' must be written `"\"\\"'. Backslash also represents unprintable characters such as TAB or newline. While there is nothing to stop you from entering most unprintable characters directly in a string constant or regexp constant, they may look ugly. The following table lists all the escape sequences used in `awk' and what they represent. Unless noted otherwise, all these escape sequences apply to both string constants and regexp constants: d1599 1 a1599 2 The "alert" character, `Ctrl-g', ASCII code 7 (BEL). (This usually makes some sort of audible noise.) d1602 1 a1602 1 Backspace, `Ctrl-h', ASCII code 8 (BS). d1605 1 a1605 1 Formfeed, `Ctrl-l', ASCII code 12 (FF). d1608 1 a1608 1 Newline, `Ctrl-j', ASCII code 10 (LF). d1611 1 a1611 1 Carriage return, `Ctrl-m', ASCII code 13 (CR). d1614 1 a1614 1 Horizontal TAB, `Ctrl-i', ASCII code 9 (HT). d1617 1 a1617 1 Vertical tab, `Ctrl-k', ASCII code 11 (VT). d1620 2 a1621 2 The octal value NNN, where NNN stands for 1 to 3 digits between `0' and `7'. For example, the code for the ASCII ESC (escape) d1625 4 a1628 4 The hexadecimal value HH, where HH stands for a sequence of hexadecimal digits (`0'-`9', and either `A'-`F' or `a'-`f'). Like the same construct in ISO C, the escape sequence continues until the first nonhexadecimal digit is seen. However, using more than d1633 5 a1637 5 A literal slash (necessary for regexp constants only). This expression is used when you want to write a regexp constant that contains a slash. Because the regexp is delimited by slashes, you need to escape the slash that is part of the pattern, in order to tell `awk' to keep processing the rest of the regexp. d1640 20 a1659 10 A literal double quote (necessary for string constants only). This expression is used when you want to write a string constant that contains a double quote. Because the string is delimited by double quotes, you need to escape the quote that is part of the string, in order to tell `awk' to keep processing the rest of the string. In `gawk', a number of additional two-character sequences that begin with a backslash have special meaning in regexps. *Note GNU Regexp Operators::. d1662 4 a1665 4 previous list and not listed in *Note GNU Regexp Operators::, means that the next character should be taken literally, even if it would normally be a regexp operator. For example, `/a\+b/' matches the three characters `a+b'. d1668 14 a1681 1 character not shown in the previous list. d1685 1 a1685 1 * The escape sequences in the table above are always processed first, d1689 4 a1692 3 * `gawk' processes both regexp constants and dynamic regexps (*note Computed Regexps::), for the special operators listed in *Note GNU Regexp Operators::. d1694 1 a1694 1 * A backslash before any other character means to treat that a1696 33 Advanced Notes: Backslash Before Regular Characters --------------------------------------------------- If you place a backslash in a string constant before something that is not one of the characters previously listed, POSIX `awk' purposely leaves what happens as undefined. There are two choices: Strip the backslash out This is what Unix `awk' and `gawk' both do. For example, `"a\qc"' is the same as `"aqc"'. (Because this is such an easy bug both to introduce and to miss, `gawk' warns you about it.) Consider `FS = "[ \t]+\|[ \t]+"' to use vertical bars surrounded by whitespace as the field separator. There should be two backslashes in the string `FS = "[ \t]+\\|[ \t]+"'.) Leave the backslash alone Some other `awk' implementations do this. In such implementations, typing `"a\qc"' is the same as typing `"a\\qc"'. Advanced Notes: Escape Sequences for Metacharacters --------------------------------------------------- Suppose you use an octal or hexadecimal escape to represent a regexp metacharacter. (See *Note Regexp Operators::.) Does `awk' treat the character as a literal character or as a regexp operator? Historically, such characters were taken literally. (d.c.) However, the POSIX standard indicates that they should be treated as real metacharacters, which is what `gawk' does. In compatibility mode (*note Options::), `gawk' treats the characters represented by octal and hexadecimal escape sequences literally when used in regexp constants. Thus, `/a\52b/' is equivalent to `/a\*b/'. d1698 1 a1698 1 File: gawk.info, Node: Regexp Operators, Next: Character Lists, Prev: Escape Sequences, Up: Regexp d1703 3 a1705 3 You can combine regular expressions with special characters, called "regular expression operators" or "metacharacters", to increase the power and versatility of regular expressions. d1708 7 a1714 6 valid inside a regexp. They are introduced by a `\' and are recognized and converted into corresponding real characters as the very first step in processing regexps. Here is a list of metacharacters. All characters that are not escape sequences and that are not listed in the table stand for themselves: d1718 5 a1722 1 matching. For example, `\$' matches the character `$'. d1725 8 a1732 5 This matches the beginning of a string. For example, `^@@chapter' matches `@@chapter' at the beginning of a string and can be used to identify chapter beginnings in Texinfo source files. The `^' is known as an "anchor", because it anchors the pattern to match only at the beginning of the string. d1735 2 a1736 2 a line embedded in a string. The condition is not true in the following example: d1742 7 a1748 3 For example, `p$' matches a record that ends with a `p'. The `$' is an anchor and does not match the end of a line embedded in a string. The condition in the following example is not true: d1753 14 a1766 10 This matches any single character, _including_ the newline character. For example, `.P' matches any single character followed by a `P' in a string. Using concatenation, we can make a regular expression such as `U.A', which matches any three-character sequence that begins with `U' and ends with `A'. In strict POSIX mode (*note Options::), `.' does not match the NUL character, which is a character with all bits equal to zero. Otherwise, NUL is just another character. Other versions of `awk' may not be able to match the NUL character. d1769 117 a1885 5 This is called a "character list".(1) It matches any _one_ of the characters that are enclosed in the square brackets. For example, `[MVX]' matches any one of the characters `M', `V', or `X' in a string. A full discussion of what can be inside the square brackets of a character list is given in *Note Character Lists::. d1889 6 a1894 3 the `[' _must_ be a `^'. It matches any characters _except_ those in the square brackets. For example, `[^awk]' matches any character that is not an `a', `w', or `k'. d1897 8 a1904 5 This is the "alternation operator" and it is used to specify alternatives. The `|' has the lowest precedence of all the regular expression operators. For example, `^P|[[:digit:]]' matches any string that matches either `^P' or `[[:digit:]]'. This means it matches any string that starts with `P' or contains a digit. d1907 2 a1908 1 side. d1911 1 a1911 1 Parentheses are used for grouping in regular expressions, as in d1914 2 a1915 3 `@@(samp|code)\{[^}]+\}' matches both `@@code{foo}' and `@@samp{bar}'. (These are Texinfo formatting control sequences. The `+' is explained further on in this list.) d1918 18 a1935 13 This symbol means that the preceding regular expression should be repeated as many times as necessary to find a match. For example, `ph*' applies the `*' symbol to the preceding `h' and looks for matches of one `p' followed by any number of `h's. This also matches just `p' if no `h's are present. The `*' repeats the _smallest_ possible preceding expression. (Use parentheses if you want to repeat a larger expression.) It finds as many repetitions as possible. For example, `awk '/\(c[ad][ad]*r x\)/ { print }' sample' prints every record in `sample' containing a string of the form `(car x)', `(cdr x)', `(cadr x)', and so on. Notice the escaping of the parentheses by preceding them with backslashes. d1938 8 a1945 5 This symbol is similar to `*', except that the preceding expression must be matched at least once. This means that `wh+y' would match `why' and `whhy', but not `wy', whereas `wh*y' would match all three of these strings. The following is a simpler way of writing the last `*' example: d1950 6 a1955 3 This symbol is similar to `*', except that the preceding expression can be matched either once or not at all. For example, `fe?d' matches `fed' and `fd', but nothing else. d1965 1 a1965 1 at least N times: d1968 1 a1968 1 Matches `whhhy', but not `why' or `whhhhy'. d1971 1 a1971 1 Matches `whhhy', `whhhhy', or `whhhhhy', only. d1974 1 a1974 1 Matches `whhy' or `whhhy', and so on. d1977 1 a1977 1 They were added as part of the POSIX standard to make `awk' and d1980 2 a1981 2 However, because old programs may use `{' and `}' in regexp constants, by default `gawk' does _not_ match interval expressions d1983 2 a1984 7 (*note Options::), then interval expressions are allowed in regexps. For new programs that use `{' and `}' in regexp constants, it is good practice to always escape them with a backslash. Then the regexp constants are valid and work the way you want them to, using any version of `awk'.(2) d1991 3 a1993 14 In POSIX `awk' and `gawk', the `*', `+', and `?' operators stand for themselves when there is nothing in the regexp that precedes them. For example, `/+/' matches a literal plus sign. However, many other versions of `awk' treat such a usage as a syntax error. If `gawk' is in compatibility mode (*note Options::), POSIX character classes and interval expressions are not available in regular expressions. ---------- Footnotes ---------- (1) In other literature, you may see a character list referred to as either a "character set", a "character class", or a "bracket expression". d1995 3 a1997 2 (2) Use two backslashes if you're using a string constant with a regexp operator or function. d2000 1 a2000 1 File: gawk.info, Node: Character Lists, Next: GNU Regexp Operators, Prev: Regexp Operators, Up: Regexp d2002 2 a2003 94 Using Character Lists ===================== Within a character list, a "range expression" consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, using the locale's collating sequence and character set. For example, in the default C locale, `[a-dx-z]' is equivalent to `[abcdxyz]'. Many locales sort characters in dictionary order, and in these locales, `[a-dx-z]' is typically not equivalent to `[abcdxyz]'; instead it might be equivalent to `[aBbCcDdxXyYz]', for example. To obtain the traditional interpretation of bracket expressions, you can use the C locale by setting the `LC_ALL' environment variable to the value `C'. To include one of the characters `\', `]', `-', or `^' in a character list, put a `\' in front of it. For example: [d\]] matches either `d' or `]'. This treatment of `\' in character lists is compatible with other `awk' implementations and is also mandated by POSIX. The regular expressions in `awk' are a superset of the POSIX specification for Extended Regular Expressions (EREs). POSIX EREs are based on the regular expressions accepted by the traditional `egrep' utility. "Character classes" are a new feature introduced in the POSIX standard. A character class is a special notation for describing lists of characters that have a specific attribute, but the actual characters can vary from country to country and/or from character set to character set. For example, the notion of what is an alphabetic character differs between the United States and France. A character class is only valid in a regexp _inside_ the brackets of a character list. Character classes consist of `[:', a keyword denoting the class, and `:]'. Here are the character classes defined by the POSIX standard. `[:alnum:]' Alphanumeric characters. `[:alpha:]' Alphabetic characters. `[:blank:]' Space and TAB characters. `[:cntrl:]' Control characters. `[:digit:]' Numeric characters. `[:graph:]' Characters that are both printable and visible. (A space is printable but not visible, whereas an `a' is both.) `[:lower:]' Lowercase alphabetic characters. `[:print:]' Printable characters (characters that are not control characters). `[:punct:]' Punctuation characters (characters that are not letters, digits, control characters, or space characters). `[:space:]' Space characters (such as space, TAB, and formfeed, to name a few). `[:upper:]' Uppercase alphabetic characters. `[:xdigit:]' Characters that are hexadecimal digits. For example, before the POSIX standard, you had to write `/[A-Za-z0-9]/' to match alphanumeric characters. If your character set had other alphabetic characters in it, this would not match them, and if your character set collated differently from ASCII, this might not even match the ASCII alphanumeric characters. With the POSIX character classes, you can write `/[[:alnum:]]/' to match the alphabetic and numeric characters in your character set. Two additional special sequences can appear in character lists. These apply to non-ASCII character sets, which can have single symbols (called "collating elements") that are represented with more than one character. They can also have several characters that are equivalent for "collating", or sorting, purposes. (For example, in French, a plain "e" and a grave-accented "e`" are equivalent.) These sequences are: Collating symbols Multicharacter collating elements enclosed between `[.' and `.]'. For example, if `ch' is a collating element, then `[[.ch.]]' is a regexp that matches this collating element, whereas `[ch]' is a regexp that matches either `c' or `h'. Equivalence classes Locale-specific names for a list of characters that are equal. The name is enclosed between `[=' and `=]'. For example, the name `e' might be used to represent all of "e," "e`," and "e'." In this case, `[[=e=]]' is a regexp that matches any of `e', `e'', or `e`'. These features are very valuable in non-English-speaking locales. *Caution:* The library functions that `gawk' uses for regular expression matching currently recognize only POSIX character classes; they do not recognize collating symbols or equivalence classes.  File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Character Lists, Up: Regexp `gawk'-Specific Regexp Operators ================================ d2007 6 a2012 4 minor node and are specific to `gawk'; they are not available in other `awk' implementations. Most of the additional operators deal with word matching. For our purposes, a "word" is a sequence of one or more letters, digits, or underscores (`_'): d2015 2 a2016 2 Matches any word-constituent character--that is, it matches any letter, digit, or underscore. Think of it as shorthand for d2020 2 a2021 2 Matches any character that is not word-constituent. Think of it as shorthand for `[^[:alnum:]_]'. d2024 2 a2025 2 Matches the empty string at the beginning of a word. For example, `/\/' matches `stow' but not `stowaway'. d2032 3 a2034 3 Matches the empty string at either the beginning or the end of a word (i.e., the word boundar*y*). For example, `\yballs?\y' matches either `ball' or `balls', as a separate word. d2037 5 a2041 3 Matches the empty string that occurs between two word-constituent characters. For example, `/\Brat\B/' matches `crate' but it does not match `dirty rat'. `\B' is essentially the opposite of `\y'. d2044 7 a2050 3 "buffer" is, naturally, an Emacs buffer. For other programs, `gawk''s regexp library routines consider the entire string to match as the buffer. The operators are: d2053 2 a2054 1 Matches the empty string at the beginning of a buffer (string). d2057 1 a2057 1 Matches the empty string at the end of a buffer (string). d2059 3 a2061 3 Because `^' and `$' always work in terms of the beginning and end of strings, these operators don't add any new capabilities for `awk'. They are provided for compatibility with other GNU software. d2063 4 a2066 6 In other GNU software, the word-boundary operator is `\b'. However, that conflicts with the `awk' language's definition of `\b' as backspace, so `gawk' uses a different letter. An alternative method would have been to require two backslashes in the GNU operators, but this was deemed too confusing. The current method of using `\y' for the GNU `\b' appears to be the lesser of two evils. d2068 2 a2069 2 The various command-line options (*note Options::) control how `gawk' interprets characters in regexps: d2072 4 a2075 3 In the default case, `gawk' provides all the facilities of POSIX regexps and the GNU regexp operators described in *Note Regexp Operators::. However, interval expressions are not supported. d2078 1 a2078 1 Only POSIX regexps are supported; the GNU operators are not special d2084 4 a2087 4 not special, interval expressions are not available, nor are the POSIX character classes (`[[:alnum:]]', etc.). Characters described by octal and hexadecimal escape sequences are treated literally, even if they represent regexp metacharacters. d2091 1 a2091 3 been provided. (`--posix' automatically enables interval expressions, so `--re-interval' is redundant when `--posix' is is used.) d2096 1 a2096 1 Case Sensitivity in Matching d2100 3 a2102 3 matching ordinary characters (i.e., not metacharacters) and inside character sets. Thus, a `w' in a regular expression matches only a lowercase `w' and not an uppercase `W'. d2105 9 a2113 8 list--for example, `[Ww]'. However, this can be cumbersome if you need to use it often, and it can make the regular expressions harder to read. There are two alternatives that you might prefer. One way to perform a case-insensitive match at a particular point in the program is to convert the data to a single case, using the `tolower' or `toupper' built-in string functions (which we haven't discussed yet; *note String Functions::). For example: d2117 2 a2118 2 converts the first field to lowercase before matching against it. This works in any POSIX-compliant `awk'. d2121 5 a2125 6 `IGNORECASE' to a nonzero value (*note Built-in Variables::). When `IGNORECASE' is not zero, _all_ regexp and string operations ignore case. Changing the value of `IGNORECASE' dynamically controls the case-sensitivity of the program as it runs. Case is significant by default because `IGNORECASE' (like most variables) is initialized to zero: d2134 22 a2155 21 case-insensitive and other rules case-sensitive, because there is no straightforward way to set `IGNORECASE' just for the pattern of a particular rule.(1) To do this, use either character lists or `tolower'. However, one thing you can do with `IGNORECASE' only is dynamically turn case-sensitivity on or off for all the rules at once. `IGNORECASE' can be set on the command line or in a `BEGIN' rule (*note Other Arguments::; also *note Using BEGIN/END::). Setting `IGNORECASE' from the command line is a way to make a program case-insensitive without having to edit it. Prior to `gawk' 3.0, the value of `IGNORECASE' affected regexp operations only. It did not affect string comparison with `==', `!=', and so on. Beginning with version 3.0, both regexp and string comparison operations are also affected by `IGNORECASE'. Beginning with `gawk' 3.0, the equivalences between upper- and lowercase characters are based on the ISO-8859-1 (ISO Latin-1) character set. This character set is a superset of the traditional 128 ASCII characters, which also provides a number of characters suitable for use with European languages. d2158 2 a2159 9 compatibility mode (*note Options::). Case is always significant in compatibility mode. ---------- Footnotes ---------- (1) Experienced C and C++ programmers will note that it is possible, using something like `IGNORECASE = 1 && /foObAr/ { ... }' and `IGNORECASE = 0 || /foobar/ { ... }'. However, this is somewhat obscure and we don't recommend it. d2167 1 a2167 1 Consider the following: d2171 12 a2182 9 This example uses the `sub' function (which we haven't discussed yet; *note String Functions::) to make a change to the input record. Here, the regexp `/a+/' indicates "one or more `a' characters," and the replacement text is `'. The input contains four `a' characters. `awk' (and POSIX) regular expressions always match the leftmost, _longest_ sequence of input characters that can match. Thus, all four `a' characters are replaced with `' in this example: d2188 7 a2194 5 doing text matching and substitutions with the `match', `sub', `gsub', and `gensub' functions, it is very important. *Note String Functions::, for more information on these functions. Understanding this principle is also important for regexp-based record and field splitting (*note Records::, and also *note Field Separators::). d2197 1 a2197 1 File: gawk.info, Node: Computed Regexps, Next: Locales, Prev: Leftmost Longest, Up: Regexp d2202 21 a2222 21 The righthand side of a `~' or `!~' operator need not be a regexp constant (i.e., a string of characters between slashes). It may be any expression. The expression is evaluated and converted to a string if necessary; the contents of the string are used as the regexp. A regexp that is computed in this way is called a "dynamic regexp": BEGIN { digits_regexp = "[[:digit:]]+" } $0 ~ digits_regexp { print } This sets `digits_regexp' to a regexp that describes one or more digits, and tests whether the input record matches this regexp. When using the `~' and `!~' *Caution:* When using the `~' and `!~' operators, there is a difference between a regexp constant enclosed in slashes and a string constant enclosed in double quotes. If you are going to use a string constant, you have to understand that the string is, in essence, scanned _twice_: the first time when `awk' reads your program, and the second time when it goes to match the string on the lefthand side of the operator with the pattern on the right. This is true of any string-valued expression (such as `digits_regexp', shown previously), not just string constants. d2230 3 a2232 3 one backslash is needed. To do the same thing with a string, you have to type `"\\*"'. The first backslash escapes the second one so that the string actually contains the two characters `\' and `*'. d2236 1 a2236 1 constants," for several reasons: d2238 1 a2238 1 * String constants are more complicated to write and more difficult d2243 3 a2245 3 * It is more efficient to use regexp constants. `awk' can note that you have supplied a regexp and store it internally in a form that makes pattern matching more efficient. When using a string d2247 1 a2247 1 form and then perform the pattern matching. d2249 1 a2249 1 * Using regexp constants is better form; it shows clearly that you d2252 2 a2253 71 Advanced Notes: Using `\n' in Character Lists of Dynamic Regexps ---------------------------------------------------------------- Some commercial versions of `awk' do not allow the newline character to be used inside a character list for a dynamic regexp: $ awk '$0 ~ "[ \t\n]"' error--> awk: newline in character class [ error--> ]... error--> source line number 1 error--> context is error--> >>> <<< But a newline in a regexp constant works with no problem: $ awk '$0 ~ /[ \t\n]/' here is a sample line -| here is a sample line Ctrl-d `gawk' does not have this problem, and it isn't likely to occur often in practice, but it's worth noting for future reference.  File: gawk.info, Node: Locales, Prev: Computed Regexps, Up: Regexp Where You Are Makes A Difference ================================ Modern systems support the notion of "locales": a way to tell the system about the local character set and language. The current locale setting can affect the way regexp matching works, often in surprising ways. In particular, many locales do case-insensitive matching, even when you may have specified characters of only one particular case. The following example uses the `sub' function, which does text replacement (*note String Functions::). Here, the intent is to remove trailing uppercase characters: $ echo something1234abc | gawk '{ sub("[A-Z]*$", ""); print }' -| something1234 This output is unexpected, since the `abc' at the end of `something1234abc' should not normally match `[A-Z]*'. This result is due to the locale setting (and thus you may not see it on your system). There are two fixes. The first is to use the POSIX character class `[[:upper:]]', instead of `[A-Z]'. The second is to change the locale setting in the environment, before running `gawk', by using the shell statements: LANG=C LC_ALL=C export LANG LC_ALL The setting `C' forces `gawk' to behave in the traditional Unix manner, where case distinctions do matter. You may wish to put these statements into your shell startup file, e.g., `$HOME/.profile'. Similar considerations apply to other ranges. For example, `["-/]' is perfectly valid in ASCII, but is not valid in many Unicode locales, such as `en_US.UTF-8'. (In general, such ranges should be avoided; either list the characters individually, or use a POSIX character class such as `[[:punct:]]'.) For the normal case of `RS = "\n"', the locale is largely irrelevant. For other single byte record separators, using `LC_ALL=C' will give you much better performance when reading records. Otherwise, `gawk' has to make several function calls, _per input character_ to find the record terminator.  File: gawk.info, Node: Reading Files, Next: Printing, Prev: Regexp, Up: Top d2259 6 a2264 6 standard input (by default, this is the keyboard, but often it is a pipe from another command) or from files whose names you specify on the `awk' command line. If you specify input files, `awk' reads them in order, processing all the data from one before going on to the next. The name of the current input file can be found in the built-in variable `FILENAME' (*note Built-in Variables::). d2266 1 a2266 1 The input is read in units called "records", and is processed by the d2272 1 a2272 1 On rare occasions, you may need to use the `getline' command. The d2275 2 a2276 1 have to be named on the `awk' command line (*note Getline::). d2282 1 a2282 1 * Nonconstant Fields:: Nonconstant Field Numbers. d2291 1 a2291 1 File: gawk.info, Node: Records, Next: Fields, Up: Reading Files d2293 1 a2293 1 How Input Is Split into Records d2297 15 a2311 21 records and fields. `awk' keeps track of the number of records that have been read so far from the current input file. This value is stored in a built-in variable called `FNR'. It is reset to zero when a new file is started. Another built-in variable, `NR', is the total number of input records read so far from all data files. It starts at zero, but is never automatically reset to zero. Records are separated by a character called the "record separator". By default, the record separator is the newline character. This is why records are, by default, single lines. A different character can be used for the record separator by assigning the character to the built-in variable `RS'. Like any other variable, the value of `RS' can be changed in the `awk' program with the assignment operator, `=' (*note Assignment Ops::). The new record-separator character should be enclosed in quotation marks, which indicate a string constant. Often the right time to do this is at the beginning of execution, before any input is processed, so that the very first record is read with the proper separator. To do this, use the special `BEGIN' pattern (*note BEGIN/END::). For example: d2313 1 a2313 2 awk 'BEGIN { RS = "/" } { print $0 }' BBS-list d2319 4 a2322 3 Because each `print' statement adds a newline at the end of its output, this `awk' program copies the input with each slash changed to a newline. Here are the results of running the program on `BBS-list': d2324 1 a2324 2 $ awk 'BEGIN { RS = "/" } > { print $0 }' BBS-list d2353 2 a2354 2 original data file (*note Sample Data Files::), the line looks like this: d2358 1 a2358 5 It has one baud rate only, so there are no slashes in the record, unlike the others which have two or more baud rates. In fact, this record is treated as part of the record for the `core' BBS; the newline separating them in the output is the original newline in the data file, not the one added by `awk' when it printed the record! d2361 2 a2362 1 using the variable-assignment feature (*note Other Arguments::): d2370 3 a2372 1 following (extreme) pipeline prints a surprising `1': d2377 8 a2384 11 There is one field, consisting of a newline. The value of the built-in variable `NF' is the number of fields in the current record. Reaching the end of an input file terminates the current input record, even if the last character in the file is not the character in `RS'. (d.c.) The empty string `""' (a string without any characters) has a special meaning as the value of `RS'. It means that records are separated by one or more blank lines and nothing else. *Note Multiple Line::, for more details. d2388 1 a2388 1 currently being processed, as well as records already processed, are not d2392 17 a2408 14 variable `RT' to the text in the input that matched `RS'. When using `gawk', the value of `RS' is not limited to a one-character string. It can be any regular expression (*note Regexp::). In general, each record ends at the next string that matches the regular expression; the next record starts at the end of the matching string. This general rule is actually at work in the usual case, where `RS' contains just a newline: a record ends at the beginning of the next matching string (the next newline in the input), and the following record starts just after the end of this string (at the first character of the following line). The newline, because it matches `RS', is not part of either record. When `RS' is a single character, `RT' contains the same single character. However, when `RS' is a regular expression, `RT' contains the actual input text that matched the regular expression. d2411 3 a2413 3 `RS' equal to a regular expression that matches either a newline or a series of one or more uppercase letters with optional leading and/or trailing whitespace: d2424 5 a2428 11 value of `RT' is a newline, and the `print' statement supplies its own terminating newline. *Note Simple Sed::, for a more useful example of `RS' as a regexp and `RT'. If you set `RS' to a regular expression that allows optional trailing text, such as `RS = "abc(XYZ)?"' it is possible, due to implementation constraints, that `gawk' may match the leading part of the regular expression, but not the trailing part, particularly if the input text that could match the trailing part is fairly long. `gawk' attempts to avoid this problem, but currently, there's no guarantee that this will never happen. d2432 3 a2434 32 Options::). In compatibility mode, only the first character of the value of `RS' is used to determine the end of the record. Advanced Notes: `RS = "\0"' Is Not Portable ------------------------------------------- There are times when you might want to treat an entire data file as a single record. The only way to make this happen is to give `RS' a value that you know doesn't occur in the input file. This is hard to do in a general way, such that a program always works for arbitrary input files. You might think that for text files, the NUL character, which consists of a character with all bits equal to zero, is a good value to use for `RS' in this case: BEGIN { RS = "\0" } # whole file becomes one record? `gawk' in fact accepts this, and uses the NUL character for the record separator. However, this usage is _not_ portable to other `awk' implementations. All other `awk' implementations(1) store strings internally as C-style strings. C strings use the NUL character as the string terminator. In effect, this means that `RS = "\0"' is the same as `RS = ""'. (d.c.) The best way to treat a whole file as a single record is to simply read the file in, one record at a time, concatenating each record onto the end of the previous ones. ---------- Footnotes ---------- d2436 6 a2441 1 (1) At least that we know about. d2444 1 a2444 1 File: gawk.info, Node: Fields, Next: Nonconstant Fields, Prev: Records, Up: Reading Files d2450 5 a2454 5 "parsed" or separated by the interpreter into chunks called "fields". By default, fields are separated by "whitespace", like words in a line. Whitespace in `awk' means any string of one or more spaces, tabs, or newlines;(1) other characters, such as formfeed, vertical tab, etc. that are considered whitespace by other languages, are _not_ considered d2459 1 a2459 1 operate on the whole record if you want--but fields are what make d2462 1 a2462 1 A dollar-sign (`$') is used to refer to a field in an `awk' program, d2464 1 a2464 3 first field, `$2' to the second, and so on. (Unlike the Unix shells, the field numbers are not limited to single digits. `$127' is the one hundred twenty-seventh field in the record.) For example, suppose the d2469 2 a2470 2 Here the first field, or `$1', is `This', the second field, or `$2', is `seems', and so on. Note that the last field, `$7', is `example.'. d2475 15 a2489 10 the current record. `awk' automatically updates the value of `NF' each time it reads a record. No matter how many fields there are, the last field in a record can be represented by `$NF'. So, `$NF' is the same as `$7', which is `example.'. If you try to reference a field beyond the last one (such as `$8' when the record has only seven fields), you get the empty string. (If used in a numeric operation, you get zero.) The use of `$0', which looks like a reference to the "zero-th" field, is a special case: it represents the whole input record when you are not interested in specific fields. Here are some more examples: d2499 7 a2505 6 "matching operator" (*note Regexp Usage::); it tests whether a string (here, the field `$1') matches a given regular expression. By contrast, the following example looks for `foo' in _the entire record_ and prints the first field and the last field for each matching input record: d2515 1 a2515 1 (1) In POSIX `awk', newlines are not considered whitespace for d2519 1 a2519 1 File: gawk.info, Node: Nonconstant Fields, Next: Changing Fields, Prev: Fields, Up: Reading Files d2521 2 a2522 2 Nonconstant Field Numbers ========================= d2536 3 a2538 2 record has fewer than 20 fields, so this prints a blank line. Here is another example of using expressions as field numbers: d2542 1 a2542 1 `awk' evaluates the expression `(2*2)' and uses its value as the d2550 1 a2550 1 Precedence::.) d2554 11 a2564 10 not allowed; trying to reference one usually terminates the program. (The POSIX standard does not define what happens when you reference a negative field number. `gawk' notices this and terminates your program. Other `awk' implementations may behave differently.) As mentioned in *Note Fields::, `awk' stores the current record's number of fields in the built-in variable `NF' (also *note Built-in Variables::). The expression `$NF' is not a special feature--it is the direct consequence of evaluating `NF' and using its value as a field number. d2567 1 a2567 1 File: gawk.info, Node: Changing Fields, Next: Field Separators, Prev: Nonconstant Fields, Up: Reading Files d2572 1 a2572 1 The contents of a field, as seen by `awk', can be changed within an d2574 4 a2577 2 record. (The actual input is untouched; `awk' _never_ modifies the input file.) Consider the following example and its output: d2579 4 a2582 5 $ awk '{ nboxes = $3 ; $3 = $3 - 10 > print nboxes, $3 }' inventory-shipped -| 25 15 -| 32 22 -| 24 14 d2585 11 a2595 12 The program first saves the original value of field three in the variable `nboxes'. The `-' sign represents subtraction, so this program reassigns field three, `$3', as the original value of field three minus ten: `$3 - 10'. (*Note Arithmetic Ops::.) Then it prints the original and new values for field three. (Someone in the warehouse made a consistent mistake while inventorying the red boxes.) For this to work, the text in field `$3' must make sense as a number; the string of characters must be converted to a number for the computer to do arithmetic on it. The number resulting from the subtraction is converted back to a string of characters that then becomes field three. *Note Conversion::. d2597 1 a2597 1 When the value of a field is changed (as perceived by `awk'), the d2599 3 a2601 3 the old one was. In other words, `$0' changes to reflect the altered field. Thus, this program prints a copy of the input file, with 10 subtracted from the second field of each line: d2609 2 a2610 2 It is also possible to also assign contents to fields that are out of range. For example: d2625 3 a2627 3 input record, which is the value of `$0'. Thus, if you do `print $0' after adding a field, the record printed includes the new field, with the appropriate number of field separators between it and the previously d2631 4 a2634 5 fields; *note Fields::). For example, the value of `NF' is set to the number of the highest field you create. The exact format of `$0' is also affected by a feature that has not been discussed yet: the "output field separator", `OFS', used to separate the fields (*note Output Separators::). d2636 2 a2637 2 Note, however, that merely _referencing_ an out-of-range field does _not_ change the value of either `$0' or `NF'. Referencing an d2646 4 a2649 3 out of range. (*Note If Statement::, for more information about `awk''s `if-else' statements. *Note Typing and Comparison::, for more information about the `!=' operator.) d2652 2 a2653 2 field changes the value of `$0' but does not change the value of `NF', even when you assign the empty string to a field. For example: d2660 4 a2663 3 The field is still there; it just has an empty value, denoted by the two colons between `a' and `c'. This example shows what happens if you create a new field: d2670 1 a2670 1 The intervening field, `$5', is created with an empty value (indicated d2674 2 a2675 2 Decrementing `NF' throws away the values of the fields after the new value of `NF' and recomputes `$0'. (d.c.) Here is an example: d2677 2 a2678 2 $ echo a b c d e f | awk '{ print "NF =", NF; > NF = 3; print $0 }' a2681 19 *Caution:* Some versions of `awk' don't rebuild `$0' when `NF' is decremented. Caveat emptor. Finally, there are times when it is convenient to force `awk' to rebuild the entire record, using the current value of the fields and `OFS'. To do this, use the seemingly innocuous assignment: $1 = $1 # force record to be reconstituted print $0 # or whatever else with $0 This forces `awk' rebuild the record. It does help to add a comment, as we've shown here. There is a flip side to the relationship between `$0' and the fields. Any assignment to `$0' causes the record to be reparsed into fields using the _current_ value of `FS'. This also applies to any built-in function that updates `$0', such as `sub' and `gsub' (*note String Functions::). d2685 1 a2685 1 Specifying How Fields Are Separated d2688 3 d2693 2 d2697 1 a2697 1 * Command Line Field Separator:: Setting `FS' from the command-line. d2700 6 d2712 4 a2715 3 In the examples that follow, we use the bullet symbol (*) to represent spaces in the output. If the field separator is `oo', then the following line: d2719 1 a2719 1 is split into three fields: `m', `*g', and `*gai*pan'. Note the d2723 11 a2733 10 Shell programmers take note: `awk' does _not_ use the name `IFS' that is used by the POSIX-compliant shells (such as the Unix Bourne shell, `sh', or `bash'). The value of `FS' can be changed in the `awk' program with the assignment operator, `=' (*note Assignment Ops::). Often the right time to do this is at the beginning of execution before any input has been processed, so that the very first record is read with the proper separator. To do this, use the special `BEGIN' pattern (*note BEGIN/END::). For example, here we set the value of `FS' to the string d2738 1 a2738 1 Given the input line: d2744 2 a2745 2 Sometimes the input data contains separator characters that don't separate fields the way you thought they would. For instance, the d2747 2 a2748 1 attached, such as: d2752 1 a2752 1 The same program would extract `*LXIX', instead of `*29*Oak*St.'. If d2754 8 a2761 10 surprised. The moral is to choose your data layout and separator characters carefully to prevent such problems. (If the data is not in a form that is easy to process, perhaps you can massage it first with a separate `awk' program.) Fields are normally separated by whitespace sequences (spaces, tabs, and newlines), not by single spaces. Two spaces in a row do not delimit an empty field. The default value of the field separator `FS' is a string containing a single space, `" "'. If `awk' interpreted this value in the usual way, each space character would separate d2764 1 a2764 1 `FS' is a special case--it is taken to specify the default manner of d2771 1 a2771 1 space character is the only single character that does not follow these d2775 1 a2775 1 File: gawk.info, Node: Regexp Field Splitting, Next: Single Character Fields, Up: Field Separators d2789 2 a2790 2 space and a TAB into a field separator. (`\t' is an "escape sequence" that stands for a TAB; *note Escape Sequences::, for the complete list d2793 5 a2797 4 For a less trivial example of a regular expression, try using single spaces to separate fields the way single commas are used. `FS' can be set to `"[ ]"' (left bracket, space, right bracket). This regular expression matches a single space and nothing else (*note Regexp::). d2800 9 a2808 7 (a single space) and `FS = "[ \t\n]+"' (a regular expression matching one or more spaces, tabs, or newlines). For both values of `FS', fields are separated by "runs" (multiple adjacent occurrences) of spaces, tabs, and/or newlines. However, when the value of `FS' is `" "', `awk' first strips leading and trailing whitespace from the record and then decides where the fields are. For example, the following pipeline prints `b': d2816 1 a2816 1 $ echo ' a b c d ' | awk 'BEGIN { FS = "[ \t\n]+" } d2820 1 a2820 1 In this case, the first field is "null" or empty. d2832 2 a2833 2 `OFS'. Because the leading whitespace was ignored when finding `$1', it is not part of the new `$0'. Finally, the last `print' statement d2843 3 a2845 3 record separately. This can be done in `gawk' by simply assigning the null string (`""') to `FS'. In this case, each individual character in the record becomes a separate field. For example: d2856 5 a2860 5 Traditionally, the behavior of `FS' equal to `""' was not defined. In this case, most versions of Unix `awk' simply treat the entire record as only having one field. (d.c.) In compatibility mode (*note Options::), if `FS' is the null string, then `gawk' also behaves this way. d2868 2 a2869 2 `FS' can be set on the command line. Use the `-F' option to do so. For example: d2873 6 a2878 6 sets `FS' to the `,' character. Notice that the option uses an uppercase `F' instead of a lowercase `f'. The latter option (`-f') specifies a file containing an `awk' program. Case is significant in command-line options: the `-F' and `-f' options have nothing to do with each other. You can use both options at the same time to set the `FS' variable _and_ get an `awk' program from a file. d2881 3 a2883 3 same way as assignments to the built-in variable `FS'. Any special characters in the field separator must be escaped appropriately. For example, to use a `\' as the field separator on the command line, you d2889 3 a2891 3 Because `\' is used for quoting in the shell, `awk' sees `-F\\'. Then `awk' processes the `\\' for escape characters (*note Escape Sequences::), finally yielding a single `\' to use for the field d2894 7 a2900 6 As a special case, in compatibility mode (*note Options::), if the argument to `-F' is `t', then `FS' is set to the TAB character. If you type `-F\t' at the shell, without any quotes, the `\' gets deleted, so `awk' figures that you really want your fields to be separated with tabs and not `t's. Use `-v FS="t"' or `-F"[t]"' on the command line if you really do want to separate your fields with `t's. d2903 2 a2904 1 contains the pattern `/300/' and the action `print $1': d2908 1 a2908 1 Let's also set `FS' to be the `-' character and run the program on d2917 1 a2917 8 -| bites 555 -| camelot 555 -| core 555 -| fooey 555 -| foot 555 -| macfoo 555 -| sdace 555 -| sabafoo 555 d2919 2 a2920 2 Note the second line of output. The second line in the original file looked like this: d2929 4 a2932 6 Perhaps the most common use of a single character as the field separator occurs when processing the Unix system password file. On many Unix systems, each user has a separate entry in the system password file, one line per user. The information in these lines is separated by colons. The first field is the user's logon name and the second is the user's (encrypted or shadow) password. A password file entry might d2935 1 a2935 1 arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash d2937 1 a2937 1 The following program searches the system password file and prints d2945 1 a2945 1 Field-Splitting Summary d2948 23 a2970 8 It is important to remember that when you assign a string constant as the value of `FS', it undergoes normal `awk' string processing. For example, with Unix `awk' and `gawk', the assignment `FS = "\.."' assigns the character string `".."' to `FS' (the backslash is stripped). This creates a regexp meaning "fields are separated by occurrences of any two characters." If instead you want fields to be separated by a literal period followed by any single character, use `FS = "\\.."'. d2973 1 a2973 1 value of `FS' (`==' means "is equal to"): a2991 47 (This is a `gawk' extension; it is not specified by the POSIX standard.) Advanced Notes: Changing `FS' Does Not Affect the Fields -------------------------------------------------------- According to the POSIX standard, `awk' is supposed to behave as if each record is split into fields at the time it is read. In particular, this means that if you change the value of `FS' after a record is read, the value of the fields (i.e., how they were split) should reflect the old value of `FS', not the new one. However, many implementations of `awk' do not work this way. Instead, they defer splitting the fields until a field is actually referenced. The fields are split using the _current_ value of `FS'! (d.c.) This behavior can be difficult to diagnose. The following example illustrates the difference between the two methods. (The `sed'(1) command prints just the first line of `/etc/passwd'.) sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }' which usually prints: root on an incorrect implementation of `awk', while `gawk' prints something like: root:nSijPlPhZZwgE:0:0:Root:/: Advanced Notes: `FS' and `IGNORECASE' ------------------------------------- The `IGNORECASE' variable (*note User-modified::) affects field splitting _only_ when the value of `FS' is a regexp. It has no effect when `FS' is a single character, even if that character is a letter. Thus, in the following code: FS = "c" IGNORECASE = 1 $0 = "aCa" print $1 The output is `aCa'. If you really want to split fields on an alphabetic character while ignoring case, use a regexp that will do it for you. E.g., `FS = "[c]"'. In this case, `IGNORECASE' will take effect. d2995 1 a2995 1 (1) The `sed' utility is a "stream editor." Its behavior is also d3001 1 a3001 1 Reading Fixed-Width Data d3004 2 a3005 2 (This minor node discusses an advanced feature of `awk'. If you are a novice `awk' user, you might want to skip it on the first reading.) d3007 4 a3010 4 `gawk' version 2.13 introduced a facility for dealing with fixed-width fields with no distinctive field separator. For example, data of this nature arises in the input for old Fortran programs where numbers are run together, or in the output of programs that did not d3014 2 a3015 2 up by the use of a variable number of spaces and _empty fields are just spaces_. Clearly, `awk''s normal field splitting based on `FS' does d3017 3 a3019 2 a series of `substr' calls on `$0' (*note String Functions::), this is awkward and inefficient for a large number of fields. d3024 6 a3029 6 of the field, _including_ columns between fields. If you want to ignore the columns between fields, you can specify the width as a separate field that is subsequently ignored. It is a fatal error to supply a field width that is not a positive number. The following data is the output of the Unix `w' utility. It is useful to illustrate the use of `FIELDWIDTHS': d3043 3 a3045 5 to number of seconds, and prints out the first two fields and the calculated idle time: *Note:* This program uses a number of `awk' features that haven't been introduced yet. d3063 1 a3063 1 Running the program on the data produces the following results: d3075 4 a3078 4 is the input from a deck of balloting cards. In some parts of the United States, voters mark their choices by punching holes in computer cards. These cards are then processed to count the votes for any particular candidate or on any particular issue. Because a voter may d3084 7 a3090 16 Assigning a value to `FS' causes `gawk' to use `FS' for field splitting again. Use `FS = FS' to make this happen, without having to know the current value of `FS'. In order to tell which kind of field splitting is in effect, use `PROCINFO["FS"]' (*note Auto-set::). The value is `"FS"' if regular field splitting is being used, or it is `"FIELDWIDTHS"' if fixed-width field splitting is being used: if (PROCINFO["FS"] == "FS") REGULAR FIELD SPLITTING ... else FIXED-WIDTH FIELD SPLITTING ... This information is useful when writing a function that needs to temporarily change `FS' or `FIELDWIDTHS', read some records, and then restore the original settings (*note Passwd Functions::, for an example of such a function). d3098 7 a3104 3 In some databases, a single line cannot conveniently hold all the information in one entry. In such cases, you can use multiline records. The first step in doing this is to choose your data format. d3115 5 a3119 6 that records are separated by one or more blank lines. When `RS' is set to the empty string, each record always ends at the first blank line encountered. The next record doesn't start until the first nonblank line that follows. No matter how many blank lines appear in a row, they all act as one record separator. (Blank lines must be completely empty; lines that contain only whitespace do not count.) d3123 1 a3123 1 record and one or more blank lines after the record. In addition, a d3125 4 a3128 4 there is a choice (*note Leftmost Longest::). So the next record doesn't start until the first nonblank line that follows--no matter how many blank lines appear in a row, they are considered one record separator. d3134 1 a3134 1 second case, this special processing is not done. (d.c.) d3139 3 a3141 4 as the result of a special feature. When `RS' is set to the empty string, _and_ `FS' is a set to a single character, the newline character _always_ acts as a field separator. This is in addition to whatever field separations result from `FS'.(1) d3144 1 a3144 1 provide useful behavior in the default case (i.e., `FS' is equal to d3146 4 a3149 7 newline character to separate fields, because there is no way to prevent it. However, you can work around this by using the `split' function to break up the record manually (*note String Functions::). If you have a single character field separator, you can work around the special feature in a different way, by making `FS' into a regexp for that single character. For example, if the field separator is a percent character, instead of `FS = "%"', use `FS = "[%]"'. d3153 5 a3157 4 (This single character seperator matches a single newline.) A practical example of a data file organized this way might be a mailing list, where each entry is separated by blank lines. Consider a mailing list in a file named `addresses', which looks like this: d3166 1 d3169 1 a3169 1 A simple program to process this file is as follows: d3197 5 a3201 3 *Note Labels Program::, for a more realistic program that deals with address lists. The following table summarizes how records are split, based on the value of `RS'. (`==' means "is equal to.") d3221 1 a3221 2 records. (This is a `gawk' extension; it is not specified by the POSIX standard.) a3225 6 ---------- Footnotes ---------- (1) When `FS' is the null string (`""') or a regexp, this special feature of `RS' does not apply. It does apply to the default field separator of a single space: `FS = " "'. d3238 31 a3268 12 The `getline' command is used in several different ways and should _not_ be used by beginners. The examples that follow the explanation of the `getline' command include material that has not been covered yet. Therefore, come back and study the `getline' command _after_ you have reviewed the rest of this Info file and have a good knowledge of how `awk' works. The `getline' command returns one if it finds a record and zero if it encounters the end of the file. If there is some error in getting a record, such as a file that cannot be opened, then `getline' returns -1. In this case, `gawk' sets the variable `ERRNO' to a string describing the error that occurred. a3272 16 * Menu: * Plain Getline:: Using `getline' with no arguments. * Getline/Variable:: Using `getline' into a variable. * Getline/File:: Using `getline' from a file. * Getline/Variable/File:: Using `getline' into a variable from a file. * Getline/Pipe:: Using `getline' from a pipe. * Getline/Variable/Pipe:: Using `getline' into a variable from a pipe. * Getline/Coprocess:: Using `getline' from a coprocess. * Getline/Variable/Coprocess:: Using `getline' into a variable from a coprocess. * Getline Notes:: Important things to know about `getline'. * Getline Summary:: Summary of `getline' Variants. d3274 1 a3274 1 File: gawk.info, Node: Plain Getline, Next: Getline/Variable, Up: Getline d3282 2 a3283 2 finished processing the current record, but want to do some special processing on the next record _right now_. For example: d3285 1 a3285 1 { d3287 1 a3287 1 # value of `tmp' will be "" if t is 1 d3302 1 a3302 1 $0 = tmp substr($0, u + 2) d3305 1 a3305 1 } d3307 1 a3307 1 This `awk' program deletes all C-style comments (`/* ... */') from d3310 8 a3317 3 such as searching for matches of a regular expression. (This program has a subtle problem--it does not work if one comment ends and another begins on the same line.) d3319 1 a3319 4 This form of the `getline' command sets `NF', `NR', `FNR', and the value of `$0'. *Note:* The new value of `$0' is used to test the patterns of any d3321 4 a3324 3 that executed `getline' is lost. By contrast, the `next' statement reads a new record but immediately begins processing it normally, starting with the first rule in the program. *Note Next Statement::. d3329 1 a3329 1 Using `getline' into a Variable d3333 1 a3333 6 into the variable VAR. No other processing is done. For example, suppose the next line is a comment or a special string, and you want to read it without triggering any rules. This form of `getline' allows you to read that line and store it in a variable so that the main read-a-line-and-check-each-rule loop of `awk' never sees it. The following example swaps every two lines of input: d3335 5 a3339 7 { if ((getline tmp) > 0) { print tmp print $0 } else print $0 } d3341 2 a3342 1 It takes the following list: d3349 1 a3349 1 and produces these results: d3356 10 d3377 8 a3384 6 Use `getline < FILE' to read the next record from FILE. Here FILE is a string-valued expression that specifies the file name. `< FILE' is called a "redirection" because it directs input to come from a different place. For example, the following program reads its input record from the file `secondary.input' when it encounters a first field with a value equal to 10 in the current input file: d3386 1 a3386 1 { d3392 1 a3392 1 } d3394 4 a3397 4 Because the main input stream is not used, the values of `NR' and `FNR' are not changed. However, the record it reads is split into fields in the normal manner, so the values of `$0' and the other fields are changed, resulting in a new value of `NF'. d3402 1 a3402 1 concatenation operator is not parenthesized. You should write it as d3409 1 a3409 1 Using `getline' into a Variable from a File d3412 3 a3414 3 Use `getline VAR < FILE' to read input from the file FILE, and put it in the variable VAR. As above, FILE is a string-valued expression that specifies the file from which to read. d3417 13 a3429 5 changed and the record is not split into fields. The only variable changed is VAR. For example, the following program copies all the input files to the output, except for records that say `@@include FILENAME'. Such a record is replaced by the contents of the file FILENAME: d3431 1 a3431 1 { d3438 1 a3438 1 } d3441 2 a3442 2 program; it is taken directly from the data, specifically from the second field on the `@@include' line. d3446 2 a3447 1 included twice. *Note Close Files And Pipes::. d3450 4 a3453 3 `@@include' statements (i.e., `@@include' statements in included files) the way a true macro preprocessor would. *Note Igawk Program::, for a program that does handle nested `@@include' statements. d3461 8 a3468 7 The output of a command can also be piped into `getline', using `COMMAND | getline'. In this case, the string COMMAND is run as a shell command and its output is piped into `awk' to be used as input. This form of `getline' reads one record at a time from the pipe. For example, the following program copies its input to its output, except for lines that begin with `@@execute', which are replaced by the output produced by running the rest of the line as a shell command: d3470 1 a3470 1 { d3478 1 a3478 1 } d3482 3 a3484 1 *Note Close Files And Pipes::. Given the input: d3502 3 a3504 3 Notice that this program ran the command `who' and printed the previous result. (If you try this program yourself, you will of course get different results, depending upon who is logged in on your system.) d3507 2 a3508 2 value of `NF', and recomputes the value of `$0'. The values of `NR' and `FNR' are not changed. d3511 1 a3511 1 EXPRESSION contains unparenthesized operators other than `$'--for d3513 1 a3513 1 concatenation operator is not parenthesized. You should write it as d3518 1 a3518 1 File: gawk.info, Node: Getline/Variable/Pipe, Next: Getline/Coprocess, Prev: Getline/Pipe, Up: Getline d3520 1 a3520 1 Using `getline' into a Variable from a Pipe d3523 5 a3527 4 When you use `COMMAND | getline VAR', the output of COMMAND is sent through a pipe to `getline' and into the variable VAR. For example, the following program reads the current date and time into the variable `current_time', using the `date' utility, and then prints it: d3529 1 a3529 1 BEGIN { d3533 1 a3533 1 } d3536 1 a3536 1 changed and the record is not split into fields. d3541 1 a3541 1 concatenation operator is not parenthesized. You should write it as d3546 1 a3546 1 File: gawk.info, Node: Getline/Coprocess, Next: Getline/Variable/Coprocess, Prev: Getline/Variable/Pipe, Up: Getline d3548 2 a3549 2 Using `getline' from a Coprocess -------------------------------- d3551 19 a3569 3 Input into `getline' from a pipe is a one-way operation. The command that is started with `COMMAND | getline' only sends data _to_ your `awk' program. d3571 2 a3572 29 On occasion, you might want to send data to another program for processing and then read the results back. `gawk' allows you start a "coprocess", with which two-way communications are possible. This is done with the `|&' operator. Typically, you write data to the coprocess first and then read results back, as shown in the following: print "SOME QUERY" |& "db_server" "db_server" |& getline which sends a query to `db_server' and then reads the results. The values of `NR' and `FNR' are not changed, because the main input stream is not used. However, the record is split into fields in the normal manner, thus changing the values of `$0', of the other fields, and of `NF'. Coprocesses are an advanced feature. They are discussed here only because this is the minor node on `getline'. *Note Two-way I/O::, where coprocesses are discussed in more detail.  File: gawk.info, Node: Getline/Variable/Coprocess, Next: Getline Notes, Prev: Getline/Coprocess, Up: Getline Using `getline' into a Variable from a Coprocess ------------------------------------------------ When you use `COMMAND |& getline VAR', the output from the coprocess COMMAND is sent through a two-way pipe to `getline' and into the variable VAR. d3574 2 a3575 16 In this version of `getline', none of the built-in variables are changed and the record is not split into fields. The only variable changed is VAR. Coprocesses are an advanced feature. They are discussed here only because this is the minor node on `getline'. *Note Two-way I/O::, where coprocesses are discussed in more detail.  File: gawk.info, Node: Getline Notes, Next: Getline Summary, Prev: Getline/Variable/Coprocess, Up: Getline Points to Remember About `getline' ---------------------------------- Here are some miscellaneous points about `getline' that you should bear in mind: d3577 2 a3578 24 * When `getline' changes the value of `$0' and `NF', `awk' does _not_ automatically jump to the start of the program and start testing the new record against every pattern. However, the new record is tested against any subsequent rules. * Many `awk' implementations limit the number of pipelines that an `awk' program may have open to just one. In `gawk', there is no such limit. You can open as many pipelines (and coprocesses) as the underlying operating system permits. * An interesting side effect occurs if you use `getline' without a redirection inside a `BEGIN' rule. Because an unredirected `getline' reads from the command-line data files, the first `getline' command causes `awk' to set the value of `FILENAME'. Normally, `FILENAME' does not have a value inside `BEGIN' rules, because you have not yet started to process the command-line data files. (d.c.) (*Note BEGIN/END::, also *note Auto-set::.) * Using `FILENAME' with `getline' (`getline < FILENAME') is likely to be a source for confusion. `awk' opens a separate input stream from the current input file. However, by not using a variable, `$0' and `NR' are still updated. If you're doing this, it's probably by accident, and you should reconsider what it is you're trying to accomplish. d3580 2 a3581 2  File: gawk.info, Node: Getline Summary, Prev: Getline Notes, Up: Getline d3583 2 a3584 2 Summary of `getline' Variants ----------------------------- d3586 2 a3587 2 The following table summarizes the eight variants of `getline', listing which built-in variables are set by each one. d3589 2 a3590 9 `getline' Sets `$0', `NF', `FNR', and `NR' `getline' VAR Sets VAR, `FNR', and `NR' `getline <' FILE Sets `$0' and `NF' `getline VAR < FILE' Sets VAR COMMAND `| getline' Sets `$0' and `NF' COMMAND `| getline' VAR Sets VAR COMMAND `|& getline' Sets `$0' and `NF'. This is a `gawk' extension COMMAND `|& getline' VAR Sets VAR. This is a `gawk' extension d3598 4 a3601 14 One of the most common programming actions is to "print", or output, some or all of the input. Use the `print' statement for simple output, and the `printf' statement for fancier formatting. The `print' statement is not limited when computing _which_ values to print. However, with two exceptions, you cannot specify _how_ to print them--how many columns, whether to use exponential notation or not, and so on. (For the exceptions, *note Output Separators::, and *Note OFMT::.) For printing with specifications, you need the `printf' statement (*note Printf::). Besides basic and formatted printing, this major node also covers I/O redirections to files and pipes, introduces the special file names that `gawk' processes internally, and discusses the `close' built-in function. d3618 1 a3618 1 File: gawk.info, Node: Print, Next: Print Examples, Up: Printing d3623 4 a3626 4 The `print' statement is used to produce output with simple, standardized formatting. Specify only the strings or numbers to print, in a list separated by commas. They are output, separated by single spaces, followed by a newline. The statement looks like this: d3630 1 a3630 1 The entire list of items may be optionally enclosed in parentheses. The d3633 1 a3633 1 (*note Redirection::). d3635 11 a3645 3 The items to print can be constant strings or numbers, fields of the current record (such as `$1'), variables, or any `awk' expression. Numeric values are converted to strings and then printed. d3649 12 a3660 5 `print ""', where `""' is the empty string. To print a fixed piece of text, use a string constant, such as `"Don't Panic"', as one item. If you forget to use the double-quote characters, your text is taken as an `awk' expression, and you will probably get an error. Keep in mind that a space is printed between any two items. d3668 3 a3670 9 Each `print' statement makes at least one line of output. However, it isn't limited to only one line. If an item value is a string that contains a newline, the newline is output along with the rest of the string. A single `print' statement can make any number of lines this way. The following is an example of printing a string that contains embedded newlines (the `\n' is an escape sequence, used to represent the newline character; *note Escape Sequences::): d3677 2 a3678 3 The next example, which is run on the `inventory-shipped' file, prints the first two fields of each input record, with a space between them: d3698 1 a3698 1 To someone unfamiliar with the `inventory-shipped' file, neither d3702 2 a3703 1 pattern (*note BEGIN/END::) so that the headings are only printed once: d3709 2 a3710 1 When run, the program prints the following: d3719 2 a3720 3 The only problem, however, is that the headings and the table data don't line up! We can fix this by printing some spaces between the two fields: d3726 5 a3730 4 Lining up columns this way can get pretty complicated when there are many columns to fix. Counting spaces for two or three columns is simple, but any more than this can take up a lot of time. This is why the `printf' statement was created (*note Printf::); one of its d3733 3 a3735 2 *Note:* You can continue either a `print' or `printf' statement simply by putting a newline after any comma (*note Statements/Lines::). d3744 6 a3749 6 items separated by commas. In the output, the items are normally separated by single spaces. However, this doesn't need to be the case; a single space is only the default. Any string of characters may be used as the "output field separator" by setting the built-in variable `OFS'. The initial value of this variable is the string `" "'--that is, a single space. d3752 17 a3768 13 record". Each `print' statement outputs one output record, and then outputs a string called the "output record separator" (or `ORS'). The initial value of `ORS' is the string `"\n"'; i.e., a newline character. Thus, each `print' statement normally makes a separate line. In order to change how output fields and records are separated, assign new values to the variables `OFS' and `ORS'. The usual place to do this is in the `BEGIN' rule (*note BEGIN/END::), so that it happens before any input is processed. It can also be done with assignments on the command line, before the names of the input files, or using the `-v' command-line option (*note Options::). The following example prints the first and second fields of each input record, separated by a semicolon, with a blank line added after each newline: d3779 3 a3781 2 If the value of `ORS' does not contain a newline, the program's output is run together on a single line. d3789 2 a3790 2 When the `print' statement is used to print numeric values, `awk' internally converts the number to a string of characters and prints d3792 6 a3797 5 (*note String Functions::). For now, it suffices to say that the `sprintf' function accepts a "format specification" that tells it how to format numbers (or strings), and that there are a number of different ways in which numbers can be formatted. The different format specifications are discussed more fully in *Note Control Letters::. d3802 3 a3804 3 `"%.6g"'. The way `print' prints numbers can be changed by supplying different format specifications as the value of `OFMT', as shown in the following example: d3808 2 a3809 2 > print 17.23, 17.54 }' -| 17 18 d3811 3 a3813 3 According to the POSIX standard, `awk''s behavior is undefined if `OFMT' contains anything but a floating-point conversion specification. (d.c.) d3821 7 a3827 8 For more precise control over the output format than what is normally provided by `print', use `printf'. `printf' can be used to specify the width to use for each item, as well as various formatting choices for numbers (such as what output base to use, whether to print an exponent, whether to print a sign, and how many digits to print after the decimal point). This is done by supplying a string, called the "format string", that controls how and where to print the other arguments. d3837 1 a3837 1 File: gawk.info, Node: Basic Printf, Next: Control Letters, Up: Printf d3842 1 a3842 1 A simple `printf' statement looks like this: d3848 3 a3850 2 `>' relational operator; otherwise, it can be confused with a redirection (*note Redirection::). d3857 3 a3859 3 The format string is very similar to that in the ISO C library function `printf'. Most of FORMAT is text to output verbatim. Scattered among this text are "format specifiers"--one per item. Each d3863 4 a3866 4 The `printf' statement does not automatically append a newline to its output. It outputs only what the format string specifies. So if a newline is needed, you must include one in the format string. The output separator variables `OFS' and `ORS' have no effect on `printf' d3869 4 a3872 6 $ awk 'BEGIN { > ORS = "\nOUCH!\n"; OFS = "+" > msg = "Dont Panic!" > printf "%s\n", msg > }' -| Dont Panic! d3874 1 a3874 1 Here, neither the `+' nor the `OUCH' appear when the message is printed. d3883 22 a3904 18 "format-control letter"--it tells the `printf' statement how to output one item. The format-control letter specifies what _kind_ of value to print. The rest of the format specifier is made up of optional "modifiers" that control _how_ to print the value, such as the field width. Here is a list of the format-control letters: `%c' This prints a number as an ASCII character; thus, `printf "%c", 65' outputs the letter `A'. (The output for a string value is the first character of the string.) `%d, %i' These are equivalent; they both print a decimal integer. (The `%i' specification is for compatibility with ISO C.) `%e, %E' These print a number in scientific (exponential) notation; for example: d3908 3 a3910 4 prints `1.950e+03', with a total of four significant figures, three of which follow the decimal point. (The `4.3' represents two modifiers, discussed in the next node.) `%E' uses `E' instead of `e' in the output. d3912 2 a3913 2 `%f' This prints a number in floating-point notation. For example: d3917 14 a3930 12 prints `1950.000', with a total of four significant figures, three of which follow the decimal point. (The `4.3' represents two modifiers, discussed in the next node.) `%g, %G' These print a number in either scientific notation or in floating-point notation, whichever uses fewer characters; if the result is printed in scientific notation, `%G' uses `E' instead of `e'. `%o' This prints an unsigned octal integer. d3932 1 a3932 1 `%s' d3935 16 a3950 20 `%u' This prints an unsigned decimal integer. (This format is of marginal use, because all numbers in `awk' are floating-point; it is provided primarily for compatibility with C.) `%x, %X' These print an unsigned hexadecimal integer; `%X' uses the letters `A' through `F' instead of `a' through `f'. `%%' This isn't a format-control letter, but it does have meaning--the sequence `%%' outputs one `%'; it does not consume an argument and it ignores any modifiers. *Note:* When using the integer format-control letters for values that are outside the range of the widest C integer type, `gawk' switches to the the `%g' format specifier. If `--lint' is provided on the command line (*note Options::), `gawk' warns about this. Other versions of `awk' may print invalid values or do something else entirely. (d.c.) d3959 5 a3963 24 how much of the item's value is printed, as well as how much space it gets. The modifiers come between the `%' and the format-control letter. We will use the bullet symbol "*" in the following examples to represent spaces in the output. Here are the possible modifiers, in the order in which they may appear: `N$' An integer constant followed by a `$' is a "positional specifier". Normally, format specifications are applied to arguments in the order given in the format string. With a positional specifier, the format specification is applied to a specific argument, instead of what would be the next argument in the list. Positional specifiers begin counting with one. Thus: printf "%s %s\n", "don't", "panic" printf "%2$s %1$s\n", "panic", "don't" prints the famous friendly message twice. At first glance, this feature doesn't seem to be of much use. It is in fact a `gawk' extension, intended for use in translating messages at runtime. *Note Printf Ordering::, which describes how and why to use positional specifiers. For now, we will not use them. d3966 4 a3969 4 The minus sign, used before the width modifier (see later on in this table), says to left-justify the argument within its specified width. Normally, the argument is printed right-justified in the specified width. Thus: d3976 1 a3976 1 For numeric conversions, prefix positive values with a space and d3980 3 a3982 4 The plus sign, used before the width modifier (see later on in this table), says to always supply a sign for numeric conversions, even if the data to format is positive. The `+' overrides the space modifier. d3986 3 a3988 3 supply a leading zero. For `%x' and `%X', supply a leading `0x' or `0X' for a nonzero result. For `%e', `%E', and `%f', the result always contains a decimal point. For `%g' and `%G', d3992 4 a3995 4 A leading `0' (zero) acts as a flag that indicates that output should be padded with zeros instead of spaces. This applies even to non-numeric output formats. (d.c.) This flag only has an effect when the field width is wider than the value to print. d3999 4 a4002 3 Inserting any number between the `%' sign and the format-control character forces the field to expand to this width. The default way to do this is to pad with spaces on the left. For example: d4010 1 a4010 1 necessary. Thus, the following: d4020 8 a4027 18 A period followed by an integer constant specifies the precision to use when printing. The meaning of the precision varies by control letter: `%e', `%E', `%f' Number of digits to the right of the decimal point. `%g', `%G' Maximum number of significant digits. `%d', `%i', `%o', `%u', `%x', `%X' Minimum number of digits to print. `%s' Maximum number of characters from the string that should print. Thus, the following: d4035 2 a4036 2 and/or PREC values in the format string, they are passed in the argument list. For example: d4043 1 a4043 1 is exactly equivalent to: d4048 5 a4052 4 Both programs output `**abc'. Earlier versions of `awk' did not support this capability. If you must use such a version, you may simulate this feature by using concatenation to build up the format string, like so: d4059 1 a4059 1 This is not particularly easy to read but it does work. d4061 5 a4065 5 C programmers may be used to supplying additional `l', `L', and `h' modifiers in `printf' format strings. These are not valid in `awk'. Most `awk' implementations silently ignore these modifiers. If `--lint' is provided on the command line (*note Options::), `gawk' warns about their use. If `--posix' is supplied, their use is a fatal d4074 1 a4074 2 The following is a simple example of how to use `printf' to make an aligned table: d4078 4 a4081 4 This command prints the names of the bulletin boards (`$1') in the file `BBS-list' as a string of 10 characters that are left-justified. It also prints the phone numbers (`$2') next on the line. This produces an aligned two-column table of names and phone numbers, as shown here: d4096 13 a4108 13 In this case, the phone numbers had to be printed as strings because the numbers are separated by a dash. Printing the phone numbers as numbers would have produced just the first three digits: `555'. This would have been pretty confusing. It wasn't necessary to specify a width for the phone numbers because they are last on their lines. They don't need to have spaces after them. The table could be made to look even nicer by adding headings to the tops of the columns. This is done using the `BEGIN' pattern (*note BEGIN/END::) so that the headers are only printed once, at the beginning of the `awk' program: d4114 3 a4116 2 The above example mixed `print' and `printf' statements in the same program. Using just `printf' statements can produce the same results: d4122 3 a4124 3 Printing each column heading with the same format specification used for the column elements ensures that the headings are aligned just like the columns. d4134 3 a4136 4 At this point, it would be a worthwhile exercise to use the `printf' statement to line up the headings and table data for the `inventory-shipped' example that was covered earlier in the minor node on the `print' statement (*note Print::). d4144 3 a4146 3 So far, the output from `print' and `printf' has gone to the standard output, usually the terminal. Both `print' and `printf' can also send their output to other places. This is called "redirection". d4152 4 a4155 4 There are four forms of output redirection: output to a file, output appended to a file, output through a pipe to another command, and output to a coprocess. They are all shown for the `print' statement, but they work identically for `printf': d4159 3 a4161 3 named OUTPUT-FILE. The file name OUTPUT-FILE can be any expression. Its value is changed to a string and then used as a file name (*note Expressions::). d4166 6 a4171 5 (This is different from how you use redirections in shell scripts.) If OUTPUT-FILE does not exist, it is created. For example, here is how an `awk' program can write a list of BBS names to one file named `name-list', and a list of phone numbers to another file named `phone-list': a4183 2 Each output file contains one name or number per line. d4186 1 a4186 1 output file named OUTPUT-FILE. The difference between this and the d4194 1 a4194 1 pipe to COMMAND, and writes the values of ITEMS through this pipe d4198 5 a4202 4 Its value is converted to a string whose contents give the shell command to be run. For example, the following produces two files, one unsorted list of BBS names, and one list sorted in reverse alphabetical order: d4208 7 a4214 7 The unsorted list is written with an ordinary redirection, while the sorted list is written by piping through the `sort' utility. The next example uses redirection to mail a message to the mailing list `bug-system'. This might be useful when trouble is encountered in an `awk' script run periodically for system maintenance: d4223 2 a4224 50 variable `m'. It's then sent down the pipeline to the `mail' program. (The parentheses group the items to concatenate--see *Note Concatenation::.) The `close' function is called here because it's a good idea to close the pipe as soon as all the intended output has been sent to it. *Note Close Files And Pipes::, for more information. This example also illustrates the use of a variable to represent a FILE or COMMAND--it is not necessary to always use a string constant. Using a variable is generally a good idea, because `awk' requires that the string value be spelled identically every time. `print ITEMS |& COMMAND' This type of redirection prints the items to the input of COMMAND. The difference between this and the single-`|' redirection is that the output from COMMAND can be read with `getline'. Thus COMMAND is a "coprocess", which works together with, but subsidiary to, the `awk' program. This feature is a `gawk' extension, and is not available in POSIX `awk'. *Note Two-way I/O::, for a more complete discussion. Redirecting output using `>', `>>', `|', or `|&' asks the system to open a file, pipe, or coprocess only if the particular FILE or COMMAND you specify has not already been written to by your program or if it has been closed since it was last written to. It is a common error to use `>' redirection for the first `print' to a file, and then to use `>>' for subsequent output: # clear the file print "Don't panic" > "guide.txt" ... # append print "Avoid improbability generators" >> "guide.txt" This is indeed how redirections must be used from the shell. But in `awk', it isn't necessary. In this kind of case, a program should use `>' for all the `print' statements, since the output file is only opened once. Many `awk' implementations limit the number of pipelines that an `awk' program may have open to just one! In `gawk', there is no such limit. `gawk' allows a program to open as many pipelines as the underlying operating system permits. Advanced Notes: Piping into `sh' -------------------------------- d4226 18 a4243 14 A particularly powerful way to use redirection is to build command lines and pipe them into the shell, `sh'. For example, suppose you have a list of files brought over from a system where all the file names are stored in uppercase, and you wish to rename them to have names in all lowercase. The following program is both simple and efficient: { printf("mv %s %s\n", $0, tolower($0)) | "sh" } END { close("sh") } The `tolower' function returns its argument string with all uppercase characters converted to lowercase (*note String Functions::). The program builds up a list of command lines, using the `mv' utility to rename the files. It then sends the list to the shell for execution. a4250 17 `gawk' provides a number of special file names that it interprets internally. These file names provide access to standard file descriptors, process-related information, and TCP/IP networking. * Menu: * Special FD:: Special files for I/O. * Special Process:: Special files for process information. * Special Network:: Special files for network communications. * Special Caveats:: Things to watch out for.  File: gawk.info, Node: Special FD, Next: Special Process, Up: Special Files Special Files for Standard Descriptors -------------------------------------- d4255 4 a4258 4 often redirected with the shell, via the `<', `<<', `>', `>>', `>&', and `|' operators. Standard error is typically used for writing error messages; the reason there are two separate streams, standard output and standard error, is so that they can be redirected separately. d4265 4 a4268 4 This works by opening a pipeline to a shell command that can access the standard error stream that it inherits from the `awk' process. This is far from elegant, and it is also inefficient, because it requires a separate process. So people writing `awk' programs often don't do d4273 5 a4277 5 This usually has the same effect but not always: although the standard error stream is usually the terminal, it can be redirected; when that happens, writing to the terminal is not correct. In fact, if `awk' is run from a background job, it may not have a terminal at all. Then opening `/dev/tty' fails. d4280 3 a4282 5 streams, as well as any other inherited open files. If the file name matches one of these special names when `gawk' redirects input or output, then it directly uses the stream that the file name stands for. These special file names work for all operating systems that `gawk' has been ported to, not just those that are POSIX-compliant: d4294 5 a4298 4 The file associated with file descriptor N. Such a file must be opened by the program initiating the `awk' execution (typically the shell). Unless special pains are taken in the shell from which `gawk' is invoked, only descriptors 0, 1, and 2 are available. d4301 5 a4305 3 aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively. However, they are more self-explanatory. The proper way to write an error message in a `gawk' program is to use `/dev/stderr', like this: a4308 10 Note the use of quotes around the file name. Like any other redirection, the value must be a string. It is a common error to omit the quotes, which leads to confusing results.  File: gawk.info, Node: Special Process, Next: Special Network, Prev: Special FD, Up: Special Files Special Files for Process-Related Information --------------------------------------------- d4312 3 a4314 2 they must first be closed with the `close' function (*note Close Files And Pipes::). The file names are: d4318 1 a4318 1 in decimal form, terminated with a newline. d4322 1 a4322 1 process, in decimal form, terminated with a newline. d4326 1 a4326 1 process, in decimal form, terminated with a newline. d4350 2 a4351 2 returned by the `getgroups' system call. (Multiple groups may not be supported on all systems.) d4357 2 a4358 27 *Note:* The special files that provide process-related information are now considered obsolete and will disappear entirely in the next release of `gawk'. `gawk' prints a warning message every time you use one of these files. To obtain process-related information, use the `PROCINFO' array. *Note Auto-set::.  File: gawk.info, Node: Special Network, Next: Special Caveats, Prev: Special Process, Up: Special Files Special Files for Network Communications ---------------------------------------- Starting with version 3.1 of `gawk', `awk' programs can open a two-way TCP/IP connection, acting as either a client or a server. This is done using a special file name of the form: `/inet/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT' The PROTOCOL is one of `tcp', `udp', or `raw', and the other fields represent the other essential pieces of information for making a networking connection. These file names are used with the `|&' operator for communicating with a coprocess (*note Two-way I/O::). This is an advanced feature, mentioned here only for completeness. Full discussion is delayed until *Note TCP/IP Networking::.  File: gawk.info, Node: Special Caveats, Prev: Special Network, Up: Special Files d4360 12 a4371 31 Special File Name Caveats ------------------------- Here is a list of things to bear in mind when using the special file names that `gawk' provides: * Recognition of these special file names is disabled if `gawk' is in compatibility mode (*note Options::). * The special files that provide process-related information are now considered obsolete and will disappear entirely in the next release of `gawk'. `gawk' prints a warning message every time you use one of these files. To obtain process-related information, use the `PROCINFO' array. *Note Built-in Variables::. * Starting with version 3.1, `gawk' _always_ interprets these special file names.(1) For example, using `/dev/fd/4' for output actually writes on file descriptor 4, and not on a new file descriptor that is `dup''ed from file descriptor 4. Most of the time this does not matter; however, it is important to _not_ close any of the files related to file descriptors 0, 1, and 2. Doing so results in unpredictable behavior. ---------- Footnotes ---------- (1) Older versions of `gawk' would interpret these names internally only if the system did not actually have a `/dev/fd' directory or any of the other special files listed earlier. Usually this didn't make a difference, but sometimes it did; thus, it was decided to make `gawk''s behavior consistent on all systems and to have it always interpret the special file names itself. d4376 2 a4377 2 Closing Input and Output Redirections ===================================== d4380 6 a4385 5 `getline' more than once during the execution of an `awk' program (*note Getline::), the file is opened (or the command is executed) the first time only. At that time, the first record of input is read from that file or command. The next time the same file or command is used with `getline', another record is read from it, and so on. d4387 2 a4388 2 Similarly, when a file or pipe is opened for output, the file name or command associated with it is remembered by `awk', and subsequent d4392 4 a4395 4 This implies that special steps are necessary in order to read the same file again from the beginning, or to rerun a shell command (rather than reading more output from the same command). The `close' function makes these things possible: d4399 1 a4399 1 or: d4404 1 a4404 1 must _exactly_ match the string that was used to open the file or start d4416 6 a4421 5 command, reopens the file or reruns the command. Because the expression that you use to close a file or pipeline must exactly match the expression used to open the file or run the command, it is good practice to use a variable to store the file name or command. The previous example becomes the following: d4429 3 a4431 1 programs. Here are some of the reasons for closing an output file: d4434 2 a4435 2 program. Close the file after writing it, then begin reading it with `getline'. d4438 10 a4447 10 If the files aren't closed, eventually `awk' may exceed a system limit on the number of open files in one process. It is best to close each one when the program has finished writing it. * To make a command finish. When output is redirected through a pipe, the command reading the pipe normally continues to try to read input as long as the pipe is open. Often this means the command cannot really do its work until the pipe is closed. For example, if output is redirected to the `mail' program, the message is not actually sent until the pipe is closed. d4452 9 a4460 5 For example, suppose a program pipes output to the `mail' program. If it outputs several lines redirected to this pipe without closing it, they make a single message of several lines. By contrast, if the program closes the pipe after each line of output, then each line makes a separate message. d4463 5 a4467 82 `gawk' attempts to multiplex the available open files among your data files. `gawk''s ability to do this depends upon the facilities of your operating system, so it may not always work. It is therefore both good practice and good portability advice to always use `close' on your files when you are done with them. In fact, if you are using a lot of pipes, it is essential that you close commands when done. For example, consider something like this: { ... command = ("grep " $1 " /some/file | my_prog -q " $3) while ((command | getline) > 0) { PROCESS OUTPUT OF command } # need close(command) here } This example creates a new pipeline based on data in _each_ record. Without the call to `close' indicated in the comment, `awk' creates child processes to run the commands, until it eventually runs out of file descriptors for more pipelines. Even though each command has finished (as indicated by the end-of-file return status from `getline'), the child process is not terminated;(1) more importantly, the file descriptor for the pipe is not closed and released until `close' is called or `awk' exits. `close' will silently do nothing if given an argument that does not represent a file, pipe or coprocess that was opened with a redirection. Note also that `close(FILENAME)' has no "magic" effects on the implicit loop that reads through the files named on the command line. It is, more likely, a close of a file that was never opened, so `awk' silently does nothing. When using the `|&' operator to communicate with a coprocess, it is occasionally useful to be able to close one end of the two-way pipe without closing the other. This is done by supplying a second argument to `close'. As in any other call to `close', the first argument is the name of the command or special file used to start the coprocess. The second argument should be a string, with either of the values `"to"' or `"from"'. Case does not matter. As this is an advanced feature, a more complete discussion is delayed until *Note Two-way I/O::, which discusses it in more detail and gives an example. Advanced Notes: Using `close''s Return Value -------------------------------------------- In many versions of Unix `awk', the `close' function is actually a statement. It is a syntax error to try and use the return value from `close': (d.c.) command = "..." command | getline info retval = close(command) # syntax error in most Unix awks `gawk' treats `close' as a function. The return value is -1 if the argument names something that was never opened with a redirection, or if there is a system problem closing the file or process. In these cases, `gawk' sets the built-in variable `ERRNO' to a string describing the problem. In `gawk', when closing a pipe or coprocess, the return value is the exit status of the command.(2) Otherwise, it is the return value from the system's `close' or `fclose' C functions when closing input or output files, respectively. This value is zero if the close succeeds, or -1 if it fails. The POSIX standard is very vague; it says that `close' returns zero on success and non-zero otherwise. In general, different implementations vary in what they report when closing pipes; thus the return value cannot be used portably. (d.c.) ---------- Footnotes ---------- (1) The technical terminology is rather morbid. The finished child is called a "zombie," and cleaning up after it is referred to as "reaping." (2) This is a full 16-bit value as returned by the `wait' system call. See the system manual pages for information on how to decode this value. d4476 4 a4479 3 actions. An expression evaluates to a value that you can print, test, or pass to a function. Additionally, an expression can assign a new value to a variable or a field by using an assignment operator. d4482 4 a4485 5 Most other kinds of statements contain one or more expressions that specify the data on which to operate. As in other languages, expressions in `awk' include variables, array references, constants, and function calls, as well as combinations of these with various operators. d4489 1 a4489 1 * Constants:: String, numeric and regexp constants. d4499 2 a4500 2 * Truth Values:: What is ``true'' and what is ``false''. * Typing and Comparison:: How variables acquire types and how this d4504 2 a4505 2 operators `||' (``or''), `&&' (``and'') and `!' (``not''). d4513 1 a4513 1 File: gawk.info, Node: Constants, Next: Using Constant Regexps, Up: Expressions d4519 2 a4520 6 the same value. There are three types of constants: numeric, string, and regular expression. Each is used in the appropriate context when you need a data value that isn't going to change. Numeric constants can have different forms, but are stored identically internally. a4524 1 * Nondecimal-numbers:: What are octal and hex numbers. d4528 1 a4528 1 File: gawk.info, Node: Scalar Constants, Next: Nondecimal-numbers, Up: Constants d4535 2 a4536 2 notation.(1) Here are some examples of numeric constants that all have the same value: d4543 1 a4543 1 double-quotation marks. For example: d4548 3 a4550 4 can be of any length, and they can contain any of the possible eight-bit ASCII characters including ASCII NUL (character code zero). Other `awk' implementations may have difficulty with some character codes. d4554 3 a4556 78 (1) The internal representation of all numbers, including integers, uses double-precision floating-point numbers. On most modern systems, these are in IEEE 754 standard format.  File: gawk.info, Node: Nondecimal-numbers, Next: Regexp Constants, Prev: Scalar Constants, Up: Constants Octal and Hexadecimal Numbers ----------------------------- In `awk', all numbers are in decimal; i.e., base 10. Many other programming languages allow you to specify numbers in other bases, often octal (base 8) and hexadecimal (base 16). In octal, the numbers go 0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, etc. Just as `11', in decimal, is 1 times 10 plus 1, so `11', in octal, is 1 times 8, plus 1. This equals 9 in decimal. In hexadecimal, there are 16 digits. Since the everyday decimal number system only has ten digits (`0'-`9'), the letters `a' through `f' are used to represent the rest. (Case in the letters is usually irrelevant; hexadecimal `a' and `A' have the same value.) Thus, `11', in hexadecimal, is 1 times 16 plus 1, which equals 17 in decimal. Just by looking at plain `11', you can't tell what base it's in. So, in C, C++, and other languages derived from C, there is a special notation to help signify the base. Octal numbers start with a leading `0', and hexadecimal numbers start with a leading `0x' or `0X': `11' Decimal value 11. `011' Octal 11, decimal value 9. `0x11' Hexadecimal 11, decimal value 17. This example shows the difference: $ gawk 'BEGIN { printf "%d, %d, %d\n", 011, 11, 0x11 }' -| 9, 11, 17 Being able to use octal and hexadecimal constants in your programs is most useful when working with data that cannot be represented conveniently as characters or as regular numbers, such as binary data of various sorts. `gawk' allows the use of octal and hexadecimal constants in your program text. However, such numbers in the input data are not treated differently; doing so by default would break old programs. (If you really need to do this, use the `--non-decimal-data' command-line option; *note Nondecimal Data::.) If you have octal or hexadecimal data, you can use the `strtonum' function (*note String Functions::) to convert the data into a number. Most of the time, you will want to use octal or hexadecimal constants when working with the built-in bit manipulation functions; see *Note Bitwise Functions::, for more information. Unlike some early C implementations, `8' and `9' are not valid in octal constants; e.g., `gawk' treats `018' as decimal 18: $ gawk 'BEGIN { print "021 is", 021 ; print 018 }' -| 021 is 17 -| 18 Octal and hexadecimal source code constants are a `gawk' extension. If `gawk' is in compatibility mode (*note Options::), they are not available. Advanced Notes: A Constant's Base Does Not Affect Its Value ----------------------------------------------------------- Once a numeric constant has been converted internally into a number, `gawk' no longer remembers what the original form of the constant was; the internal value is always used. This has particular consequences for conversion of numbers to strings: $ gawk 'BEGIN { printf "0x11 is <%s>\n", 0x11 }' -| 0x11 is <17> d4559 1 a4559 1 File: gawk.info, Node: Regexp Constants, Prev: Nondecimal-numbers, Up: Constants d4576 1 a4576 1 When used on the righthand side of the `~' or `!~' operators, a d4578 2 a4579 1 However, regexp constants (such as `/foo/') may be used like simple d4581 3 a4583 3 meaning as if it appeared in a pattern, i.e., `($0 ~ /foo/)' (d.c.) *Note Expression Patterns::. This means that the following two code segments: d4588 1 a4588 1 and: d4593 5 a4597 3 are exactly equivalent. One rather bizarre consequence of this rule is that the following Boolean expression is valid, but does not do what the user probably intended: d4605 9 a4613 6 the regexp `/foo/'. The result is either zero or one, depending upon the success or failure of the match. That result is then matched against the first field in the record. Because it is unlikely that you would ever really want to make this kind of test, `gawk' issues a warning when it sees this construct in a program. Another consequence of this rule is that the assignment statement: d4617 5 a4621 3 assigns either zero or one to the variable `matches', depending upon the contents of the current input record. This feature of the language has never been well documented until the POSIX specification. d4624 9 a4632 7 the `gensub', `sub', and `gsub' functions, and as the second argument of the `match' function (*note String Functions::). Modern implementations of `awk', including `gawk', allow the third argument of `split' to be a regexp constant, but some older implementations do not. (d.c.) This can lead to confusion when attempting to use regexp constants as arguments to user-defined functions (*note User-defined::). For example: d4650 9 a4658 7 In this example, the programmer wants to pass a regexp constant to the user-defined function `mysub', which in turn passes it on to either `sub' or `gsub'. However, what really happens is that the `pat' parameter is either one or zero, depending upon whether or not `$0' matches `/hi/'. `gawk' issues a warning when it sees a regexp constant used as a parameter to a user-defined function, since passing a truth value in this way is probably not what was intended. d4667 3 a4669 3 use later in another part of your program. They can be manipulated entirely within the program text, and they can also be assigned values on the `awk' command line. d4674 2 a4675 2 * Assignment Options:: Setting variables on the command-line and a summary of command-line syntax. This is an d4679 1 a4679 1 File: gawk.info, Node: Using Variables, Next: Assignment Options, Up: Variables d4684 5 a4688 5 Variables let you give names to values and refer to them later. Variables have already been used in many of the examples. The name of a variable must be a sequence of letters, digits, or underscores, and it may not begin with a digit. Case is significant in variable names; `a' and `A' are distinct variables. d4692 2 a4693 2 "assignment operators", "increment operators", and "decrement operators". *Note Assignment Ops::. d4695 6 a4700 7 A few variables have special built-in meanings, such as `FS' (the field separator), and `NF' (the number of fields in the current input record). *Note Built-in Variables::, for a list of the built-in variables. These built-in variables can be used and assigned just like all other variables, but their values are also used or changed automatically by `awk'. All built-in variables' names are entirely uppercase. d4703 4 a4706 5 The kind of value a variable holds can change over the life of a program. By default, variables are initialized to the empty string, which is zero if converted to a number. There is no need to "initialize" each variable explicitly in `awk', which is what you would do in C and in most other traditional languages. d4714 4 a4717 3 Any `awk' variable can be set by including a "variable assignment" among the arguments on the command line when `awk' is invoked (*note Other Arguments::). Such an assignment has the following form: d4721 4 a4724 3 With it, a variable is set either at the beginning of the `awk' run or in between input files. When the assignment is preceded with the `-v' option, as in the following: d4728 1 a4728 1 the variable is set at the very beginning, even before the `BEGIN' d4730 6 a4735 5 file name arguments, as well as the program text. (*Note Options::, for more information about the `-v' option.) Otherwise, the variable assignment is performed at a time determined by its position among the input file arguments--after the processing of the preceding input file argument. For example: d4744 1 a4744 1 second field is printed in lines from `BBS-list': d4754 6 a4759 4 Command-line arguments are made available for explicit examination by the `awk' program in the `ARGV' array (*note ARGC and ARGV::). `awk' processes the values of command-line assignments for escape sequences (*note Escape Sequences::). (d.c.) d4767 6 a4772 6 Strings are converted to numbers and numbers are converted to strings, if the context of the `awk' program demands it. For example, if the value of either `foo' or `bar' in the expression `foo + bar' happens to be a string, it is converted to a number before the addition is performed. If numeric values appear in string concatenation, they are converted to strings. Consider the following: d4779 2 a4780 2 together. The resulting string is converted back to the number 23, to which 4 is then added. d4784 4 a4787 3 a string to be converted to a number, add zero to that string. A string is converted to a number by interpreting any numeric prefix of the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to d4789 1 a4789 1 interpreted as valid numbers convert to zero. d4793 3 a4795 2 Variables::). Numbers are converted using the `sprintf' function with `CONVFMT' as the format specifier (*note String Functions::). d4798 12 a4809 12 least six significant digits. For some applications, you might want to change it to specify more precision. On most modern machines, 17 digits is enough to capture a floating-point number's value exactly, most of the time.(1) Strange results can occur if you set `CONVFMT' to a string that doesn't tell `sprintf' how to format floating-point numbers in a useful way. For example, if you forget the `%' in the format, `awk' converts all numbers to the same constant string. As a special case, if a number is an integer, then the result of converting it to a string is _always_ an integer, no matter what the value of `CONVFMT' may be. Given the following code fragment: d4815 1 a4815 1 `b' has the value `"12"', not `"12.00"'. (d.c.) d4817 11 a4827 49 Prior to the POSIX standard, `awk' used the value of `OFMT' for converting numbers to strings. `OFMT' specifies the output format to use when printing numbers with `print'. `CONVFMT' was introduced in order to separate the semantics of conversion from the semantics of printing. Both `CONVFMT' and `OFMT' have the same default value: `"%.6g"'. In the vast majority of cases, old `awk' programs do not change their behavior. However, these semantics for `OFMT' are something to keep in mind if you must port your new style program to older implementations of `awk'. We recommend that instead of changing your programs, just port `gawk' itself. *Note Print::, for more information on the `print' statement. Finally, once again, where you are can matter when it comes to converting between numbers and strings. In *Note Locales::, we mentioned that the local character set and language (the locale) can affect how `gawk' matches characters. The locale also affects numeric formats. In particular, for `awk' programs, it affects the decimal point character. The `"C"' locale, and most English-language locales, use the period character (`.') as the decimal point. However, many (if not most) European and non-English locales use the comma (`,') as the decimal point character. The POSIX standard says that `awk' always uses the period as the decimal point when reading the `awk' program source code, and for command-line variable assignments (*note Other Arguments::). However, when interpreting input data, for `print' and `printf' output, and for number to string conversion, the local decimal point character is used. As of version 3.1.3, `gawk' fully complies with this aspect of the standard. Here are some examples indicating the difference in behavior, on a GNU/Linux system: $ gawk 'BEGIN { printf "%g\n", 3.1415927 }' -| 3.14159 $ LC_ALL=en_DK gawk 'BEGIN { printf "%g\n", 3.1415927 }' -| 3,14159 $ echo 4,321 | gawk '{ print $1 + 1 }' -| 5 $ echo 4,321 | LC_ALL=en_DK gawk '{ print $1 + 1 }' -| 5,321 The `en_DK' locale is for English in Denmark, where the comma acts as the decimal point separator. In the normal `"C"' locale, `gawk' treats `4,321' as `4', while in the Danish locale, it's treated as the full number, `4.321'. ---------- Footnotes ---------- (1) Pathological cases can require up to 752 digits (!), but we doubt that you need to worry about this. d4837 1 a4837 1 precedence rules and work as you would expect them to. d4839 2 a4840 3 The following example uses a file named `grades', which contains a list of student names as well as three test scores per student (it's a small class): d4846 2 a4847 2 This programs takes the file `grades' and prints the average of the scores: d4855 2 a4856 2 The following list provides the arithmetic operators in `awk', in order from the highest precedence to the lowest: d4862 1 a4862 1 Unary plus; the expression is converted to a number. d4866 3 a4868 2 Exponentiation; X raised to the Y power. `2 ^ 3' has the value eight; the character sequence `**' is equivalent to `^'. d4874 2 a4875 6 Division; because all numbers in `awk' are floating-point numbers, the result is _not_ rounded to an integer--`3 / 4' has the value 0.75. (It is a common mistake, especially for C programmers, to forget that _all_ numbers in `awk' are floating-point, and that division of integer-looking constants produces a real number, not an integer.) d4878 14 a4891 2 Remainder; further discussion is provided in the text, just after this list. d4899 2 a4904 18 When computing the remainder of `X % Y', the quotient is rounded toward zero to an integer and multiplied by Y. This result is subtracted from X; this operation is sometimes known as "trunc-mod." The following relation always holds: b * int(a / b) + (a % b) == a One possibly undesirable effect of this definition of remainder is that `X % Y' is negative if X is negative. Thus: -17 % 8 = -1 In other `awk' implementations, the signedness of the remainder may be machine-dependent. *Note:* The POSIX standard only specifies the use of `^' for exponentiation. For maximum portability, do not use the `**' operator. d4925 1 a4925 1 runs together. For example: d4932 3 a4934 3 Because string concatenation does not have an explicit operator, it is often necessary to insure that it happens at the right time by using parentheses to enclose the items to concatenate. For example, the d4946 2 a4947 39 Parentheses should be used around concatenation in all but the most common contexts, such as on the righthand side of `='. Be careful about the kinds of expressions used in string concatenation. In particular, the order of evaluation of expressions used for concatenation is undefined in the `awk' language. Consider this example: BEGIN { a = "don't" print (a " " (a = "panic")) } It is not defined whether the assignment to `a' happens before or after the value of `a' is retrieved for producing the concatenated value. The result could be either `don't panic', or `panic panic'. The precedence of concatenation, when mixed with other operators, is often counter-intuitive. Consider this example: $ awk 'BEGIN { print -12 " " -24 }' -| -12-24 This "obviously" is concatenating -12, a space, and -24. But where did the space disappear to? The answer lies in the combination of operator precedences and `awk''s automatic conversion rules. To get the desired result, write the program in the following manner: $ awk 'BEGIN { print -12 " " (-24) }' -| -12 -24 This forces `awk' to treat the `-' on the `-24' as unary. Otherwise, it's parsed as follows: -12 (`" "' - 24) => -12 (0 - 24) => -12 (-24) => -12-24 As mentioned earlier, when doing concatenation, _parenthesize_. Otherwise, you're never quite sure what you'll get. d4955 2 a4956 3 An "assignment" is an expression that stores a (usually different) value into a variable. For example, let's assign the value one to the variable `z': d4963 2 a4964 3 Assignments can also store string values. For example, the following stores the value `"this food is good"' in the variable `message': d4970 25 a4994 20 This also illustrates string concatenation. The `=' sign is called an "assignment operator". It is the simplest assignment operator because the value of the righthand operand is stored unchanged. Most operators (addition, concatenation, and so on) have no effect except to compute a value. If the value isn't used, there's no reason to use the operator. An assignment operator is different; it does produce a value, but even if you ignore it, the assignment still makes itself felt through the alteration of the variable. We call this a "side effect". The lefthand operand of an assignment need not be a variable (*note Variables::); it can also be a field (*note Changing Fields::) or an array element (*note Arrays::). These are all called "lvalues", which means they can appear on the lefthand side of an assignment operator. The righthand operand may be any expression; it produces the new value that the assignment stores in the specified variable, field, or array element. (Such values are called "rvalues".) It is important to note that variables do _not_ have permanent types. A variable's type is simply the type of whatever value it happens to hold at the moment. In the following program fragment, the variable d5006 1 a5006 1 zero. After executing the following code, the value of `foo' is five: d5011 4 a5014 3 *Note:* Using a variable as a number and then later as a string can be confusing and is poor programming style. The previous two examples illustrate how `awk' works, _not_ how you should write your programs! d5016 2 a5017 2 An assignment is an expression, so it has a value--the same value that is assigned. Thus, `z = 1' is an expression with the value one. d5019 1 a5019 1 together, such as: d5021 1 a5021 1 x = y = z = 5 d5023 9 a5031 10 This example stores the value five in all three variables (`x', `y', and `z'). It does so because the value of `z = 5', which is five, is stored into `y' and then the value of `y = z = 5', which is five, is stored into `x'. Assignments may be used anywhere an expression is called for. For example, it is valid to write `x != (y = 1)' to set `y' to one, and then test whether `x' equals one. But this style tends to make programs hard to read; such nesting of assignments should be avoided, except perhaps in a one-shot program. d5035 3 a5037 3 operator `+=' computes a new value by adding the righthand value to the old value of the variable. Thus, the following assignment adds five to the value of `foo': d5045 1 a5045 1 Use whichever makes the meaning of your program clearer. d5048 2 a5049 2 is _not_ the same as simply repeating the lefthand operand in the righthand expression. For example: d5062 11 a5072 8 The indices of `bar' are practically guaranteed to be different, because `rand' returns different values each time it is called. (Arrays and the `rand' function haven't been covered yet. *Note Arrays::, and see *Note Numeric Functions::, for more information). This example illustrates an important fact about assignment operators: the lefthand expression is only evaluated _once_. It is up to the implementation as to which expression is evaluated first, the lefthand or the righthand. Consider this example: d5080 1 a5080 1 case, the righthand operand is an expression whose value is converted d5083 6 a5088 24 LVALUE `+=' INCREMENT Adds INCREMENT to the value of LVALUE. LVALUE `-=' DECREMENT Subtracts DECREMENT from the value of LVALUE. LVALUE `*=' Multiplies the value of LVALUE by COEFFICIENT. COEFFICIENT LVALUE `/=' DIVISOR Divides the value of LVALUE by DIVISOR. LVALUE `%=' MODULUS Sets LVALUE to its remainder by MODULUS. LVALUE `^=' POWER LVALUE `**=' POWER Raises LVALUE to the power POWER. *Note:* Only the `^=' operator is specified by POSIX. For maximum portability, do not use the `**=' operator. Advanced Notes: Syntactic Ambiguities Between `/=' and Regular Expressions -------------------------------------------------------------------------- There is a syntactic ambiguity between the `/=' assignment operator and regexp constants whose first character is an `='. (d.c.) This is most notable in commercial `awk' versions. For example: $ awk /==/ /dev/null error--> awk: syntax error at source line 1 error--> context is error--> >>> /= <<< error--> awk: bailing out at source line 1 d5090 2 a5091 1 A workaround is: d5093 2 a5094 1 awk '/[=]=/' /dev/null d5096 9 a5104 2 `gawk' does not have this problem, nor do the other freely available versions described in *Note Other Versions::. d5113 35 a5147 32 of a variable by one. An assignment operator can do the same thing, so the increment operators add no power to the `awk' language; however, they are convenient abbreviations for very common operations. The operator used for adding one is written `++'. It can be used to increment a variable either before or after taking its value. To pre-increment a variable `v', write `++v'. This adds one to the value of `v'--that new value is also the value of the expression. (The assignment expression `v += 1' is completely equivalent.) Writing the `++' after the variable specifies post-increment. This increments the variable value just the same; the difference is that the value of the increment expression itself is the variable's _old_ value. Thus, if `foo' has the value four, then the expression `foo++' has the value four, but it changes the value of `foo' to five. In other words, the operator returns the old value of the variable, but with the side effect of incrementing it. The post-increment `foo++' is nearly the same as writing `(foo += 1) - 1'. It is not perfectly equivalent because all numbers in `awk' are floating-point--in floating-point, `foo + 1 - 1' does not necessarily equal `foo'. But the difference is minute as long as you stick to numbers that are fairly small (less than 10e12). Fields and array elements are incremented just like variables. (Use `$(i++)' when you want to do a field reference and a variable increment at the same time. The parentheses are necessary because of the precedence of the field reference operator `$'.) The decrement operator `--' works just like `++', except that it subtracts one instead of adding it. As with `++', it can be used before the lvalue to pre-decrement or after it to post-decrement. Following is a summary of increment and decrement expressions: d5150 1 a5150 1 This expression increments LVALUE, and the new value becomes the d5155 1 a5155 1 is the _old_ value of LVALUE. d5158 2 a5159 3 This expression is like `++LVALUE', but instead of adding, it subtracts. It decrements LVALUE and delivers the value that is the result. d5162 3 a5164 31 This expression is like `LVALUE++', but instead of adding, it subtracts. It decrements LVALUE. The value of the expression is the _old_ value of LVALUE. Advanced Notes: Operator Evaluation Order ----------------------------------------- Doctor, doctor! It hurts when I do this! So don't do that! Groucho Marx What happens for something like the following? b = 6 print b += b++ Or something even stranger? b = 6 b += ++b + b++ print b In other words, when do the various side effects prescribed by the postfix operators (`b++') take effect? When side effects happen is "implementation defined". In other words, it is up to the particular version of `awk'. The result for the first example may be 12 or 13, and for the second, it may be 22 or 23. In short, doing things like this is not recommended and definitely not anything that you can rely upon for portability. You should avoid such things in your own programs. d5174 7 a5180 6 constants `true' and `false', or perhaps their uppercase equivalents. However, `awk' is different. It borrows a very simple concept of true and false from C. In `awk', any nonzero numeric value _or_ any nonempty string value is true. Any other value (zero or the null string `""') is false. The following program prints `A strange truth value' three times: d5191 2 a5192 3 There is a surprising consequence of the "nonzero or non-null" rule: the string constant `"0"' is actually true, because it is non-null. (d.c.) d5208 1 a5208 1 string", which is simply a string that looks like a number--for d5210 4 a5213 3 variable. The type of the variable is important because the types of two variables determine how they are compared. In `gawk', variable typing follows these rules: d5215 3 a5217 1 * A numeric constant or the result of a numeric operation has the d5220 2 a5221 2 * A string constant or the result of a string operation has the STRING attribute. d5223 2 a5224 2 * Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON' elements, and the elements of an array created by `split' that are d5229 2 a5230 2 * Attributes propagate across assignments but are not changed by any use. d5234 1 a5234 1 operation: d5243 2 a5244 2 comparison may be used. This depends upon the attributes of the operands, according to the following symmetric matrix: d5246 2 a5247 2 +---------------------------------------------- | STRING NUMERIC STRNUM d5249 6 a5254 6 | STRING | string string string | NUMERIC | string numeric numeric | STRNUM | string numeric numeric d5257 3 a5259 9 The basic idea is that user input that looks numeric--and _only_ user input--should be treated as numeric, even though it is actually made of characters and is therefore also a string. Thus, for example, the string constant `" +3.14"' is a string, even though it looks numeric, and is _never_ treated as number for comparison purposes. In short, when one operand is a "pure" string, such as a string constant, then a string comparison is performed. Otherwise, a numeric comparison is performed.(1) d5295 4 a5298 2 When comparing operands of mixed types, numeric operands are converted to strings using the value of `CONVFMT' (*note Conversion::). d5301 1 a5301 1 the second character of each, and so on. Thus, `"10"' is less than d5303 1 a5303 1 the shorter string is less than the longer one. Thus, `"abc"' is less d5306 3 a5308 3 It is very easy to accidentally mistype the `==' operator and leave off one of the `=' characters. The result is still valid `awk' code, but the program does not do what is intended: d5316 2 a5317 2 test always succeeds. Because the operators are so similar, this kind of error is very difficult to spot when scanning the source code. d5319 2 a5320 2 The following table of expressions illustrates the kind of comparison `gawk' performs, as well as what the result of the comparison is: a5338 1 d5342 1 a5342 1 In the next example: d5347 9 a5355 7 the result is `false' because both `$1' and `$2' are user input. They are numeric strings--therefore both have the STRNUM attribute, dictating a numeric comparison. The purpose of the comparison rules and the use of numeric strings is to attempt to produce the behavior that is "least surprising," while still "doing the right thing." String comparisons and regular expression comparisons are very different. For example: d5359 2 a5360 2 has the value one, or is true if the variable `x' is precisely `foo'. By contrast: d5367 5 a5371 4 The righthand operand of the `~' and `!~' operators may be either a regexp constant (`/.../') or an ordinary expression. In the latter case, the value of the expression as a string is used as a dynamic regexp (*note Regexp Usage::; also *note Computed Regexps::). d5373 1 a5373 1 In modern implementations of `awk', a constant regular expression in d5375 1 a5375 1 abbreviation for the following comparison expression: d5379 4 a5382 9 One special place where `/foo/' is _not_ an abbreviation for `$0 ~ /foo/' is when it is the righthand operand of `~' or `!~'. *Note Using Constant Regexps::, where this is discussed in more detail. ---------- Footnotes ---------- (1) The POSIX standard is under revision. The revised standard's rules for typing and comparison are the same as just described for `gawk'. d5390 2 a5391 2 A "Boolean expression" is a combination of comparison expressions or matching expressions, using the Boolean operators "or" (`||'), "and" d5393 1 a5393 1 The truth value of the Boolean expression is computed by combining the d5398 10 a5407 8 expressions can be used. They can be used in `if', `while', `do', and `for' statements (*note Statements::). They have numeric values (one if true, zero if false) that come into play if the result of the Boolean expression is stored in a variable or used in arithmetic. In addition, every Boolean expression is also a valid pattern, so you can use one as a pattern to control the execution of rules. The Boolean operators are: d5412 1 a5412 1 both `2400' and `foo': d5418 3 a5420 3 have side effects. In the case of `$0 ~ /foo/ && ($2 == bar++)', the variable `bar' is not incremented if there is no substring `foo' in the record. d5425 1 a5425 1 that contain _either_ `2400' or `foo' or both: d5435 2 a5436 5 prints `no home!' in the unusual event that the `HOME' environment variable is not defined: BEGIN { if (! ("HOME" in ENVIRON)) print "no home!" } d5438 1 a5438 1 (The `in' operator is described in *Note Reference to Elements::.) d5445 12 a5456 11 Statements that use `&&' or `||' can be continued simply by putting a newline after them. But you cannot put a newline in front of either of these operators without using backslash continuation (*note Statements/Lines::). The actual value of an expression using the `!' operator is either one or zero, depending upon the truth value of the expression it is applied to. The `!' operator is often useful for changing the sense of a flag variable from false to true and back again. For example, the following program is one way to print lines in between special bracketing lines: d5458 1 a5458 1 $1 == "START" { interested = ! interested; next } d5460 1 a5460 1 $1 == "END" { interested = ! interested; next } d5462 1 a5462 1 The variable `interested', as with all `awk' variables, starts out a5468 5 *Note:* The `next' statement is discussed in *Note Next Statement::. `next' tells `awk' to skip the rest of the rules, get the next record, and start processing the rules over again at the top. The reason it's there is to avoid printing the bracketing `START' and `END' lines. d5475 1 a5475 1 A "conditional expression" is a special kind of expression that has d5477 3 a5479 2 one of two other expressions. The conditional expression is the same as in the C language, as shown here: d5484 1 a5484 1 computed first. If it is "true" (not zero or not null), then d5487 1 a5487 2 value becomes the value of the whole expression. For example, the following expression produces the absolute value of `x': d5489 1 a5489 1 x >= 0 ? x : -x d5491 7 a5497 5 Each time the conditional expression is computed, only one of IF-TRUE-EXP and IF-FALSE-EXP is used; the other is ignored. This is important when the expressions have side effects. For example, this conditional expression examines element `i' of either array `a' or array `b', and increments `i': d5502 2 a5503 2 only one of the two increment expressions is executed and the other is not. *Note Arrays::, for more information about arrays. d5505 5 a5509 5 As a minor `gawk' extension, a statement that uses `?:' can be continued simply by putting a newline after either character. However, putting a newline in front of either character does not work without using backslash continuation (*note Statements/Lines::). If `--posix' is specified (*note Options::), then this extension is disabled. d5517 3 a5519 3 A "function" is a name for a particular calculation. This enables you to ask for it by name at any point in the program. For example, the function `sqrt' computes the square root of a number. d5523 4 a5526 3 *Note Built-in::, for a list of built-in functions and their descriptions. In addition, you can define functions for use in your program. *Note User-defined::, for instructions on how to do this. d5530 5 a5534 5 "arguments" in parentheses. The arguments are expressions that provide the raw materials for the function's calculations. When there is more than one argument, they are separated by commas. If there are no arguments, just write `()' after the function name. The following examples show function calls with and without arguments: d5540 3 a5542 3 *Caution:* Do not put any space between the function name and the open-parenthesis! A user-defined function name looks just like the name of a variable--a space would make the expression look like d5544 7 a5550 7 With built-in functions, space before the parenthesis is harmless, but it is best not to get into the habit of using space to avoid mistakes with user-defined functions. Each function expects a particular number of arguments. For example, the `sqrt' function must be called with a single argument, the number of which to take the square root: d5554 6 a5559 6 Some of the built-in functions have one or more optional arguments. If those arguments are not supplied, the functions use a reasonable default value. *Note Built-in::, for full details. If arguments are omitted in calls to user-defined functions, then those arguments are treated as local variables and initialized to the empty string (*note User-defined::). d5565 4 a5568 2 certain variables or doing I/O. The following program reads numbers, one number per line, and prints the square root of each one: d5577 1 a5577 1 Ctrl-d d5585 1 a5585 1 "Operator precedence" determines how operators are grouped when d5588 1 a5588 1 `b' and `c', and then add `a' to the product (i.e., `a + (b * c)'). d5590 8 a5597 8 The normal precedence of the operators can be overruled by using parentheses. Think of the precedence rules as saying where the parentheses are assumed to be. In fact, it is wise to always use parentheses whenever there is an unusual combination of operators, because other people who read the program may not remember what the precedence is in this case. Even experienced programmers occasionally forget the exact rules, which leads to mistakes. Explicit parentheses help prevent any such mistakes. d5600 1 a5600 1 operator groups first, except for the assignment, conditional, and d5602 1 a5602 1 - b + c' groups as `(a - b) + c' and `a = b = c' groups as `a = (b = d5607 1 a5607 1 interpret them: innermost first. Thus, `$++i' means `$(++i)' and d5609 6 a5614 4 operand, then the precedence of the unary operators can matter. `$x^2' means `($x)^2', but `-x^2' means `-(x^2)', because `-' has lower precedence than `^', whereas `$' has higher precedence. This table presents `awk''s operators, in order of highest to lowest precedence: d5626 2 a5627 1 Exponentiation. These operators group right-to-left. d5630 1 a5630 1 Unary plus, minus, logical "not." d5638 3 a5640 3 `String Concatenation' No special symbol is used to indicate concatenation. The operands are simply written side by side (*note Concatenation::). d5643 2 a5644 2 `> >= >> | |&' Relational and redirection. The relational operators and the d5651 1 a5651 1 redirection does not produce an expression that could be the d5654 3 a5656 3 precedence without parentheses. Such combinations (for example, `print foo > a ? b : c'), result in syntax errors. The correct way to write this statement is `print foo > (a ? b : c)'. d5659 1 a5659 1 Matching, nonmatching. d5675 2 a5676 4 Assignment. These operators group right to left. *Note:* The `|&', `**', and `**=' operators are not specified by POSIX. For maximum portability, do not use them. d5679 1 a5679 1 File: gawk.info, Node: Patterns and Actions, Next: Arrays, Prev: Expressions, Up: Top d5681 2 a5682 2 Patterns, Actions, and Variables ******************************** d5685 2 a5686 8 with an associated action. This major node describes how you build patterns and actions, what kinds of things you can do within actions, and `awk''s built-in variables. The pattern-action rules and the statements available for use within actions form the core of `awk' programming. In a sense, everything covered up to here has been the foundation that programs are built on top of. Now it's time to start building something useful. a5690 1 * Using Shell Variables:: How to use shell variables with `awk'. a5691 3 * Statements:: Describes the various control statements in detail. * Built-in Variables:: Summarizes the built-in variables. d5694 1 a5694 1 File: gawk.info, Node: Pattern Overview, Next: Using Shell Variables, Up: Patterns and Actions d5699 4 d5705 1 d5712 7 a5718 3 Patterns in `awk' control the execution of rules--a rule is executed when its pattern matches the current input record. The following is a summary of the types of `awk' patterns: d5721 3 a5723 2 A regular expression. It matches when the text of the input record fits the regular expression. (*Note Regexp::.) d5726 3 a5728 2 A single expression. It matches when its value is nonzero (if a number) or non-null (if a string). (*Note Expression Patterns::.) d5733 2 a5734 1 PAT1 and the final record that matches PAT2. (*Note Ranges::.) d5738 3 a5740 2 Special patterns for you to supply startup or cleanup actions for your `awk' program. (*Note BEGIN/END::.) d5743 2 a5744 1 The empty pattern matches every input record. (*Note Empty::.) d5747 1 a5747 1 File: gawk.info, Node: Regexp Patterns, Next: Expression Patterns, Up: Pattern Overview d5752 2 a5753 2 Regular expressions are one of the first kinds of patterns presented in this book. This kind of pattern is simply a regexp constant in the d5766 16 a5781 12 Any `awk' expression is valid as an `awk' pattern. The pattern matches if the expression's value is nonzero (if a number) or non-null (if a string). The expression is reevaluated each time the rule is tested against a new input record. If the expression uses fields such as `$1', the value depends directly on the new input record's text; otherwise, it depends on only what has happened so far in the execution of the `awk' program. Comparison expressions, using the comparison operators described in *Note Typing and Comparison::, are a very common kind of pattern. Regexp matching and nonmatching are also very common expressions. The left operand of the `~' and `!~' operators is a string. The right d5783 6 a5788 4 (`/REGEXP/'), or any expression whose string value is used as a dynamic regular expression (*note Computed Regexps::). The following example prints the second field of each input record whose first field is precisely `foo': d5792 3 a5794 3 (There is no output, because there is no BBS site with the exact name `foo'.) Contrast this with the following regular expression match, which accepts any record with a first field that contains `foo': a5801 5 A regexp constant as a pattern is also a special case of an expression pattern. The expression `/foo/' has the value one if `foo' appears in the current input record. Thus, as a pattern, `/foo/' matches any record containing `foo'. d5804 4 a5807 2 match. For example, the following command prints all the records in `BBS-list' that contain both `2400' and `foo': d5813 1 a5813 1 _either_ `2400' or `foo' (or both, of course): d5824 2 a5825 2 The following command prints all records in `BBS-list' that do _not_ contain the string `foo': d5836 1 a5836 1 The subexpressions of a Boolean operator in a pattern can be d5839 1 a5839 1 inside Boolean patterns. Likewise, the special patterns `BEGIN' and d5841 6 a5846 1 cannot appear inside Boolean patterns. d5854 4 a5857 5 A "range pattern" is made of two patterns separated by a comma, in the form `BEGPAT, ENDPAT'. It is used to match ranges of consecutive input records. The first pattern, BEGPAT, controls where the range begins, while ENDPAT controls where the pattern ends. For example, the following: d5859 1 a5859 1 awk '$1 == "on", $1 == "off"' myfile d5861 1 a5861 1 prints every record in `myfile' between `on'/`off' pairs, inclusive. d5864 6 a5869 7 record. When a record matches BEGPAT, the range pattern is "turned on" and the range pattern matches this record as well. As long as the range pattern stays turned on, it automatically matches every input record read. The range pattern also matches ENDPAT against every input record; when this succeeds, the range pattern is turned off again for the following record. Then the range pattern goes back to checking BEGPAT against each record. d5876 6 a5881 5 It is possible for a pattern to be turned on and off by the same record. If the record satisfies both conditions, then the action is executed for just that record. For example, suppose there is text between two identical markers (e.g., the `%' symbol), each on its own line, that should be ignored. A first attempt would be to combine a d5883 4 a5886 3 statement (not discussed yet, *note Next Statement::). This causes `awk' to skip any further processing of the current record and start over again with the next input record. Such a program looks like this: d5892 2 a5893 3 turned off by the first line, which just has a `%' on it. To accomplish this task, write the program in the following manner, using a flag: d5898 3 a5900 3 In a range pattern, the comma (`,') has the lowest precedence of all the operators (i.e., it is evaluated last). Thus, the following program attempts to combine a range pattern with another, simpler test: d5904 4 a5907 9 The intent of this program is `(/1/,/2/) || /Yes/'. However, `awk' interprets this as `/1/, (/2/ || /Yes/)'. This cannot be changed or worked around; range patterns do not combine with other patterns: $ echo Yes | gawk '(/1/,/2/) || /Yes/' error--> gawk: cmd. line:1: (/1/,/2/) || /Yes/ error--> gawk: cmd. line:1: ^ parse error error--> gawk: cmd. line:2: (/1/,/2/) || /Yes/ error--> gawk: cmd. line:2: ^ unexpected newline d5915 3 a5917 7 All the patterns described so far are for matching input records. The `BEGIN' and `END' special patterns are different. They supply startup and cleanup actions for `awk' programs. `BEGIN' and `END' rules must have actions; there is no default action for these rules because there is no current record when they run. `BEGIN' and `END' rules are often referred to as "`BEGIN' and `END' blocks" by long-time `awk' programmers. d5925 1 a5925 1 File: gawk.info, Node: Using BEGIN/END, Next: I/O And BEGIN/END, Up: BEGIN/END d5930 3 a5932 3 A `BEGIN' rule is executed once only, before the first input record is read. Likewise, an `END' rule is executed once only, after all the input is read. For example: d5937 1 a5937 1 > END { print "\"foo\" appears", n, "times." }' BBS-list d5944 6 a5949 4 counter `n' to zero, since `awk' does this automatically (*note Variables::). The second rule increments the variable `n' every time a record containing the pattern `foo' is read. The `END' rule prints the value of `n' at the end of the run. d5952 5 a5956 4 with Boolean operators (indeed, they cannot be used with any operators). An `awk' program may have multiple `BEGIN' and/or `END' rules. They are executed in the order in which they appear: all the `BEGIN' rules at startup and all the `END' rules at termination. `BEGIN' and `END' d5958 5 a5962 6 the 1987 version of `awk' and is included in the POSIX standard. The original (1978) version of `awk' required the `BEGIN' rule to be placed at the beginning of the program, the `END' rule to be placed at the end, and only allowed one of each. This is no longer required, but it is a good idea to follow this template in terms of program organization and readability. d5965 17 a5981 16 functions, because each library file can have its own `BEGIN' and/or `END' rule to do its own initialization and/or cleanup. The order in which library functions are named on the command line controls the order in which their `BEGIN' and `END' rules are executed. Therefore, you have to be careful when writing such rules in library files so that the order in which they are executed doesn't matter. *Note Options::, for more information on using library functions. *Note Library Functions::, for a number of useful library functions. If an `awk' program has only a `BEGIN' rule and no other rules, then the program exits after the `BEGIN' rule is run.(1) However, if an `END' rule exists, then the input is read, even if there are no other rules in the program. This is necessary in case the `END' rule checks the `FNR' and `NR' variables. ---------- Footnotes ---------- d5983 2 a5984 2 (1) The original version of `awk' used to keep reading and ignoring input until the end of the file was seen. d5992 32 a6023 36 There are several (sometimes subtle) points to remember when doing I/O from a `BEGIN' or `END' rule. The first has to do with the value of `$0' in a `BEGIN' rule. Because `BEGIN' rules are executed before any input is read, there simply is no input record, and therefore no fields, when executing `BEGIN' rules. References to `$0' and the fields yield a null string or zero, depending upon the context. One way to give `$0' a real value is to execute a `getline' command without a variable (*note Getline::). Another way is simply to assign a value to `$0'. The second point is similar to the first but from the other direction. Traditionally, due largely to implementation issues, `$0' and `NF' were _undefined_ inside an `END' rule. The POSIX standard specifies that `NF' is available in an `END' rule. It contains the number of fields from the last input record. Most probably due to an oversight, the standard does not say that `$0' is also preserved, although logically one would think that it should be. In fact, `gawk' does preserve the value of `$0' for use in `END' rules. Be aware, however, that Unix `awk', and possibly other implementations, do not. The third point follows from the first two. The meaning of `print' inside a `BEGIN' or `END' rule is the same as always: `print $0'. If `$0' is the null string, then this prints an empty line. Many long time `awk' programmers use an unadorned `print' in `BEGIN' and `END' rules, to mean `print ""', relying on `$0' being null. Although one might generally get away with this in `BEGIN' rules, it is a very bad idea in `END' rules, at least in `gawk'. It is also poor style, since if an empty line is needed in the output, the program should print one explicitly. Finally, the `next' and `nextfile' statements are not allowed in a `BEGIN' rule, because the implicit read-a-record-and-match-against-the-rules loop has not started yet. Similarly, those statements are not valid in an `END' rule, since all the input has been read. (*Note Next Statement::, and see *Note Nextfile Statement::.) d6031 1 a6031 1 An empty (i.e., nonexistent) pattern is considered to match _every_ d6039 1 a6039 1 File: gawk.info, Node: Using Shell Variables, Next: Action Overview, Prev: Pattern Overview, Up: Patterns and Actions d6041 2 a6042 2 Using Shell Variables in Programs ================================= d6044 3 a6046 50 `awk' programs are often used as components in larger programs written in shell. For example, it is very common to use a shell variable to hold a pattern that the `awk' program searches for. There are two ways to get the value of the shell variable into the body of the `awk' program. The most common method is to use shell quoting to substitute the variable's value into the program inside the script. For example, in the following program: echo -n "Enter search pattern: " read pattern awk "/$pattern/ "'{ nmatches++ } END { print nmatches, "found" }' /path/to/data the `awk' program consists of two pieces of quoted text that are concatenated together to form the program. The first part is double-quoted, which allows substitution of the `pattern' variable inside the quotes. The second part is single-quoted. Variable substitution via quoting works, but can be potentially messy. It requires a good understanding of the shell's quoting rules (*note Quoting::), and it's often difficult to correctly match up the quotes when reading the program. A better method is to use `awk''s variable assignment feature (*note Assignment Options::) to assign the shell variable's value to an `awk' variable's value. Then use dynamic regexps to match the pattern (*note Computed Regexps::). The following shows how to redo the previous example using this technique: echo -n "Enter search pattern: " read pattern awk -v pat="$pattern" '$0 ~ pat { nmatches++ } END { print nmatches, "found" }' /path/to/data Now, the `awk' program is just one single-quoted string. The assignment `-v pat="$pattern"' still requires double quotes, in case there is whitespace in the value of `$pattern'. The `awk' variable `pat' could be named `pattern' too, but that would be more confusing. Using a variable also provides more flexibility, since the variable can be used anywhere inside the program--for printing, as an array subscript, or for any other use--without requiring the quoting tricks at every point in the program.  File: gawk.info, Node: Action Overview, Next: Statements, Prev: Using Shell Variables, Up: Patterns and Actions Actions ======= d6048 4 a6051 6 An `awk' program or script consists of a series of rules and function definitions interspersed. (Functions are described later. *Note User-defined::.) A rule contains a pattern and an action, either of which (but not both) may be omitted. The purpose of the "action" is to tell `awk' what to do once a match for the pattern is found. Thus, in outline, an `awk' program generally looks like this: d6060 7 a6066 6 curly braces (`{...}'). Each statement specifies one thing to do. The statements are separated by newlines or semicolons. The curly braces around an action must be used even if the action contains only one statement, or if it contains no statements at all. However, if you omit the action entirely, omit the curly braces as well. An omitted action is equivalent to `{ print $0 }': d6068 2 a6069 2 /foo/ { } match `foo', do nothing -- empty action /foo/ match `foo', print the record -- omitted action d6071 1 a6071 1 The following types of statements are supported in `awk': d6073 20 a6092 20 Expressions Call functions or assign values to variables (*note Expressions::). Executing this kind of statement simply computes the value of the expression. This is useful when the expression has side effects (*note Assignment Ops::). Control statements Specify the control flow of `awk' programs. The `awk' language gives you C-like constructs (`if', `for', `while', and `do') as well as a few special ones (*note Statements::). Compound statements Consist of one or more statements enclosed in curly braces. A compound statement is used in order to put several statements together in the body of an `if', `while', `do', or `for' statement. Input statements Use the `getline' command (*note Getline::). Also supplied in `awk' are the `next' statement (*note Next Statement::), and the `nextfile' statement (*note Nextfile Statement::). d6094 2 a6095 2 Output statements Such as `print' and `printf'. *Note Printing::. d6097 2 a6098 2 Deletion statements For deleting array elements. *Note Delete::. d6101 1 a6101 1 File: gawk.info, Node: Statements, Next: Built-in Variables, Prev: Action Overview, Up: Patterns and Actions d6104 1 a6104 1 ============================= d6106 1 a6106 1 "Control statements", such as `if', `while', and so on, control the d6110 9 a6118 7 All the control statements start with special keywords, such as `if' and `while', to distinguish them from simple expressions. Many control statements contain other statements. For example, the `if' statement contains another statement that may or may not be executed. The contained statement is called the "body". To include more than one statement in the body, group them into a single "compound statement" with curly braces, separating them with newlines or semicolons. a6128 2 * Switch Statement:: Switch/case evaluation for conditional execution of statements based on a value. d6137 1 a6137 1 File: gawk.info, Node: If Statement, Next: While Statement, Up: Statements d6140 1 a6140 1 ------------------------- d6148 1 a6148 1 statement does. If the CONDITION is true, THEN-BODY is executed; d6151 3 a6153 2 the null string; otherwise, the condition is true. Refer to the following: d6160 1 a6160 1 In this example, if the expression `x % 2 == 0' is true (that is, if d6162 7 a6168 5 statement is executed; otherwise, the second `print' statement is executed. If the `else' keyword appears on the same line as THEN-BODY and THEN-BODY is not a compound statement (i.e., not surrounded by curly braces), then a semicolon must separate THEN-BODY from the `else'. To illustrate this, the previous example can be rewritten as: d6173 6 a6178 4 If the `;' is left out, `awk' can't interpret the statement and it produces a syntax error. Don't actually write programs this way, because a human reader might fail to see the `else' if it is not the first thing on its line. d6184 4 a6187 1 --------------------- d6189 3 a6191 4 In programming, a "loop" is a part of a program that can be executed two or more times in succession. The `while' statement is the simplest looping statement in `awk'. It repeatedly executes a statement as long as a condition is true. For example: d6196 5 a6200 3 BODY is a statement called the "body" of the loop, and CONDITION is an expression that controls how long the loop keeps running. The first thing the `while' statement does is test the CONDITION. If the d6202 1 a6202 1 true when the value is not zero and not a null string.) After BODY has d6204 6 a6209 5 is executed again. This process repeats until the CONDITION is no longer true. If the CONDITION is initially false, the body of the loop is never executed and `awk' continues with the statement following the loop. This example prints the first three fields of each record, one per line: d6218 14 a6231 13 The body of this loop is a compound statement enclosed in braces, containing two statements. The loop works in the following manner: first, the value of `i' is set to one. Then, the `while' statement tests whether `i' is less than or equal to three. This is true when `i' equals one, so the `i'-th field is printed. Then the `i++' increments the value of `i' and the loop repeats. The loop terminates when `i' reaches four. A newline is not required between the condition and the body; however using one makes the program clearer unless the body is a compound statement or else is very simple. The newline after the open-brace that begins the compound statement is not required either, but the program is harder to read without it. d6237 1 a6237 1 -------------------------- d6240 2 a6241 2 `do' loop executes the BODY once and then repeats the BODY as long as the CONDITION is true. It looks like this: d6247 2 a6248 2 Even if the CONDITION is false at the start, the BODY is executed at least once (and only once, unless executing BODY makes CONDITION true). d6254 4 a6257 2 This statement does not execute BODY even once if the CONDITION is false to begin with. The following is an example of a `do' statement: d6259 1 a6259 1 { i = 1 d6264 1 a6264 1 } d6266 4 a6269 4 This program prints each input record 10 times. However, it isn't a very realistic example, since in this case an ordinary `while' would do just as well. This situation reflects actual experience; only occasionally is there a real use for a `do' statement. d6272 1 a6272 1 File: gawk.info, Node: For Statement, Next: Switch Statement, Prev: Do Statement, Up: Statements d6275 1 a6275 1 ------------------- d6283 1 a6283 1 The INITIALIZATION, CONDITION, and INCREMENT parts are arbitrary `awk' d6287 2 a6288 2 long as the CONDITION is true, it repeatedly executes BODY and then INCREMENT. Typically, INITIALIZATION sets a variable to either zero or d6290 3 a6292 1 desired number of iterations. For example: d6298 2 a6299 2 This prints the first three fields of each input record, with one field per line. d6301 15 a6315 16 It isn't possible to set more than one variable in the INITIALIZATION part without using a multiple assignment statement such as `x = y = 0'. This makes sense only if all the initial values are equal. (But it is possible to initialize additional variables by writing their assignments as separate statements preceding the `for' loop.) The same is true of the INCREMENT part. Incrementing additional variables requires separate statements at the end of the loop. The C compound expression, using C's comma operator, is useful in this context but it is not supported in `awk'. Most often, INCREMENT is an increment expression, as in the previous example. But this is not required; it can be any expression whatsoever. For example, the following statement prints all the powers of two between 1 and 100: d6320 2 a6321 2 If there is nothing to be done, any of the three expressions in the parentheses following the `for' keyword may be omitted. Thus, d6323 2 a6324 2 omitted, it is treated as true, effectively yielding an "infinite loop" (i.e., a loop that never terminates). d6335 4 a6338 10 The only exception is when the `continue' statement (*note Continue Statement::) is used inside the loop. Changing a `for' statement to a `while' statement in this way can change the effect of the `continue' statement inside the loop. The `awk' language has a `for' statement in addition to a `while' statement because a `for' loop is often both less work to type and more natural to think of. Counting the number of iterations is very common in loops. It can be easier to think of this counting as part of looping rather than as something to do inside the loop. d6346 2 a6347 2 *Note Scanning an Array::, for more information on this version of the `for' loop. d6349 5 a6353 5  File: gawk.info, Node: Switch Statement, Next: Break Statement, Prev: For Statement, Up: Statements The `switch' Statement ---------------------- d6355 1 a6355 47 *NOTE:* This node describes an experimental feature added in `gawk' 3.1.3. It is _not_ enabled by default. To enable it, use the `--enable-switch' option to `configure' when `gawk' is being configured and built. *Note Additional Configuration Options::, for more information. The `switch' statement allows the evaluation of an expression and the execution of statements based on a `case' match. Case statements are checked for a match in the order they are defined. If no suitable `case' is found, the `default' section is executed, if supplied. The general form of the `switch' statement looks like this: switch (EXPRESSION) { case VALUE OR REGULAR EXPRESSION: CASE-BODY default: DEFAULT-BODY } The `switch' statement works as it does in C. Once a match to a given case is made, case statement bodies are executed until a `break', `continue', `next', `nextfile' or `exit' is encountered, or the end of the `switch' statement itself. For example: switch (NR * 2 + 1) { case 3: case "11": print NR - 1 break case /2[[:digit:]]+/: print NR default: print NR + 1 case -1: print NR * -1 } Note that if none of the statements specified above halt execution of a matched `case' statement, execution falls through to the next `case' until execution halts. In the above example, for any case value starting with `2' followed by one or more digits, the `print' statement is executed and then falls through into the `default' section, executing its `print' statement. In turn, the -1 case will also be executed since the `default' does not halt execution. d6358 1 a6358 1 File: gawk.info, Node: Break Statement, Next: Continue Statement, Prev: Switch Statement, Up: Statements d6361 1 a6361 1 --------------------- d6367 10 a6376 11 # find smallest divisor of num { num = $1 for (div = 2; div*div <= num; div++) if (num % div == 0) break if (num % div == 0) printf "Smallest divisor of %d is %d\n", num, div else printf "%d is prime\n", num } d6382 2 a6383 2 statement, which stops the entire `awk' program. *Note Exit Statement::.) d6385 17 a6401 2 Th following program illustrates how the CONDITION of a `for' or `while' statement could be replaced with a `break' inside an `if': d6403 8 a6410 22 # find smallest divisor of num { num = $1 for (div = 2; ; div++) { if (num % div == 0) { printf "Smallest divisor of %d is %d\n", num, div break } if (div*div > num) { printf "%d is prime\n", num break } } } The `break' statement has no meaning when used outside the body of a loop. However, although it was never documented, historical implementations of `awk' treated the `break' statement outside of a loop as if it were a `next' statement (*note Next Statement::). Recent versions of Unix `awk' no longer allow this usage. `gawk' supports this use of `break' only if `--traditional' has been specified on the command line (*note Options::). Otherwise, it is treated as an error, d6412 1 a6412 1 inside the body of a loop. (d.c.) d6418 1 a6418 1 ------------------------ d6420 1 a6420 1 As with `break', the `continue' statement is used only inside `for', d6426 1 a6426 1 rest of the body of the loop and resume execution with the d6430 1 a6430 1 BEGIN { d6437 1 a6437 1 } d6439 4 a6442 4 This program prints all the numbers from 0 to 20--except for 5, for which the `printf' is skipped. Because the increment `x++' is not skipped, `x' does not remain stuck at 5. Contrast the `for' loop from the previous example with the following `while' loop: d6444 1 a6444 1 BEGIN { d6453 1 a6453 1 } d6455 1 a6455 1 This program loops forever once `x' reaches 5. d6457 10 a6466 9 The `continue' statement has no meaning when used outside the body of a loop. Historical versions of `awk' treated a `continue' statement outside a loop the same way they treated a `break' statement outside a loop: as if it were a `next' statement (*note Next Statement::). Recent versions of Unix `awk' no longer work this way, and `gawk' allows it only if `--traditional' is specified on the command line (*note Options::). Just like the `break' statement, the POSIX standard specifies that `continue' should only be used inside the body of a loop. (d.c.) d6472 1 a6472 1 -------------------- d6476 2 a6477 2 further rules are executed for the current record, and the rest of the current rule's action isn't executed. d6480 4 a6483 3 Getline::). That also causes `awk' to read the next record immediately, but it does not alter the flow of control in any way (i.e., the rest of the current action executes with a new input record). d6488 2 a6489 2 then the `next' statement is analogous to a `continue' statement. It skips to the end of the body of this implicit loop and executes the d6492 3 a6494 4 For example, suppose an `awk' program works only on records with four fields, and it shouldn't fail when given bad input. To avoid complicating the rest of the program, write a "weed out" rule near the beginning, in the following manner: d6502 3 a6504 4 Because of the `next' statement, the program's subsequent rules won't see the bad record. The error message is redirected to the standard error output stream, as error messages should be. For more detail see *Note Special Files::. d6507 2 a6508 2 `next' statement is used in a `BEGIN' or `END' rule. `gawk' treats it as a syntax error. Although POSIX permits it, some other `awk' d6510 12 a6521 5 (*note User-defined::). Just as with any other `next' statement, a `next' statement inside a function body reads the next record and starts processing it with the first rule in the program. If the `next' statement causes the end of the input to be reached, then the code in any `END' rules is executed. *Note BEGIN/END::. d6526 2 a6527 2 Using `gawk''s `nextfile' Statement ----------------------------------- a6533 4 The `nextfile' statement is a `gawk' extension. In most other `awk' implementations, or if `gawk' is in compatibility mode (*note Options::), `nextfile' is not special. d6537 16 a6552 27 the first rule in the program. (`ARGIND' hasn't been introduced yet. *Note Built-in Variables::.) If the `nextfile' statement causes the end of the input to be reached, then the code in any `END' rules is executed. *Note BEGIN/END::. The `nextfile' statement is useful when there are many data files to process but it isn't necessary to process every record in every file. Normally, in order to move on to the next data file, a program has to continue scanning the unwanted records. The `nextfile' statement accomplishes this much more efficiently. While one might think that `close(FILENAME)' would accomplish the same as `nextfile', this isn't true. `close' is reserved for closing files, pipes, and coprocesses that are opened with redirections. It is not related to the main processing that `awk' does with the files listed in `ARGV'. If it's necessary to use an `awk' version that doesn't support `nextfile', see *Note Nextfile Function::, for a user-defined function that simulates the `nextfile' statement. The current version of the Bell Laboratories `awk' (*note Other Versions::) also supports `nextfile'. However, it doesn't allow the `nextfile' statement inside function bodies (*note User-defined::). `gawk' does; a `nextfile' inside a function body reads the next record and starts processing it with the first rule in the program, just as any other `nextfile' statement. d6555 6 a6560 5 file') for the `nextfile' statement. In version 3.0, this was changed to one word, because the treatment of `file' was inconsistent. When it appeared after `next', `file' was a keyword; otherwise, it was a regular identifier. The old usage is no longer accepted; `next file' generates a syntax error. d6566 1 a6566 1 -------------------- d6570 1 a6570 1 ignored. The `exit' statement is written as follows: d6574 7 a6580 6 When an `exit' statement is executed from a `BEGIN' rule, the program stops processing everything immediately. No input records are read. However, if an `END' rule is present, as part of executing the `exit' statement, the `END' rule is executed (*note BEGIN/END::). If `exit' is used as part of an `END' rule, it causes the program to stop immediately. d6587 4 a6590 4 In such a case, if you don't want the `END' rule to do its job, set a variable to nonzero before the `exit' statement and check that variable in the `END' rule. *Note Assert Function::, for an example that does this. d6596 2 a6597 2 second time from an `END' rule with no argument, `awk' uses the previously supplied exit value. (d.c.) d6599 4 a6602 4 For example, suppose an error condition occurs that is difficult or impossible to handle. Conventionally, programs report this by exiting with a nonzero status. An `awk' program can do this using an `exit' statement with a nonzero argument, as shown in the following example: d6605 1 a6605 1 if (("date" | getline date_now) <= 0) { d6614 1 a6614 1 File: gawk.info, Node: Built-in Variables, Prev: Statements, Up: Patterns and Actions d6617 1 a6617 1 ================== d6619 8 a6626 8 Most `awk' variables are available to use for your own purposes; they never change unless your program assigns values to them, and they never affect anything unless your program examines them. However, a few variables in `awk' have special built-in meanings. `awk' examines some of these automatically, so that they enable you to tell `awk' how to do certain things. Others are set automatically by `awk', so that they carry information from the internal workings of `awk' to your program. d6628 2 a6629 2 This minor node documents all the built-in variables of `gawk', most of which are also documented in the chapters describing their areas of d6636 2 a6637 2 * Auto-set:: Built-in variables where `awk' gives you information. d6641 1 a6641 1 File: gawk.info, Node: User-modified, Next: Auto-set, Up: Built-in Variables d6643 2 a6644 2 Built-in Variables That Control `awk' ------------------------------------- d6646 3 a6648 19 The following is an alphabetical list of variables that you can change to control how `awk' does certain things. The variables that are specific to `gawk' are marked with a pound sign (`#'). `BINMODE #' On non-POSIX systems, this variable specifies use of binary mode for all I/O. Numeric values of one, two, or three specify that input files, output files, or all files, respectively, should use binary I/O. Alternatively, string values of `"r"' or `"w"' specify that input files and output files, respectively, should use binary I/O. A string value of `"rw"' or `"wr"' indicates that all files should use binary I/O. Any other string value is equivalent to `"rw"', but `gawk' generates a warning message. `BINMODE' is described in more detail in *Note PC Using::. This variable is a `gawk' extension. In other `awk' implementations (except `mawk', *note Other Versions::), or if `gawk' is in compatibility mode (*note Options::), it is not special. d6652 17 a6668 14 Conversion::). It works by being passed, in effect, as the first argument to the `sprintf' function (*note String Functions::). Its default value is `"%.6g"'. `CONVFMT' was introduced by the POSIX standard. `FIELDWIDTHS #' This is a space-separated list of columns that tells `gawk' how to split input with fixed columnar boundaries. Assigning a value to `FIELDWIDTHS' overrides the use of `FS' for field splitting. *Note Constant Size::, for more information. If `gawk' is in compatibility mode (*note Options::), then `FIELDWIDTHS' has no special meaning, and field-splitting operations occur based exclusively on the value of `FS'. d6671 6 a6676 7 This is the input field separator (*note Field Separators::). The value is a single-character string or a multi-character regular expression that matches the separations between fields in an input record. If the value is the null string (`""'), then each character in the record becomes a separate field. (This behavior is a `gawk' extension. POSIX `awk' does not specify the behavior when `FS' is the null string.) d6689 18 a6706 36 If `gawk' is using `FIELDWIDTHS' for field splitting, assigning a value to `FS' causes `gawk' to return to the normal, `FS'-based field splitting. An easy way to do this is to simply say `FS = FS', perhaps with an explanatory comment. `IGNORECASE #' If `IGNORECASE' is nonzero or non-null, then all string comparisons and all regular expression matching are case independent. Thus, regexp matching with `~' and `!~', as well as the `gensub', `gsub', `index', `match', `split', and `sub' functions, record termination with `RS', and field splitting with `FS', all ignore case when doing their particular regexp operations. However, the value of `IGNORECASE' does _not_ affect array subscripting and it does not affect field splitting when using a single-character field separator. *Note Case-sensitivity::. If `gawk' is in compatibility mode (*note Options::), then `IGNORECASE' has no special meaning. Thus, string and regexp operations are always case-sensitive. `LINT #' When this variable is true (nonzero or non-null), `gawk' behaves as if the `--lint' command-line option is in effect. (*note Options::). With a value of `"fatal"', lint warnings become fatal errors. With a value of `"invalid"', only warnings about things that are actually invalid are issued. (This is not fully implemented yet.) Any other true value prints nonfatal warnings. Assigning a false value to `LINT' turns off the lint warnings. This variable is a `gawk' extension. It is not special in other `awk' implementations. Unlike the other special variables, changing `LINT' does affect the production of lint warnings, even if `gawk' is in compatibility mode. Much as the `--lint' and `--traditional' options independently control different aspects of `gawk''s behavior, the control of lint warnings during program execution is independent of the flavor of `awk' being executed. d6710 7 a6716 6 Conversion::) for printing with the `print' statement. It works by being passed as the first argument to the `sprintf' function (*note String Functions::). Its default value is `"%.6g"'. Earlier versions of `awk' also used `OFMT' to specify the format for converting numbers to strings in general expressions; this is now done by `CONVFMT'. d6719 3 a6721 3 This is the output field separator (*note Output Separators::). It is output between the fields printed by a `print' statement. Its default value is `" "', a string consisting of a single space. d6725 2 a6726 2 every `print' statement. Its default value is `"\n"', the newline character. (*Note Output Separators::.) d6733 3 a6735 7 blank lines. If it is a regexp, records are separated by matches of the regexp in the input text. (*Note Records::.) The ability for `RS' to be a regular expression is a `gawk' extension. In most other `awk' implementations, or if `gawk' is in compatibility mode (*note Options::), just the first character of `RS''s value is used. d6738 5 a6742 16 This is the subscript separator. It has the default value of `"\034"' and is used to separate the parts of the indices of a multidimensional array. Thus, the expression `foo["A", "B"]' really accesses `foo["A\034B"]' (*note Multi-dimensional::). `TEXTDOMAIN #' This variable is used for internationalization of programs at the `awk' level. It sets the default text domain for specially marked string constants in the source text, as well as for the `dcgettext', `dcngettext' and `bindtextdomain' functions (*note Internationalization::). The default value of `TEXTDOMAIN' is `"messages"'. This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note Options::), it is not special. d6746 1 a6746 1 (1) In POSIX `awk', newline does not count as whitespace. d6751 2 a6752 2 Built-in Variables That Convey Information ------------------------------------------ d6754 4 a6757 4 The following is an alphabetical list of variables that `awk' sets automatically on certain occasions in order to provide information to your program. The variables that are specific to `gawk' are marked with a pound sign (`#'). d6759 2 a6760 1 `ARGC, ARGV' d6763 3 a6765 3 arguments present. *Note Other Arguments::. Unlike most `awk' arrays, `ARGV' is indexed from 0 to `ARGC' - 1. In the following example: d6768 2 a6769 2 > for (i = 0; i < ARGC; i++) > print ARGV[i] d6775 1 a6775 1 `ARGV[0]' contains `"awk"', `ARGV[1]' contains d6778 1 a6778 1 element in `ARGV', because the elements are numbered from zero. d6781 4 a6784 7 the array from 0 to `ARGC' - 1, are derived from the C language's method of accessing command-line arguments. The value of `ARGV[0]' can vary from system to system. Also, you should note that the program text is _not_ included in `ARGV', nor are any of `awk''s command-line options. *Note ARGC and ARGV::, for information about how `awk' uses these variables. d6786 1 a6786 1 `ARGIND #' d6790 2 a6791 2 processing the input files, `FILENAME == ARGV[ARGIND]' is always true. d6794 2 a6795 2 how far along you are in the list of data files as well as to distinguish between successive instances of the same file name on d6799 2 a6800 2 program, `gawk' automatically sets it to a new value when the next file is opened. d6802 1 a6802 1 This variable is a `gawk' extension. In other `awk' d6804 1 a6804 1 Options::), it is not special. d6808 1 a6808 1 The array indices are the environment variable names; the elements d6813 1 d6817 1 a6817 1 `ENVIRON["AWKPATH"]', *note AWKPATH Variable::). d6819 2 a6820 2 `ERRNO #' If a system error occurs during a redirection for `getline', d6822 1 a6822 1 `ERRNO' contains a string describing the error. d6824 1 a6824 1 This variable is a `gawk' extension. In other `awk' d6826 1 a6826 1 Options::), it is not special. d6829 7 a6835 8 The name of the file that `awk' is currently reading. When no data files are listed on the command line, `awk' reads from the standard input and `FILENAME' is set to `"-"'. `FILENAME' is changed each time a new file is read (*note Reading Files::). Inside a `BEGIN' rule, the value of `FILENAME' is `""', since there are no input files being processed yet.(1) (d.c.) Note, though, that using `getline' (*note Getline::) inside a `BEGIN' rule can give `FILENAME' a value. d6838 4 a6841 3 The current record number in the current file. `FNR' is incremented each time a new record is read (*note Getline::). It is reinitialized to zero each time a new input file is started. d6844 3 a6846 9 The number of fields in the current input record. `NF' is set each time a new record is read, when a new field is created or when `$0' changes (*note Fields::). Unlike most of the variables described in this node, assigning a value to `NF' has the potential to affect `awk''s internal workings. In particular, assignments to `NF' can be used to create or remove fields from the current record: *Note Changing Fields::. d6849 4 a6852 43 The number of input records `awk' has processed since the beginning of the program's execution (*note Records::). `NR' is incremented each time a new record is read. `PROCINFO #' The elements of this array provide access to information about the running `awk' program. The following elements (listed alphabetically) are guaranteed to be available: `PROCINFO["egid"]' The value of the `getegid' system call. `PROCINFO["euid"]' The value of the `geteuid' system call. `PROCINFO["FS"]' This is `"FS"' if field splitting with `FS' is in effect, or it is `"FIELDWIDTHS"' if field splitting with `FIELDWIDTHS' is in effect. `PROCINFO["gid"]' The value of the `getgid' system call. `PROCINFO["pgrpid"]' The process group ID of the current process. `PROCINFO["pid"]' The process ID of the current process. `PROCINFO["ppid"]' The parent process ID of the current process. `PROCINFO["uid"]' The value of the `getuid' system call. On some systems, there may be elements in the array, `"group1"' through `"groupN"' for some N. N is the number of supplementary groups that the process has. Use the `in' operator to test for these elements (*note Reference to Elements::). This array is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note Options::), it is not special. d6855 5 a6859 4 The length of the substring matched by the `match' function (*note String Functions::). `RLENGTH' is set by invoking the `match' function. Its value is the length of the matched string, or -1 if no match is found. d6862 5 a6866 5 The start-index in characters of the substring that is matched by the `match' function (*note String Functions::). `RSTART' is set by invoking the `match' function. Its value is the position of the string where the matched substring starts, or zero if no match was found. d6868 2 a6869 2 `RT #' This is set each time a record is read. It contains the input text d6872 1 a6872 1 This variable is a `gawk' extension. In other `awk' d6874 1 a6874 4 Options::), it is not special. Advanced Notes: Changing `NR' and `FNR' --------------------------------------- d6876 5 a6880 5 `awk' increments `NR' and `FNR' each time it reads a record, instead of setting them to the absolute value of the number of records read. This means that a program can change these variables and their new values are incremented for each record. (d.c.) This is demonstrated in the following example: d6892 4 a6895 3 Before `FNR' was added to the `awk' language (*note V7/SVR3.1::), many `awk' programs used this feature to track the number of records in a file by resetting `NR' to zero when `FILENAME' changed. d6899 1 a6899 1 (1) Some early implementations of Unix `awk' initialized `FILENAME' d6901 1 a6901 1 was incorrect and should not be relied upon in your programs. d6907 1 a6907 1 ----------------------- d6909 3 a6911 2 *Note Auto-set::, presented the following program describing the information contained in `ARGC' and `ARGV': d6921 7 a6927 21 In this example, `ARGV[0]' contains `awk', `ARGV[1]' contains `inventory-shipped', and `ARGV[2]' contains `BBS-list'. Notice that the `awk' program is not entered in `ARGV'. The other special command-line options, with their arguments, are also not entered. This includes variable assignments done with the `-v' option (*note Options::). Normal variable assignments on the command line _are_ treated as arguments and do show up in the `ARGV' array: $ cat showargs.awk -| BEGIN { -| printf "A=%d, B=%d\n", A, B -| for (i = 0; i < ARGC; i++) -| printf "\tARGV[%d] = %s\n", i, ARGV[i] -| } -| END { printf "A=%d, B=%d\n", A, B } $ awk -v A=1 -f showargs.awk B=2 /dev/null -| A=1, B=0 -| ARGV[0] = awk -| ARGV[1] = B=2 -| ARGV[2] = /dev/null -| A=1, B=2 d6929 1 a6929 1 A program can alter `ARGC' and the elements of `ARGV'. Each time d6932 4 a6935 3 string there, a program can change which files are read. Use `"-"' to represent the standard input. Storing additional elements and incrementing `ARGC' causes additional files to be read. d6937 1 a6937 1 If the value of `ARGC' is decreased, that eliminates input files d6939 1 a6939 1 elsewhere, a program can treat the eliminated arguments as something d6945 2 a6946 2 string. Another option is to use the `delete' statement to remove elements from `ARGV' (*note Delete::). d6948 8 a6955 5 All of these actions are typically done in the `BEGIN' rule, before actual processing of the input begins. *Note Split Program::, and see *Note Tee Program::, for examples of each way of removing elements from `ARGV'. The following fragment processes `ARGV' in order to examine, and then remove, command-line options: d6973 2 a6974 3 To actually get the options into the `awk' program, end the `awk' options with `--' and then supply the `awk' program's options, in the following manner: d6978 1 a6978 1 This is not necessary in `gawk'. Unless `--posix' has been d6980 5 a6984 3 for the `awk' program to deal with. As soon as it sees an unknown option, `gawk' stops looking for other options that it might otherwise recognize. The previous example with `gawk' would be: d6988 2 a6989 2 Because `-d' is not a valid `gawk' option, it and the following `-v' are passed on to the `awk' program. d6992 1 a6992 1 File: gawk.info, Node: Arrays, Next: Functions, Prev: Patterns and Actions, Up: Top d6997 1 a6997 1 An "array" is a table of values called "elements". The elements of d6999 4 a7002 13 numbers or strings. This major node describes how arrays work in `awk', how to use array elements, how to scan through every element in an array, and how to remove array elements. It also describes how `awk' simulates multidimensional arrays, as well as some of the less obvious points about array usage. The major node finishes with a discussion of `gawk''s facility for sorting an array based on its indices. `awk' maintains a single set of names that may be used for naming variables, arrays, and functions (*note User-defined::). Thus, you cannot have a variable and an array with the same name in the same `awk' program. d7018 1 a7018 1 * Multi-dimensional:: Emulating multidimensional arrays in d7020 1 a7020 2 * Multi-scanning:: Scanning multidimensional arrays. * Array Sorting:: Sorting array values and indices. d7023 1 a7023 1 File: gawk.info, Node: Array Intro, Next: Reference to Elements, Up: Arrays d7028 7 a7034 6 The `awk' language provides one-dimensional arrays for storing groups of related strings or numbers. Every `awk' array must have a name. Array names have the same syntax as variable names; any valid variable name would also be a valid array name. But one name cannot be used in both ways (as an array and as a variable) in the same `awk' program. d7037 20 a7056 22 languages, but there are fundamental differences. In `awk', it isn't necessary to specify the size of an array before starting to use it. Additionally, any number or string in `awk', not just consecutive integers, may be used as an array index. In most other languages, arrays must be "declared" before use, including a specification of how many elements or components they contain. In such languages, the declaration causes a contiguous block of memory to be allocated for that many elements. Usually, an index in the array must be a positive integer. For example, the index zero specifies the first element in the array, which is actually stored at the beginning of the block of memory. Index one specifies the second element, which is stored in memory right after the first element, and so on. It is impossible to add more elements to the array, because it has room only for as many elements as given in the declaration. (Some languages allow arbitrary starting and ending indices--e.g., `15 .. 27'--but the size of the array is still fixed when the array is declared.) A contiguous array of four elements might look like the following example, conceptually, if the element values are 8, `"foo"', `""', and 30: d7059 1 a7059 1 | 8 | "foo" | "" | 30 | Value d7061 1 a7061 1 0 1 2 3 Index d7064 2 a7065 2 the values. Here, 8 is the value at index zero, because 8 appears in the position with zero elements before it. d7067 8 a7074 8 Arrays in `awk' are different--they are "associative". This means that each array is a collection of pairs: an index and its corresponding array element value: Element 3 Value 30 Element 1 Value "foo" Element 0 Value 8 Element 2 Value "" d7076 2 a7077 1 The pairs are shown in jumbled order because their order is irrelevant. d7080 2 a7081 2 at any time. For example, suppose a tenth element is added to the array whose value is `"number ten"'. The result is: d7084 7 a7090 8 Element 3 Value 30 Element 1 Value "foo" Element 0 Value 8 Element 2 Value "" Now the array is "sparse", which just means some indices are missing. It has elements 0-3 and 10, but doesn't have elements 4, 5, 6, 7, 8, or 9. d7094 2 a7095 2 index. For example, the following is an array that translates words from English to French: d7104 3 a7106 4 numbers and strings as indices. In fact, array subscripts are always strings; this is discussed in more detail in *Note Numeric Array Subscripts::. Here, the number `1' isn't double-quoted, since `awk' automatically converts it to a string. d7109 2 a7110 4 The identical string value used to store an array element must be used to retrieve it. When `awk' creates an array (e.g., with the `split' built-in function), that array's indices are consecutive integers starting at one. (*Note String Functions::.) d7112 3 a7114 2 `awk''s arrays are efficient--the time to access an element is independent of the number of elements in the array. d7122 2 a7123 2 The principal way to use an array is to refer to one of its elements. An array reference is an expression as follows: d7128 1 a7128 1 of the desired element of the array. d7134 7 a7140 6 A reference to an array element that has no recorded value yields a value of `""', the null string. This includes elements that have not been assigned any value as well as elements that have been deleted (*note Delete::). Such a reference automatically creates that array element, with the null string as its value. (In some cases, this is unfortunate, because it might waste memory inside `awk'.) d7142 2 a7143 2 To determine whether an element exists in an array at a certain index, use the following expression: d7147 7 a7153 5 This expression tests whether the particular index exists, without the side effect of creating that element if it is not present. The expression has the value one (true) if `ARRAY[INDEX]' exists and zero (false) if it does not exist. For example, this statement tests whether the array `frequencies' contains the index `2': d7158 5 a7162 4 Note that this is _not_ a test of whether the array `frequencies' contains an element whose _value_ is two. There is no way to do that except to scan all the elements. Also, this _does not_ create `frequencies[2]', while the following (incorrect) alternative does: d7173 2 a7174 1 Array elements can be assigned values just like `awk' variables: d7178 4 a7181 3 ARRAY is the name of an array. The expression SUBSCRIPT is the index of the element of the array that is assigned a value. The expression VALUE is the value to assign to that element of the array. d7191 1 a7191 1 numbers are not in order when they are first read--instead they are d7193 4 a7196 4 line numbers as subscripts. The program then prints out the lines in sorted order of their numbers. It is a very simple program and gets confused upon encountering repeated numbers, gaps, or lines that don't begin with a number: d7211 6 a7216 3 line's number. The second rule runs after all the input has been read, to print out all the lines. When this program is run with the following input: d7224 1 a7224 1 Its output is: d7233 4 a7236 2 overrides the others. Gaps in the line numbers can be handled with an easy improvement to the program's `END' rule, as follows: d7250 7 a7256 7 In programs that use arrays, it is often necessary to use a loop that executes once for each element of an array. In other languages, where arrays are contiguous and indices are limited to positive integers, this is easy: all the valid indices can be found by counting from the lowest index up to the highest. This technique won't do the job in `awk', because any number or string can be an array index. So `awk' has a special kind of `for' statement for scanning an array: d7261 1 a7261 1 This loop executes BODY once for each index in ARRAY that the program d7264 1 a7264 1 The following program uses this form of the `for' statement. The d7269 3 a7271 3 word that is more than 10 characters long and also prints the number of such words. *Note String Functions::, for more information on the built-in function `length'. d7273 1 a7273 1 # Record a 1 for each word that is used at least once d7279 1 a7279 1 # Find number of distinct words more than 10 characters long d7289 2 a7290 1 *Note Word Sorting::, for a more detailed example of this type. d7296 3 a7298 3 the loop body; it is not predictable whether the `for' loop will reach them. Similarly, changing VAR inside the loop may produce strange results. It is best to avoid such things. d7306 1 a7306 1 To remove an individual element of an array, use the `delete' d7311 5 a7315 4 Once an array element has been deleted, any value the element once had is no longer available. It is as if the element had never been referred to or had been given a value. The following is an example of deleting elements in an array: d7321 4 a7324 3 Once an element is deleted, a subsequent `for' statement to scan the array does not report that element and the `in' operator to check for the presence of that element returns zero (i.e., false): d7330 2 a7331 2 It is important to note that deleting an element is _not_ the same as assigning it a null value (the empty string, `""'). For example: d7337 1 a7337 4 It is not an error to delete an element that does not exist. If `--lint' is provided on the command line (*note Options::), `gawk' issues a warning message when an element that is not in the array is deleted. d7339 2 a7340 2 All the elements of an array may be deleted with a single statement by leaving off the subscript in the `delete' statement, as follows: d7345 1 a7345 1 compatibility mode (*note Options::). d7351 2 a7352 2 The following statement provides a portable but nonobvious way to clear out an array:(1) d7354 1 d7357 5 a7361 14 The `split' function (*note String Functions::) clears out the target array first. This call asks it to split apart the null string. Because there is no data to split out, the function simply clears the array and then returns. *Caution:* Deleting an array does not change its type; you cannot delete an array and then use the array's name as a scalar (i.e., a regular variable). For example, the following does not work: a[1] = 3; delete a; a = 3 ---------- Footnotes ---------- (1) Thanks to Michael Brennan for pointing this out. d7369 8 a7376 6 An important aspect about arrays to remember is that _array subscripts are always strings_. When a numeric value is used as a subscript, it is converted to a string value before being used for subscripting (*note Conversion::). This means that the value of the built-in variable `CONVFMT' can affect how your program accesses elements of an array. For example: d7389 10 a7398 11 `CONVFMT', `"%.6g"'). Thus, the array element `data["12.153"]' is assigned the value one. The program then changes the value of `CONVFMT'. The test `(xyz in data)' generates a new string value from `xyz'--this time `"12.15"'--because the value of `CONVFMT' only allows two significant digits. This test fails, since `"12.15"' is a different string from `"12.153"'. According to the rules for conversions (*note Conversion::), integer values are always converted to strings as integers, no matter what the value of `CONVFMT' may happen to be. So the usual case of the following works: d7403 6 a7408 11 The "integer values always convert to strings as integers" rule has an additional consequence for array indexing. Octal and hexadecimal constants (*note Nondecimal-numbers::) are converted internally into numbers, and their original form is forgotten. This means, for example, that `array[17]', `array[021]', and `array[0x11]' all refer to the same element! As with many things in `awk', the majority of the time things work as one would expect them to. But it is useful to have a precise knowledge of the actual rules which sometimes can have a subtle effect on your programs. d7416 3 a7418 3 Suppose it's necessary to write a program to print the input data in reverse order. A reasonable attempt to do so (with some test data) might look like this: d7435 5 a7439 1 value zero. So, `awk' should have printed the value of `l[0]'. d7441 1 a7441 4 The issue here is that subscripts for `awk' arrays are _always_ strings. Uninitialized variables, when used as strings, have the value `""', not zero. Thus, `line 1' ends up stored in `l[""]'. The following version of the program works correctly: d7450 1 a7450 1 value" numeric zero. This is then converted to `"0"' as the array d7453 4 a7456 4 Even though it is somewhat unusual, the null string (`""') is a valid array subscript. (d.c.) `gawk' warns about the use of the null string as a subscript if `--lint' is provided on the command line (*note Options::). d7461 2 a7462 2 Multidimensional Arrays ======================= d7464 2 a7465 2 A multidimensional array is an array in which an element is identified by a sequence of indices instead of a single index. For d7470 4 a7473 3 Multidimensional arrays are supported in `awk' through concatenation of indices into one string. `awk' converts the indices into strings (*note Conversion::) and concatenates them together, with a separator d7480 1 a7480 1 when the value of `SUBSEP' is `"@@"'. The numbers 5 and 12 are d7490 14 a7503 12 a nonprinting character that is unlikely to appear in an `awk' program or in most input data. The usefulness of choosing an unlikely character comes from the fact that index values that contain a string matching `SUBSEP' can lead to combined strings that are ambiguous. Suppose that `SUBSEP' is `"@@"'; then `foo["a@@b", "c"]' and `foo["a", "b@@c"]' are indistinguishable because both are actually stored as `foo["a@@b@@c"]'. To test whether a particular index sequence exists in a multidimensional array, use the same operator (`in') that is used for single dimensional arrays. Write the whole sequence of indices in parentheses, separated by commas, as the left operand: d7509 1 a7509 1 result. It assumes that all lines have the same number of elements: d7511 1 a7511 1 { d7525 1 a7525 1 } d7534 1 a7534 1 the program produces the following output: d7544 1 a7544 1 File: gawk.info, Node: Multi-scanning, Next: Array Sorting, Prev: Multi-dimensional, Up: Arrays d7546 2 a7547 2 Scanning Multidimensional Arrays ================================ d7550 3 a7552 3 "multidimensional" array. There cannot be one, because, in truth, there are no multidimensional arrays or elements--there is only a multidimensional _way of accessing_ an array. d7555 5 a7559 4 multidimensional, you can get the effect of scanning it by combining the scanning `for' statement (*note Scanning an Array::) with the built-in `split' function (*note String Functions::). It works in the following manner: d7562 2 a7563 2 split(combined, separate, SUBSEP) ... d7566 11 a7576 11 This sets the variable `combined' to each concatenated combined index in the array, and splits it into the individual indices by breaking it apart where the value of `SUBSEP' appears. The individual indices then become the elements of the array `separate'. Thus, if a value is previously stored in `array[1, "foo"]'; then an element with index `"1\034foo"' exists in `array'. (Recall that the default value of `SUBSEP' is the character with code 034.) Sooner or later, the `for' statement finds that index and does an iteration with the variable `combined' set to `"1\034foo"'. Then the `split' function is called as follows: d7580 2 a7581 2 The result is to set `separate[1]' to `"1"' and `separate[2]' to `"foo"'. Presto! The original sequence of separate indices is d7585 1 a7585 106 File: gawk.info, Node: Array Sorting, Prev: Multi-scanning, Up: Arrays Sorting Array Values and Indices with `gawk' ============================================ The order in which an array is scanned with a `for (i in array)' loop is essentially arbitrary. In most `awk' implementations, sorting an array requires writing a `sort' function. While this can be educational for exploring different sorting algorithms, usually that's not the point of the program. `gawk' provides the built-in `asort' and `asorti' functions (*note String Functions::) for sorting arrays. For example: POPULATE THE ARRAY data n = asort(data) for (i = 1; i <= n; i++) DO SOMETHING WITH data[i] After the call to `asort', the array `data' is indexed from 1 to some number N, the total number of elements in `data'. (This count is `asort''s return value.) `data[1]' <= `data[2]' <= `data[3]', and so on. The comparison of array elements is done using `gawk''s usual comparison rules (*note Typing and Comparison::). An important side effect of calling `asort' is that _the array's original indices are irrevocably lost_. As this isn't always desirable, `asort' accepts a second argument: POPULATE THE ARRAY source n = asort(source, dest) for (i = 1; i <= n; i++) DO SOMETHING WITH dest[i] In this case, `gawk' copies the `source' array into the `dest' array and then sorts `dest', destroying its indices. However, the `source' array is not affected. Often, what's needed is to sort on the values of the _indices_ instead of the values of the elements. To do that, starting with `gawk' 3.1.2, use the `asorti' function. The interface is identical to that of `asort', except that the index values are used for sorting, and become the values of the result array: { source[$0] = some_func($0) } END { n = asorti(source, dest) for (i = 1; i <= n; i++) DO SOMETHING WITH dest[i] } If your version of `gawk' is 3.1.0 or 3.1.1, you don't have `asorti'. Instead, use a helper array to hold the sorted index values, and then access the original array's elements. It works in the following way: POPULATE THE ARRAY data # copy indices j = 1 for (i in data) { ind[j] = i # index value becomes element value j++ } n = asort(ind) # index values are now sorted for (i = 1; i <= n; i++) DO SOMETHING WITH data[ind[i]] Sorting the array by replacing the indices provides maximal flexibility. To traverse the elements in decreasing order, use a loop that goes from N down to 1, either over the elements or over the indices. Copying array indices and elements isn't expensive in terms of memory. Internally, `gawk' maintains "reference counts" to data. For example, when `asort' copies the first array to the second one, there is only one copy of the original array elements' data, even though both arrays use the values. Similarly, when copying the indices from `data' to `ind', there is only one copy of the actual index strings. We said previously that comparisons are done using `gawk''s "usual comparison rules." Because `IGNORECASE' affects string comparisons, the value of `IGNORECASE' also affects sorting for both `asort' and `asorti'. Caveat Emptor.  File: gawk.info, Node: Functions, Next: Internationalization, Prev: Arrays, Up: Top Functions ********* This major node describes `awk''s built-in functions, which fall into three categories: numeric, string, and I/O. `gawk' provides additional groups of functions to work with values that represent time, do bit manipulation, and internationalize and localize programs. Besides the built-in functions, `awk' has provisions for writing new functions that the rest of a program can use. The second half of this major node describes these "user-defined" functions. * Menu: * Built-in:: Summarizes the built-in functions. * User-defined:: Describes User-defined functions in detail.  File: gawk.info, Node: Built-in, Next: User-defined, Up: Functions d7588 1 a7588 1 ================== d7590 5 a7594 4 "Built-in" functions are always available for your `awk' program to call. This minor node defines all the built-in functions in `awk'; some of these are mentioned in other sections but are summarized here for your convenience. d7602 2 a7603 1 `split', `match' and `sprintf'. d7605 1 a7605 3 * Time Functions:: Functions for dealing with timestamps. * Bitwise Functions:: Functions for bitwise operations. * I18N Functions:: Functions for string translation. d7608 1 a7608 1 File: gawk.info, Node: Calling Built-in, Next: Numeric Functions, Up: Built-in d7611 1 a7611 1 -------------------------- d7613 3 a7615 3 To call one of `awk''s built-in functions, write the name of the function followed by arguments in parentheses. For example, `atan2(y + z, 1)' is a call to the function `atan2' and has two arguments. d7618 1 a7618 1 open parenthesis, and it is good practice to avoid using whitespace d7620 2 a7621 2 it is easier to avoid mistakes by following a simple convention that always works--no whitespace after a function name. d7631 2 a7632 2 actual parameters are evaluated completely before the call is performed. For example, in the following code fragment: d7637 7 a7643 5 the variable `i' is incremented to the value five before `sqrt' is called with a value of four for its actual parameter. The order of evaluation of the expressions used for the function's parameters is undefined. Thus, avoid writing programs that assume that parameters are evaluated from left to right or from right to left. For example: d7649 3 a7651 3 6, and then 12, and `atan2' is called with the two arguments 6 and 12. But if the order of evaluation is right to left, `i' first becomes 10, then 11, and `atan2' is called with the two arguments 11 and 10. d7656 2 a7657 2 Numeric Functions ----------------- d7659 2 a7660 3 The following list describes all of the built-in functions that work with numbers. Optional parameters are enclosed in square brackets ([ ]): d7663 2 a7664 2 This returns the nearest integer to X, located between X and zero and truncated toward zero. d7666 2 a7667 2 For example, `int(3)' is 3, `int(3.9)' is 3, `int(-3.9)' is -3, and `int(-3)' is -3 as well. d7670 2 a7671 2 This returns the positive square root of X. `gawk' reports an error if X is negative. Thus, `sqrt(4)' is 2. d7674 3 a7676 3 This returns the exponential of X (`e ^ X') or reports an error if X is out of range. The range of values X can have depends on your machine's floating-point representation. d7679 1 a7679 1 This returns the natural logarithm of X, if X is positive; d7683 1 a7683 1 This returns the sine of X, with X in radians. d7686 1 a7686 1 This returns the cosine of X, with X in radians. d7689 1 a7689 1 This returns the arctangent of `Y / X' in radians. d7692 7 a7698 7 This returns a random number. The values of `rand' are uniformly distributed between zero and one. The value could be zero but is never one.(1) Often random integers are needed instead. Following is a user-defined function that can be used to obtain a random non-negative integer less than N: d7704 2 a7705 2 The multiplication produces a random number greater than zero and less than `n'. Using `int', this result is made into an integer d7708 3 a7710 3 The following example uses a similar function to produce random integers between one and N. This program prints a new random number for each input record: d7712 1 d7721 1 a7721 1 } d7725 7 a7731 6 "seed", each time you run `awk'. Thus, a program generates the same results each time you run it. The numbers are random within one `awk' run but predictable from run to run. This is convenient for debugging, but if you want a program to do different things each time it is used, you must change the seed to a value that is different in each run. To do this, use `srand'. d7738 2 a7739 2 numbers.(2) Thus, if the seed is set to the same value a second time, the same sequence of random numbers is produced again. d7741 3 a7743 8 Different `awk' implementations use different random-number generators internally. Don't expect the same `awk' program to produce the same series of random numbers when executed by different versions of `awk'. If the argument X is omitted, as in `srand()', then the current date and time of day are used for a seed. This is the way to get random numbers that are truly unpredictable. d7746 2 a7747 2 easy to keep track of the seeds in case you need to consistently reproduce sequences of random numbers. d7751 2 a7752 8 (1) The C version of `rand' is known to produce fairly poor sequences of random numbers. However, nothing requires that an `awk' implementation use the C `rand' to implement the `awk' version of `rand'. In fact, `gawk' uses the BSD `random' function, which is considerably better than `rand', to produce random numbers. (2) Computer-generated random numbers really are not truly random. They are technically known as "pseudorandom." This means that while d7759 2 a7760 38 String-Manipulation Functions ----------------------------- The functions in this minor node look at or change the text of one or more strings. Optional parameters are enclosed in square brackets ([ ]). Those functions that are specific to `gawk' are marked with a pound sign (`#'): * Menu: * Gory Details:: More than you want to know about `\' and `&' with `sub', `gsub', and `gensub'. `asort(SOURCE [, DEST]) #' `asort' is a `gawk'-specific extension, returning the number of elements in the array SOURCE. The contents of SOURCE are sorted using `gawk''s normal rules for comparing values (in particular, `IGNORECASE' affects the sorting) and the indices of the sorted values of SOURCE are replaced with sequential integers starting with one. If the optional array DEST is specified, then SOURCE is duplicated into DEST. DEST is then sorted, leaving the indices of SOURCE unchanged. For example, if the contents of `a' are as follows: a["last"] = "de" a["first"] = "sac" a["middle"] = "cul" A call to `asort': asort(a) results in the following contents of `a': a[1] = "cul" a[2] = "de" a[3] = "sac" d7762 3 a7764 16 The `asort' function is described in more detail in *Note Array Sorting::. `asort' is a `gawk' extension; it is not available in compatibility mode (*note Options::). `asorti(SOURCE [, DEST]) #' `asorti' is a `gawk'-specific extension, returning the number of elements in the array SOURCE. It works similarly to `asort', however, the _indices_ are sorted, instead of the values. As array indices are always strings, the comparison performed is always a string comparison. (Here too, `IGNORECASE' affects the sorting.) The `asorti' function is described in more detail in *Note Array Sorting::. It was added in `gawk' 3.1.2. `asorti' is a `gawk' extension; it is not available in compatibility mode (*note Options::). d7769 1 a7769 1 begins in the string IN. Consider the following example: d7778 1 a7778 1 This returns the number of characters in STRING. If STRING is a d7780 2 a7781 2 returned. For example, `length("abcde")' is 5. By contrast, `length(15 * 35)' works out to 3. In this example, 15 * 35 = 525, d7787 14 a7800 24 *Note:* In older versions of `awk', the `length' function could be called without any parentheses. Doing so is marked as "deprecated" in the POSIX standard. This means that while a program can do this, it is a feature that can eventually be removed from a future version of the standard. Therefore, for programs to be maximally portable, always supply the parentheses. `match(STRING, REGEXP [, ARRAY])' The `match' function searches STRING for the longest, leftmost substring matched by the regular expression, REGEXP. It returns the character position, or "index", at which that substring begins (one, if it starts at the beginning of STRING). If no match is found, it returns zero. The REGEXP argument may be either a regexp constant (`/.../') or a string constant ("..."). In the latter case, the string is treated as a regexp to be matched. *Note Computed Regexps::, for a discussion of the difference between the two forms, and the implications for writing your program correctly. The order of the first two arguments is backwards from most other string functions that work with regular expressions, such as `sub' and `gsub'. It might help to remember that for `match', the order is the same as for the `~' operator: `STRING ~ REGEXP'. d7809 1 a7809 1 { d7815 1 a7815 1 print "Match of", regex, "found at", d7818 1 a7818 1 } d7823 1 a7823 1 changed to be the second word on that line. Therefore, if given: a7837 34 If ARRAY is present, it is cleared, and then the 0th element of ARRAY is set to the entire portion of STRING matched by REGEXP. If REGEXP contains parentheses, the integer-indexed elements of ARRAY are set to contain the portion of STRING matching the corresponding parenthesized subexpression. For example: $ echo foooobazbarrrrr | > gawk '{ match($0, /(fo+).+(bar*)/, arr) > print arr[1], arr[2] }' -| foooo barrrrr In addition, beginning with `gawk' 3.1.2, multidimensional subscripts are available providing the start index and length of each matched subexpression: $ echo foooobazbarrrrr | > gawk '{ match($0, /(fo+).+(bar*)/, arr) > print arr[1], arr[2] > print arr[1, "start"], arr[1, "length"] > print arr[2, "start"], arr[2, "length"] > }' -| foooo barrrrr -| 1 5 -| 9 7 There may not be subscripts for the start and index for every parenthesized subexpressions, since they may not all have matched text; thus they should be tested for with the `in' operator (*note Reference to Elements::). The ARRAY argument to `match' is a `gawk' extension. In compatibility mode (*note Options::), using a third argument is a fatal error. d7839 7 a7845 8 This function divides STRING into pieces separated by FIELDSEP and stores the pieces in ARRAY. The first piece is stored in `ARRAY[1]', the second piece in `ARRAY[2]', and so forth. The string value of the third argument, FIELDSEP, is a regexp describing where to split STRING (much as `FS' can be a regexp describing where to split input records). If FIELDSEP is omitted, the value of `FS' is used. `split' returns the number of elements created. d7863 9 a7871 15 are separated by runs of whitespace. Also as with input field-splitting, if FIELDSEP is the null string, each individual character in the string is split into its own array element. (This is a `gawk'-specific extension.) Note, however, that `RS' has no effect on the way `split' works. Even though `RS = ""' causes newline to also be an input field separator, this does not affect how `split' splits strings. Modern implementations of `awk', including `gawk', allow the third argument to be a regexp constant (`/abc/') as well as a string. (d.c.) The POSIX standard allows this as well. *Note Computed Regexps::, for a discussion of the difference between using a string constant or a regexp constant, and the implications for writing your program correctly. d7874 1 a7874 9 existing elements in the array ARRAY. If STRING is null, the array has no elements. (So this is a portable way to delete an entire array with one statement. *Note Delete::.) If STRING does not match FIELDSEP at all (but is not null), ARRAY has one element only. The value of that element is the original STRING. d7876 1 a7876 1 `sprintf(FORMAT, EXPRESSION1, ...)' d7878 2 a7879 4 have printed out with the same arguments (*note Printf::). For example: pival = sprintf("pi = %.2f (approx.)", 22/7) d7881 1 a7881 1 assigns the string `"pi = 3.14 (approx.)"' to the variable `pival'. d7883 1 a7883 16 `strtonum(STR) #' Examines STR and returns its numeric value. If STR begins with a leading `0', `strtonum' assumes that STR is an octal number. If STR begins with a leading `0x' or `0X', `strtonum' assumes that STR is a hexadecimal number. For example: $ echo 0x11 | > gawk '{ printf "%d\n", strtonum($1) }' -| 17 Using the `strtonum' function is _not_ the same as adding zero to a string value; the automatic coercion of strings to numbers works only for decimal data, not for octal or hexadecimal.(1) `strtonum' is a `gawk' extension; it is not available in compatibility mode (*note Options::). d7887 5 a7891 10 value, which is treated as a string, for the leftmost, longest substring matched by the regular expression REGEXP. Then the entire string is changed by replacing the matched text with REPLACEMENT. The modified string becomes the new value of TARGET. The REGEXP argument may be either a regexp constant (`/.../') or a string constant ("..."). In the latter case, the string is treated as a regexp to be matched. *Note Computed Regexps::, for a discussion of the difference between the two forms, and the implications for writing your program correctly. d7894 2 a7895 2 compute a value, and not just any expression will do--it must be a variable, field, or array element so that `sub' can store a d7897 3 a7899 1 default is to use and alter `$0'.(2) For example: d7905 1 a7905 1 leftmost longest occurrence of `at' with `ith'. d7915 1 a7915 1 { sub(/candidate/, "& and his wife"); print } d7918 3 a7920 1 wife' on each input line. Here is another example: d7922 6 a7927 6 $ awk 'BEGIN { > str = "daabaaa" > sub(/a+/, "C&C", str) > print str > }' -| dCaaCbaaa d7929 1 a7929 1 This shows how `&' can represent a nonconstant string and also d7931 1 a7931 1 Leftmost Longest::). d7937 2 a7938 2 `&' in the replacement. For example, the following shows how to replace the first `|' on each line with an `&': d7940 1 a7940 1 { sub(/\|/, "\\&"); print } d7942 7 a7948 7 As mentioned, the third argument to `sub' must be a variable, field or array reference. Some versions of `awk' allow the third argument to be an expression that is not an lvalue. In such a case, `sub' still searches for the pattern and returns zero or one, but the result of the substitution (if any) is thrown away because there is no place to put it. Such versions of `awk' accept expressions such as the following: d7952 4 a7955 8 For historical compatibility, `gawk' accepts erroneous code, such as in the previous example. However, using any other nonchangeable object as the third parameter causes a fatal error and your program will not run. Finally, if the REGEXP is not a regexp constant, it is converted into a string, and then the value of that string is treated as the regexp to match. d7959 1 a7959 1 _all_ of the longest, leftmost, _nonoverlapping_ matching d7963 1 a7963 1 { gsub(/Britain/, "United Kingdom"); print } d7969 2 a7970 3 the variable to search and alter (TARGET) is omitted, then the entire input record (`$0') is used. As in `sub', the characters `&' and `\' are special, and the third argument must be assignable. d7972 4 a7975 1 `gensub(REGEXP, REPLACEMENT, HOW [, TARGET]) #' d7979 2 a7980 2 string is returned as the result of the function and the original target string is _not_ changed. If HOW is a string beginning with d7982 2 a7983 3 REPLACEMENT. Otherwise, HOW is treated as a number that indicates which match of REGEXP to replace. If no TARGET is supplied, `$0' is used. d7988 3 a7990 2 regexp to mark the components and then specifying `\N' in the replacement text, where N is a digit from 1 to 9. For example: d8000 2 a8001 3 As with `sub', you must type two backslashes in order to get one into the string. In the replacement text, the sequence `\0' represents the entire matched text, as does the character `&'. d8003 5 a8007 2 The following example shows how you can use the third argument to control which match of the regexp should be changed: d8018 2 a8019 6 `G', or if it is a number that is less than or equal to zero, only one substitution is performed. If HOW is zero, `gawk' issues a warning message. If REGEXP does not match TARGET, `gensub''s return value is the original unchanged value of TARGET. d8022 1 a8022 1 compatibility mode (*note Options::). d8027 1 a8027 1 character number one.(3) For example, `substr("washington", 5, 3)' d8034 1 a8034 1 remaining in the string, counting from character START. d8036 3 a8038 10 If START is less than one, `substr' treats it as if it was one. (POSIX doesn't specify what to do in this case: Unix `awk' acts this way, and therefore `gawk' does too.) If START is greater than the number of characters in the string, `substr' returns the null string. Similarly, if LENGTH is present but less than or equal to zero, the null string is returned. The string returned by `substr' _cannot_ be assigned. Thus, it is a mistake to attempt to change a portion of a string, as shown in the following example: d8044 1 a8044 2 It is also a mistake to use `substr' as the third argument of `sub' or `gsub': a8047 10 (Some commercial versions of `awk' do in fact let you use `substr' this way, but doing so is not portable.) If you need to replace bits and pieces of a string, combine `substr' with string concatenation, in the following manner: string = "abcdef" ... string = substr(string, 1, 2) "CDE" substr(string, 6) d8049 3 a8051 3 This returns a copy of STRING, with each uppercase character in the string replaced with its corresponding lowercase character. Nonalphabetic characters are left unchanged. For example, d8055 3 a8057 3 This returns a copy of STRING, with each lowercase character in the string replaced with its corresponding uppercase character. Nonalphabetic characters are left unchanged. For example, d8060 2 a8061 18 ---------- Footnotes ---------- (1) Unless you use the `--non-decimal-data' option, which isn't recommended. *Note Nondecimal Data::, for more information. (2) Note that this means that the record will first be regenerated using the value of `OFS' if any fields have been changed, and that the fields will be updated after the substituion, even if the operation is a "no-op" such as `sub(/^/, "")'. (3) This is different from C and C++, in which the first character is number zero.  File: gawk.info, Node: Gory Details, Up: String Functions More About `\' and `&' with `sub', `gsub', and `gensub' ....................................................... d8063 1 a8063 1 When using `sub', `gsub', or `gensub', and trying to get literal d8068 4 a8071 2 program and builds an internal copy of it that can be executed. Then there is the runtime level, which is when `awk' actually scans the d8077 1 a8077 1 `awk' processes at the runtime level, type two backslashes at the d8080 1 a8080 1 initial `\' and put the next character into the string. Thus, for d8083 1 a8083 1 At the runtime level, the various functions handle sequences of `\' d8085 5 a8089 4 Historically, the `sub' and `gsub' functions treated the two character sequence `\&' specially; this sequence was replaced in the generated text with a single `&'. Any other `\' within the REPLACEMENT string that did not precede an `&' was passed through unchanged. To d8102 5 a8106 5 This table shows both the lexical-level processing, where an odd number of backslashes becomes an even number at the runtime level, as well as the runtime processing done by `sub'. (For the sake of simplicity, the rest of the following tables only show the case of even numbers of backslashes entered at the lexical level.) d8114 1 a8114 1 The interpretation of `\' and `&' then becomes: d8123 5 a8127 5 This appears to solve the problem. Unfortunately, the phrasing of the standard is unusual. It says, in effect, that `\' turns off the special meaning of any following character, but for anything other than `\' and `&', such special meaning is undefined. This wording leads to two problems: d8129 1 a8129 1 * Backslashes must now be doubled in the REPLACEMENT string, breaking d8132 1 a8132 1 * To make sure that an `awk' program is portable, _every_ character d8135 2 a8136 2 The POSIX standard is under revision. Because of the problems just listed, proposed text for the revised standard reverts to rules that d8139 1 a8139 1 preceding the matched text: d8148 2 a8149 2 In a nutshell, at the runtime level, there are now three special sequences of characters (`\\\&', `\\&' and `\&') whereas historically d8151 1 a8151 1 is not part of one of these three sequences is not special and appears d8154 5 a8158 5 `gawk' 3.0 and 3.1 follow these proposed POSIX rules for `sub' and `gsub'. Whether these proposed rules will actually become codified into the standard is unknown at this point. Subsequent `gawk' releases will track the standard and implement whatever the final version specifies; this Info file will be updated as well.(2) d8160 1 a8160 1 The rules for `gensub' are considerably simpler. At the runtime d8164 2 a8165 2 what character follows the `\', it appears in the generated text and the `\' does not: d8176 3 a8178 15 Because of the complexity of the lexical and runtime level processing and the special cases for `sub' and `gsub', we recommend the use of `gawk' and `gensub' when you have to do substitutions. Advanced Notes: Matching the Null String ---------------------------------------- In `awk', the `*' operator can match the null string. This is particularly important for the `sub', `gsub', and `gensub' functions. For example: $ echo abc | awk '{ gsub(/m*/, "X"); print }' -| XaXbXcX Although this makes a certain amount of sense, it can be surprising. d8182 1 a8182 1 (1) This consequence was certainly unintended. d8184 2 a8185 3 (2) As this Info file was being finalized, we learned that the POSIX standard will not use these rules. However, it was too late to change `gawk' for the 3.1 release. `gawk' behaves as described here. d8190 2 a8191 2 Input/Output Functions ---------------------- d8193 2 a8194 2 The following functions relate to input/output (I/O). Optional parameters are enclosed in square brackets ([ ]): d8196 6 a8201 14 `close(FILENAME [, HOW])' Close the file FILENAME for input or output. Alternatively, the argument may be a shell command that was used for creating a coprocess, or for redirecting to or from a pipe; then the coprocess or pipe is closed. *Note Close Files And Pipes::, for more information. When closing a coprocess, it is occasionally useful to first close one end of the two-way pipe and then to close the other. This is done by providing a second argument to `close'. This second argument should be one of the two string values `"to"' or `"from"', indicating which end of the pipe to close. Case in the string does not matter. *Note Two-way I/O::, which discusses this feature in more detail and gives an example. d8204 8 a8211 8 Flush any buffered output associated with FILENAME, which is either a file opened for writing or a shell command for redirecting output to a pipe or coprocess. Many utility programs "buffer" their output; i.e., they save information to write to a disk file or terminal in memory until there is enough for it to be worthwhile to send the data to the output device. This is often more efficient than writing every d8216 2 a8217 2 function--`gawk' also buffers its output and the `fflush' function forces `gawk' to flush its buffers. d8219 4 a8222 4 `fflush' was added to the Bell Laboratories research version of `awk' in 1994; it is not part of the POSIX standard and is not available if `--posix' has been specified on the command line (*note Options::). d8226 6 a8231 14 standard output is flushed. The second is to allow the null string (`""') as the argument. In this case, the buffers for _all_ open output files and pipes are flushed. `fflush' returns zero if the buffer is successfully flushed; otherwise, it returns -1. In the case where all buffers are flushed, the return value is zero only if all buffers were flushed successfully. Otherwise, it is -1, and `gawk' warns about the problem FILENAME. `gawk' also issues a warning message if you attempt to flush a file or pipe that was opened for reading (such as with `getline'), or if FILENAME is not an open file, pipe, or coprocess. In such a case, `fflush' returns -1, as well. d8234 5 a8238 4 Executes operating-system commands and then returns to the `awk' program. The `system' function executes the command given by the string COMMAND. It returns the status returned by the command that was executed as its value. d8247 1 a8247 1 the system administrator is sent mail when the `awk' program d8251 6 a8256 12 enough to accomplish your task. If you need to run many commands, it is more efficient to simply print them down a pipeline to the shell: while (MORE STUFF TO DO) print COMMAND | "/bin/sh" close("/bin/sh") However, if your `awk' program is interactive, `system' is useful for cranking up large self-contained programs, such as a shell or an editor. Some operating systems cannot implement the `system' function. `system' causes a fatal error if it is not supported. d8258 2 a8259 2 Advanced Notes: Interactive Versus Noninteractive Buffering ----------------------------------------------------------- d8261 2 a8262 2 As a side point, buffering issues can be even more confusing, depending upon whether your program is "interactive", i.e., d8265 5 a8269 4 Interactive programs generally "line buffer" their output; i.e., they write out every line. Noninteractive programs wait until they have a full buffer, which may be many lines of output. Here is an example of the difference: d8276 1 a8276 1 Ctrl-d d8279 1 a8279 1 this example: d8284 1 a8284 1 Ctrl-d d8288 2 a8289 2 Here, no output is printed until after the `Ctrl-d' is typed, because it is all buffered and sent down the pipe to `cat' in one shot. d8291 2 a8292 2 Advanced Notes: Controlling Output Buffering with `system' ---------------------------------------------------------- d8297 1 a8297 1 flush output buffers is to call `system' with a null string as its d8302 1 a8302 1 `gawk' treats this use of the `system' function as a special case and d8305 2 a8306 2 useful, it is also efficient. While this method should work with other `awk' implementations, it does not necessarily avoid starting an d8308 1 a8308 1 associated with the standard output and not necessarily all buffered d8320 1 a8320 1 must print: d8326 1 a8326 1 and not: d8332 2 a8333 2 If `awk' did not flush its buffers before calling `system', you would see the latter (undesirable) output. d8337 1 a8337 1 (1) A program is interactive if the standard output is connected to d8341 1 a8341 1 File: gawk.info, Node: Time Functions, Next: Bitwise Functions, Prev: I/O Functions, Up: Built-in d8343 14 a8356 2 Using `gawk''s Timestamp Functions ---------------------------------- d8358 1 a8358 16 `awk' programs are commonly used to process log files containing timestamp information, indicating when a particular log record was written. Many programs log their timestamp in the form returned by the `time' system call, which is the number of seconds since a particular epoch. On POSIX-compliant systems, it is the number of seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds.(1) All known POSIX-compliant systems support timestamps from 0 through 2^31 - 1, which is sufficient to represent times through 2038-01-19 03:14:07 UTC. Many systems support a wider range of timestamps, including negative timestamps that represent times before the epoch. In order to make it easier to process such log files and to produce useful reports, `gawk' provides the following functions for working with timestamps. They are `gawk' extensions; they are not specified in the POSIX standard, nor are they in any other known version of `awk'.(2) Optional parameters are enclosed in square brackets ([ ]): d8363 2 a8364 25 seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds. It may be a different number on other systems. `mktime(DATESPEC)' This function turns DATESPEC into a timestamp in the same form as is returned by `systime'. It is similar to the function of the same name in ISO C. The argument, DATESPEC, is a string of the form `"YYYY MM DD HH MM SS [DST]"'. The string consists of six or seven numbers representing, respectively, the full year including century, the month from 1 to 12, the day of the month from 1 to 31, the hour of the day from 0 to 23, the minute from 0 to 59, the second from 0 to 60,(3) and an optional daylight-savings flag. The values of these numbers need not be within the ranges specified; for example, an hour of -1 means 1 hour before midnight. The origin-zero Gregorian calendar is assumed, with year 0 preceding year 1 and year -1 preceding year 0. The time is assumed to be in the local timezone. If the daylight-savings flag is positive, the time is assumed to be daylight savings time; if zero, the time is assumed to be standard time; and if negative (the default), `mktime' attempts to determine whether daylight savings time is in effect for the specified time. If DATESPEC does not contain enough elements or if the resulting time is out of range, `mktime' returns -1. d8368 3 a8370 3 the same name in ISO C. The time specified by TIMESTAMP is used to produce a string, based on the contents of the FORMAT string. The TIMESTAMP is in the same format as the value returned by the d8372 1 a8372 1 uses the current time of day as the timestamp. If no FORMAT d8374 3 a8376 3 This format string produces output that is (almost) equivalent to that of the `date' utility. (Versions of `gawk' prior to 3.0 require the FORMAT argument.) d8378 1 a8378 1 The `systime' function allows you to compare a timestamp from a log d8383 1 a8383 7 The `mktime' function allows you to convert a textual representation of a date and time into a timestamp. This makes it easy to do before/after comparisons of dates and times, particularly when dealing with date and time data coming from an external source, such as a log file. The `strftime' function allows you to easily turn a timestamp into d8385 4 a8388 4 function (*note String Functions::), in that it copies nonformat specification characters verbatim to the returned string, while substituting date and time values for format specifications in the FORMAT string. d8390 2 a8391 2 `strftime' is guaranteed by the 1999 ISO C standard(4) to support the following date format specifications: d8406 1 a8406 6 The locale's "appropriate" date and time representation. (This is `%A %B %d %T %Y' in the `"C"' locale.) `%C' The century. This is the year divided by 100 and truncated to the next lower integer. a8410 24 `%D' Equivalent to specifying `%m/%d/%y'. `%e' The day of the month, padded with a space if it is only one digit. `%F' Equivalent to specifying `%Y-%m-%d'. This is the ISO 8601 date format. `%g' The year modulo 100 of the ISO week number, as a decimal number (00-99). For example, January 1, 1993 is in week 53 of 1992. Thus, the year of its ISO week number is 1992, even though its year is 1993. Similarly, December 31, 1973 is in week 1 of 1974. Thus, the year of its ISO week number is 1974, even though its year is 1973. `%G' The full year of the ISO week number, as a decimal number. `%h' Equivalent to `%b'. a8425 3 `%n' A newline character (ASCII LF). a8429 7 `%r' The locale's 12-hour clock time. (This is `%I:%M:%S %p' in the `"C"' locale.) `%R' Equivalent to specifying `%H:%M'. d8431 1 a8431 10 The second as a decimal number (00-60). `%t' A TAB character. `%T' Equivalent to specifying `%H:%M:%S'. `%u' The weekday as a decimal number (1-7). Monday is day one. a8436 8 `%V' The week number of the year (the first Monday as the first day of week one) as a decimal number (01-53). The method for determining the week number is as specified by ISO 8601. (To wit: if the week containing January 1 has four or more days in the new year, then it is week one; otherwise it is week 53 of the previous year and the next week is week one.) d8445 1 a8445 2 The locale's "appropriate" date representation. (This is `%A %B %d %Y' in the `"C"' locale.) d8448 1 a8448 2 The locale's "appropriate" time representation. (This is `%T' in the `"C"' locale.) d8451 1 a8451 1 The year modulo 100 as a decimal number (00-99). d8454 1 a8454 5 The full year as a decimal number (e.g., 1995). `%z' The timezone offset in a +HHMM format (e.g., the format necessary to produce RFC 822/RFC 1036 date headers). d8457 2 a8458 8 The time zone name or abbreviation; no characters if no time zone is determinable. `%Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH' `%OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy' "Alternate representations" for the specifications that use only the second letter (`%c', `%C', and so on).(5) (These facilitate compliance with the POSIX `date' utility.) d8464 1 a8464 1 undefined.(6) d8468 4 a8471 4 September 4, 1991 in the United States is "9/4/91." In many countries in Europe, however, it is abbreviated "4.9.91." Thus, the `%x' specification in a `"US"' locale might produce `9/4/91', while in a `"EUROPE"' locale, it might produce `4.9.91'. The ISO C standard d8476 27 a8502 4 systems that are not yet fully standards-compliant. It supports all of the just listed format specifications. If that version is used to compile `gawk' (*note Installation::), then the following additional format specifications are available: d8505 1 a8505 1 The hour (24-hour clock) as a decimal number (0-23). Single-digit d8509 1 a8509 1 The hour (12-hour clock) as a decimal number (1-12). Single-digit d8512 21 a8532 2 `%N' The "Emperor/Era" name. Equivalent to `%C'. d8534 3 a8536 2 `%o' The "Emperor/Era" year. Equivalent to `%y'. d8538 6 a8543 2 `%s' The time as a decimal timestamp in seconds since the epoch. d8546 1 a8546 1 The date in VMS format (e.g., `20-JUN-1991'). d8548 3 a8550 2 Additionally, the alternate representations are recognized but their normal representations are used. d8554 4 a8557 4 in a well-known format. However, if you provide an argument to it that begins with a `+', `date' copies nonformat specifier characters to the standard output and interprets the current time according to the format specifiers in the string. For example: d8560 1 a8560 1 -| Today is Thursday, September 14, 2000. d8563 2 a8564 2 "wrapper" to handle the `-u' option, which requires that `date' run as if the time zone is set to UTC: d8571 1 a8571 1 -u) TZ=UTC0 # use UTC d8593 1 a8593 7 (1) *Note Glossary::, especially the entries "Epoch" and "UTC." (2) The GNU `date' utility can also do many of the things described here. Its use may be preferable for simple time-related operations in shell scripts. (3) Occasionally there are minutes in a year with a leap second, d8596 4 a8599 136 (4) As this is a recent standard, not every system's `strftime' necessarily supports all of the conversions listed here. (5) If you don't understand any of this, don't worry about it; these facilities are meant to make it easier to "internationalize" programs. Other internationalization features are described in *Note Internationalization::. (6) This is because ISO C leaves the behavior of the C version of `strftime' undefined and `gawk' uses the system's version of `strftime' if it's there. Typically, the conversion specifier either does not appear in the returned string or appears literally.  File: gawk.info, Node: Bitwise Functions, Next: I18N Functions, Prev: Time Functions, Up: Built-in Bit-Manipulation Functions of `gawk' ------------------------------------ I can explain it for you, but I can't understand it for you. Anonymous Many languages provide the ability to perform "bitwise" operations on two integer numbers. In other words, the operation is performed on each successive pair of bits in the operands. Three common operations are bitwise AND, OR, and XOR. The operations are described by the following table: Bit Operator | AND | OR | XOR |---+---+---+---+---+--- Operands | 0 | 1 | 0 | 1 | 0 | 1 ----------+---+---+---+---+---+--- 0 | 0 0 | 0 1 | 0 1 1 | 0 1 | 1 1 | 1 0 As you can see, the result of an AND operation is 1 only when _both_ bits are 1. The result of an OR operation is 1 if _either_ bit is 1. The result of an XOR operation is 1 if either bit is 1, but not both. The next operation is the "complement"; the complement of 1 is 0 and the complement of 0 is 1. Thus, this operation "flips" all the bits of a given value. Finally, two other common operations are to shift the bits left or right. For example, if you have a bit string `10111001' and you shift it right by three bits, you end up with `00010111'.(1) If you start over again with `10111001' and shift it left by three bits, you end up with `11001000'. `gawk' provides built-in functions that implement the bitwise operations just described. They are: `and(V1, V2)' Returns the bitwise AND of the values provided by V1 and V2. `or(V1, V2)' Returns the bitwise OR of the values provided by V1 and V2. `xor(V1, V2)' Returns the bitwise XOR of the values provided by V1 and V2. `compl(VAL)' Returns the bitwise complement of VAL. `lshift(VAL, COUNT)' Returns the value of VAL, shifted left by COUNT bits. `rshift(VAL, COUNT)' Returns the value of VAL, shifted right by COUNT bits. For all of these functions, first the double-precision floating-point value is converted to the widest C unsigned integer type, then the bitwise operation is performed and then the result is converted back into a C `double'. (If you don't understand this paragraph, don't worry about it.) Here is a user-defined function (*note User-defined::) that illustrates the use of these functions: # bits2str --- turn a byte into readable 1's and 0's function bits2str(bits, data, mask) { if (bits == 0) return "0" mask = 1 for (; bits != 0; bits = rshift(bits, 1)) data = (and(bits, mask) ? "1" : "0") data while ((length(data) % 8) != 0) data = "0" data return data } BEGIN { printf "123 = %s\n", bits2str(123) printf "0123 = %s\n", bits2str(0123) printf "0x99 = %s\n", bits2str(0x99) comp = compl(0x99) printf "compl(0x99) = %#x = %s\n", comp, bits2str(comp) shift = lshift(0x99, 2) printf "lshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift) shift = rshift(0x99, 2) printf "rshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift) } This program produces the following output when run: $ gawk -f testbits.awk -| 123 = 01111011 -| 0123 = 01010011 -| 0x99 = 10011001 -| compl(0x99) = 0xffffff66 = 11111111111111111111111101100110 -| lshift(0x99, 2) = 0x264 = 0000001001100100 -| rshift(0x99, 2) = 0x26 = 00100110 The `bits2str' function turns a binary number into a string. The number `1' represents a binary value where the rightmost bit is set to 1. Using this mask, the function repeatedly checks the rightmost bit. ANDing the mask with the value indicates whether the rightmost bit is 1 or not. If so, a `"1"' is concatenated onto the front of the string. Otherwise, a `"0"' is added. The value is then shifted right by one bit and the loop continues until there are no more 1 bits. If the initial value is zero it returns a simple `"0"'. Otherwise, at the end, it pads the value with zeros to represent multiples of 8-bit quantities. This is typical in modern computers. The main code in the `BEGIN' rule shows the difference between the decimal and octal values for the same numbers (*note Nondecimal-numbers::), and then demonstrates the results of the `compl', `lshift', and `rshift' functions. ---------- Footnotes ---------- (1) This example shows that 0's come in on the left side. For `gawk', this is always true, but in some languages, it's possible to have the left side fill with 1's. Caveat emptor.  File: gawk.info, Node: I18N Functions, Prev: Bitwise Functions, Up: Built-in Using `gawk''s String-Translation Functions ------------------------------------------- d8601 3 a8603 29 `gawk' provides facilities for internationalizing `awk' programs. These include the functions described in the following list. The descriptions here are purposely brief. *Note Internationalization::, for the full story. Optional parameters are enclosed in square brackets ([ ]): `dcgettext(STRING [, DOMAIN [, CATEGORY]])' This function returns the translation of STRING in text domain DOMAIN for locale category CATEGORY. The default value for DOMAIN is the current value of `TEXTDOMAIN'. The default value for CATEGORY is `"LC_MESSAGES"'. `dcngettext(STRING1, STRING2, NUMBER [, DOMAIN [, CATEGORY]])' This function returns the plural form used for NUMBER of the translation of STRING1 and STRING2 in text domain DOMAIN for locale category CATEGORY. STRING1 is the English singular variant of a message, and STRING2 the English plural variant of the same message. The default value for DOMAIN is the current value of `TEXTDOMAIN'. The default value for CATEGORY is `"LC_MESSAGES"'. `bindtextdomain(DIRECTORY [, DOMAIN])' This function allows you to specify the directory in which `gawk' will look for message translation files, in case they will not or cannot be placed in the "standard" locations (e.g., during testing). It returns the directory in which DOMAIN is "bound." The default DOMAIN is the value of `TEXTDOMAIN'. If DIRECTORY is the null string (`""'), then `bindtextdomain' returns the current binding for the given DOMAIN. d8606 1 a8606 1 File: gawk.info, Node: User-defined, Prev: Built-in, Up: Functions d8608 2 a8609 2 User-Defined Functions ====================== d8613 2 a8614 2 ones (*note Function Calls::), but it is up to you to define them, i.e., to tell `awk' what they should do. a8622 1 * Dynamic Typing:: How variable types can change at runtime. d8625 1 a8625 1 File: gawk.info, Node: Definition Syntax, Next: Function Example, Up: User-defined d8628 1 a8628 1 -------------------------- d8632 4 a8635 4 to include sequences of rules _and_ user-defined function definitions. There is no need to put the definition of a function before all uses of the function. This is because `awk' reads the entire program before starting to execute any of it. d8644 4 a8647 5 NAME is the name of the function to define. A valid function name is like a valid variable name: a sequence of letters, digits, and underscores that doesn't start with a digit. Within a single `awk' program, any particular name can only be used as a variable, array, or function. d8653 1 a8653 2 cannot have two parameters with the same name, nor may it have a parameter with the same name as the function itself. d8657 3 a8659 3 should actually _do_. The argument names exist to give the body a way to talk about the arguments; local variables exist to give the body places to keep temporary values. d8662 1 a8662 1 variable names. Instead, the number of arguments supplied when the d8665 1 a8665 1 PARAMETER-LIST are arguments and the rest are local variables. d8672 5 a8676 5 Usually when you write a function, you know how many names you intend to use for arguments and how many you intend to use as local variables. It is conventional to place some extra space between the arguments and the local variables, in order to document how your function is supposed to be used. d8679 1 a8679 1 variable values hide, or "shadow", any variables of the same names used d8690 1 a8690 1 The function body can contain expressions that call functions. They d8692 1 a8692 2 function. When this happens, we say the function is "recursive". The act of a function calling itself is called "recursion". d8697 3 a8699 2 implications. If `gawk' is in POSIX-compatibility mode (*note Options::), then the following statement does _not_ define a function: d8706 3 a8708 3 probably not what is desired. (`awk' accepts this input as syntactically valid, because functions may be used before they are defined in `awk' programs.) d8717 1 a8717 1 ---------------------------- d8720 1 a8720 1 takes a number and prints it in a specific format: d8727 1 a8727 1 To illustrate, here is an `awk' rule that uses our `myprint' function: d8732 1 a8732 2 contain a positive number in our input. Therefore, when given the following: d8743 1 a8743 1 This function deletes all the elements in an array: d8753 6 a8758 10 Delete::). Instead of having to repeat this loop everywhere that you need to clear out an array, your program can just call `delarray'. (This guarantees portability. The use of `delete ARRAY' to delete the contents of an entire array is a nonstandard extension.) The following is an example of a recursive function. It takes a string as an input parameter and returns the string in backwards order. Recursive functions must always have a test that stops the recursion. In this case, the recursion terminates when the starting position is zero, i.e., when there are no more characters left in the string. d8768 1 a8768 1 If this function is in a file named `rev.awk', it can be tested this d8775 5 a8779 4 The C `ctime' function takes a timestamp and returns it in a string, formatted in a well-known fashion. The following example uses the built-in `strftime' function (*note Time Functions::) to create an `awk' version of `ctime': d8796 2 a8797 2 Calling User-Defined Functions ------------------------------ d8800 1 a8800 1 job. A function call is an expression and its value is the value d8804 2 a8805 2 arguments in parentheses. `awk' expressions are what you write in the call for the arguments. Each time the call is executed, these d8812 1 a8812 1 *Caution:* Whitespace characters (spaces and tabs) are not allowed d8819 1 a8819 1 When a function is called, it is given a _copy_ of the values of its d8822 2 a8823 2 does not know this--it only knows what value the argument had. For example, if you write the following code: d8829 5 a8833 4 variable `foo'." Instead, think of the argument as the string value `"bar"'. If the function `myfunc' alters the values of its local variables, this has no effect on any other variables. Thus, if `myfunc' does this: d8842 1 a8842 1 to change its first argument variable `str', it does _not_ change the d8844 1 a8844 1 ended when its value (`"bar"') was computed. If `str' also exists d8849 1 a8849 1 However, when arrays are the parameters to functions, they are _not_ d8853 1 a8853 3 function _are_ visible outside that function. *Note:* Changing an array parameter inside a function can be very d8868 2 a8869 2 prints `a[1] = 1, a[2] = two, a[3] = 3', because `changeit' stores `"two"' in the second element of `a'. d8872 1 a8872 1 been defined. They only report a problem at runtime when the program d8884 3 a8886 3 Because the `if' statement will never be true, it is not really a problem that `foo' has not been defined. Usually, though, it is a problem if a program calls an undefined function. d8888 2 a8889 2 If `--lint' is specified (*note Options::), `gawk' reports calls to undefined functions. d8891 3 a8893 3 Some `awk' implementations generate a runtime error if you use the `next' statement (*note Next Statement::) inside a user-defined function. `gawk' does not have this limitation. d8896 1 a8896 1 File: gawk.info, Node: Return Statement, Next: Dynamic Typing, Prev: Function Caveats, Up: User-defined d8899 1 a8899 1 ---------------------- d8902 3 a8904 3 This statement returns control to the calling part of the `awk' program. It can also be used to return a value for use in the rest of the `awk' program. It looks like this: d8909 1 a8909 1 value is undefined, and therefore, unpredictable. d8914 1 a8914 1 does _not_ warn you if you use the return value of such a function. d8919 2 a8920 2 return any value; simply bear in mind that if you use the return value of such a function, you do so at your own risk. d8922 2 a8923 2 The following is an example of a user-defined function that returns a value for the largest number among the elements of an array: d8936 1 a8936 1 is nothing to stop you from passing more than one argument to `maxelt', d8939 2 a8940 2 to be arguments. You should follow this convention when defining functions. d8942 1 a8942 1 The following program uses the `maxelt' function. It loads an d8946 1 d8964 1 a8964 1 } d8974 2 a8975 2 the program reports (predictably) that `99385' is the largest number in the array. d8978 1 a8978 1 File: gawk.info, Node: Dynamic Typing, Prev: Return Statement, Up: User-defined d8980 2 a8981 2 Functions and Their Effects on Variable Typing ---------------------------------------------- d8983 3 a8985 3 `awk' is a very fluid language. It is possible that `awk' can't tell if an identifier represents a regular variable or an array until runtime. Here is an annotated sample program: d8987 2 a8988 12 function foo(a) { a[1] = 1 # parameter is an array } BEGIN { b = 1 foo(b) # invalid: fatal type mismatch foo(x) # x uninitialized, becomes an array dynamically x = 1 # now not allowed, runtime error } d8990 2 a8991 2 Usually, such things aren't a big issue, but it's worth being aware of them. d8993 1 a8993 5  File: gawk.info, Node: Internationalization, Next: Advanced Features, Prev: Functions, Up: Top Internationalization with `gawk' ******************************** d8995 1 a8995 6 Once upon a time, computer makers wrote software that worked only in English. Eventually, hardware and software vendors noticed that if their systems worked in the native languages of non-English-speaking countries, they were able to sell more systems. As a result, internationalization and localization of programs and software systems became a common practice. d8997 3 a8999 8 Until recently, the ability to provide internationalization was largely restricted to programs written in C and C++. This major node describes the underlying library `gawk' uses for internationalization, as well as how `gawk' makes internationalization features available at the `awk' program level. Having internationalization available at the `awk' level gives software developers additional flexibility--they are no longer required to write in C when internationalization is a requirement. d9003 6 a9008 6 * I18N and L10N:: Internationalization and Localization. * Explaining gettext:: How GNU `gettext' works. * Programmer i18n:: Features for the programmer. * Translator i18n:: Features for the translator. * I18N Example:: A simple i18n example. * Gawk I18N:: `gawk' is also internationalized. d9011 1 a9011 1 File: gawk.info, Node: I18N and L10N, Next: Explaining gettext, Up: Internationalization d9013 2 a9014 2 Internationalization and Localization ===================================== d9016 9 a9024 124 "Internationalization" means writing (or modifying) a program once, in such a way that it can use multiple languages without requiring further source-code changes. "Localization" means providing the data necessary for an internationalized program to work in a particular language. Most typically, these terms refer to features such as the language used for printing error messages, the language used to read responses, and information related to how numerical and monetary values are printed and read.  File: gawk.info, Node: Explaining gettext, Next: Programmer i18n, Prev: I18N and L10N, Up: Internationalization GNU `gettext' ============= The facilities in GNU `gettext' focus on messages; strings printed by a program, either directly or via formatting with `printf' or `sprintf'.(1) When using GNU `gettext', each application has its own "text domain". This is a unique name, such as `kpilot' or `gawk', that identifies the application. A complete application may have multiple components--programs written in C or C++, as well as scripts written in `sh' or `awk'. All of the components use the same text domain. To make the discussion concrete, assume we're writing an application named `guide'. Internationalization consists of the following steps, in this order: 1. The programmer goes through the source for all of `guide''s components and marks each string that is a candidate for translation. For example, `"`-F': option required"' is a good candidate for translation. A table with strings of option names is not (e.g., `gawk''s `--profile' option should remain the same, no matter what the local language). 2. The programmer indicates the application's text domain (`"guide"') to the `gettext' library, by calling the `textdomain' function. 3. Messages from the application are extracted from the source code and collected into a portable object file (`guide.po'), which lists the strings and their translations. The translations are initially empty. The original (usually English) messages serve as the key for lookup of the translations. 4. For each language with a translator, `guide.po' is copied and translations are created and shipped with the application. 5. Each language's `.po' file is converted into a binary message object (`.mo') file. A message object file contains the original messages and their translations in a binary format that allows fast lookup of translations at runtime. 6. When `guide' is built and installed, the binary translation files are installed in a standard place. 7. For testing and development, it is possible to tell `gettext' to use `.mo' files in a different directory than the standard one by using the `bindtextdomain' function. 8. At runtime, `guide' looks up each string via a call to `gettext'. The returned string is the translated string if available, or the original string if not. 9. If necessary, it is possible to access messages from a different text domain than the one belonging to the application, without having to switch the application's default text domain back and forth. In C (or C++), the string marking and dynamic translation lookup are accomplished by wrapping each string in a call to `gettext': printf(gettext("Don't Panic!\n")); The tools that extract messages from source code pull out all strings enclosed in calls to `gettext'. The GNU `gettext' developers, recognizing that typing `gettext' over and over again is both painful and ugly to look at, use the macro `_' (an underscore) to make things easier: /* In the standard header file: */ #define _(str) gettext(str) /* In the program text: */ printf(_("Don't Panic!\n")); This reduces the typing overhead to just three extra characters per string and is considerably easier to read as well. There are locale "categories" for different types of locale-related information. The defined locale categories that `gettext' knows about are: `LC_MESSAGES' Text messages. This is the default category for `gettext' operations, but it is possible to supply a different one explicitly, if necessary. (It is almost never necessary to supply a different category.) `LC_COLLATE' Text-collation information; i.e., how different characters and/or groups of characters sort in a given language. `LC_CTYPE' Character-type information (alphabetic, digit, upper- or lowercase, and so on). This information is accessed via the POSIX character classes in regular expressions, such as `/[[:alnum:]]/' (*note Regexp Operators::). `LC_MONETARY' Monetary information, such as the currency symbol, and whether the symbol goes before or after a number. `LC_NUMERIC' Numeric information, such as which characters to use for the decimal point and the thousands separator.(2) `LC_RESPONSE' Response information, such as how "yes" and "no" appear in the local language, and possibly other information as well. `LC_TIME' Time- and date-related information, such as 12- or 24-hour clock, month printed before or after day in a date, local month abbreviations, and so on. d9026 2 a9027 2 `LC_ALL' All of the above. (Not too useful in the context of `gettext'.) d9029 4 a9032 1 ---------- Footnotes ---------- d9034 4 a9037 4 (1) For some operating systems, the `gawk' port doesn't support GNU `gettext'. This applies most notably to the PC operating systems. As such, these features are not available if you are using one of those operating systems. Sorry. d9039 6 a9044 3 (2) Americans use a comma every three decimal places and a period for the decimal point, while many Europeans do exactly the opposite: `1,234.56' versus `1.234,56'. d9046 3 a9048 2  File: gawk.info, Node: Programmer i18n, Next: Translator i18n, Prev: Explaining gettext, Up: Internationalization d9050 8 a9057 2 Internationalizing `awk' Programs ================================= d9059 4 a9062 2 `gawk' provides the following variables and functions for internationalization: d9064 5 a9068 57 `TEXTDOMAIN' This variable indicates the application's text domain. For compatibility with GNU `gettext', the default value is `"messages"'. `_"your message here"' String constants marked with a leading underscore are candidates for translation at runtime. String constants without a leading underscore are not translated. `dcgettext(STRING [, DOMAIN [, CATEGORY]])' This built-in function returns the translation of STRING in text domain DOMAIN for locale category CATEGORY. The default value for DOMAIN is the current value of `TEXTDOMAIN'. The default value for CATEGORY is `"LC_MESSAGES"'. If you supply a value for CATEGORY, it must be a string equal to one of the known locale categories described in *Note Explaining gettext::. You must also supply a text domain. Use `TEXTDOMAIN' if you want to use the current domain. *Caution:* The order of arguments to the `awk' version of the `dcgettext' function is purposely different from the order for the C version. The `awk' version's order was chosen to be simple and to allow for reasonable `awk'-style default arguments. `dcngettext(STRING1, STRING2, NUMBER [, DOMAIN [, CATEGORY]])' This built-in function returns the plural form used for NUMBER of the translation of STRING1 and STRING2 in text domain DOMAIN for locale category CATEGORY. STRING1 is the English singular variant of a message, and STRING2 the English plural variant of the same message. The default value for DOMAIN is the current value of `TEXTDOMAIN'. The default value for CATEGORY is `"LC_MESSAGES"'. The same remarks as for the `dcgettext' function apply. `bindtextdomain(DIRECTORY [, DOMAIN])' This built-in function allows you to specify the directory in which `gettext' looks for `.mo' files, in case they will not or cannot be placed in the standard locations (e.g., during testing). It returns the directory in which DOMAIN is "bound." The default DOMAIN is the value of `TEXTDOMAIN'. If DIRECTORY is the null string (`""'), then `bindtextdomain' returns the current binding for the given DOMAIN. To use these facilities in your `awk' program, follow the steps outlined in *Note Explaining gettext::, like so: 1. Set the variable `TEXTDOMAIN' to the text domain of your program. This is best done in a `BEGIN' rule (*note BEGIN/END::), or it can also be done via the `-v' command-line option (*note Options::): BEGIN { TEXTDOMAIN = "guide" ... } d9070 3 a9072 33 2. Mark all translatable strings with a leading underscore (`_') character. It _must_ be adjacent to the opening quote of the string. For example: print _"hello, world" x = _"you goofed" printf(_"Number of users is %d\n", nusers) 3. If you are creating strings dynamically, you can still translate them, using the `dcgettext' built-in function: message = nusers " users logged in" message = dcgettext(message, "adminprog") print message Here, the call to `dcgettext' supplies a different text domain (`"adminprog"') in which to find the message, but it uses the default `"LC_MESSAGES"' category. 4. During development, you might want to put the `.mo' file in a private directory for testing. This is done with the `bindtextdomain' built-in function: BEGIN { TEXTDOMAIN = "guide" # our text domain if (Testing) { # where to find our files bindtextdomain("testdir") # joe is in charge of adminprog bindtextdomain("../joe/testdir", "adminprog") } ... } d9074 1 d9076 10 a9085 2 *Note I18N Example::, for an example program showing the steps to create and use translations from `awk'. d9087 6 a9092 2  File: gawk.info, Node: Translator i18n, Next: I18N Example, Prev: Programmer i18n, Up: Internationalization d9094 6 a9099 2 Translating `awk' Programs ========================== d9101 6 a9106 8 Once a program's translatable strings have been marked, they must be extracted to create the initial `.po' file. As part of translation, it is often helpful to rearrange the order in which arguments to `printf' are output. `gawk''s `--gen-po' command-line option extracts the messages and is discussed next. After that, `printf''s ability to rearrange the order for `printf' arguments at runtime is covered. d9108 5 a9112 1 * Menu: d9114 5 a9118 3 * String Extraction:: Extracting marked strings. * Printf Ordering:: Rearranging `printf' arguments. * I18N Portability:: `awk'-level portability issues. d9120 2 a9121 2  File: gawk.info, Node: String Extraction, Next: Printf Ordering, Up: Translator i18n d9123 2 a9124 2 Extracting Marked Strings ------------------------- d9126 3 a9128 14 Once your `awk' program is working, and all the strings have been marked and you've set (and perhaps bound) the text domain, it is time to produce translations. First, use the `--gen-po' command-line option to create the initial `.po' file: $ gawk --gen-po -f guide.awk > guide.po When run with `--gen-po', `gawk' does not execute your program. Instead, it parses it as usual and prints all marked strings to standard output in the format of a GNU `gettext' Portable Object file. Also included in the output are any constant strings that appear as the first argument to `dcgettext' or as the first and second argument to `dcngettext'.(1) *Note I18N Example::, for the full list of steps to go through to create and test translations for `guide'. d9130 7 a9136 1 ---------- Footnotes ---------- d9138 2 a9139 2 (1) Starting with `gettext' version 0.11.5, the `xgettext' utility that comes with GNU `gettext' can handle `.awk' files. d9141 3 a9143 2  File: gawk.info, Node: Printf Ordering, Next: I18N Portability, Prev: String Extraction, Up: Translator i18n d9145 6 a9150 2 Rearranging `printf' Arguments ------------------------------ d9152 8 a9159 2 Format strings for `printf' and `sprintf' (*note Printf::) present a special problem for translation. Consider the following:(1) d9161 7 a9167 2 printf(_"String `%s' has %d characters\n", string, length(string))) d9169 2 a9170 1 A possible German translation for this might be: d9172 4 a9175 1 "%d Zeichen lang ist die Zeichenkette `%s'\n" d9177 14 a9190 4 The problem should be obvious: the order of the format specifications is different from the original! Even though `gettext' can return the translated string at runtime, it cannot change the argument order in the call to `printf'. d9192 6 a9197 3 To solve this problem, `printf' format specificiers may have an additional optional element, which we call a "positional specifier". For example: d9199 3 a9201 1 "%2$d Zeichen lang ist die Zeichenkette `%1$s'\n" d9203 11 a9213 12 Here, the positional specifier consists of an integer count, which indicates which argument to use, and a `$'. Counts are one-based, and the format string itself is _not_ included. Thus, in the following example, `string' is the first argument and `length(string)' is the second: $ gawk 'BEGIN { > string = "Dont Panic" > printf _"%2$d characters live in \"%1$s\"\n", > string, length(string) > }' -| 10 characters live in "Dont Panic" d9215 2 a9216 2 If present, positional specifiers come first in the format specification, before the flags, the field width, and/or the precision. d9218 2 a9219 2 Positional specifiers can be used with the dynamic field width and precision capability: d9221 1 a9221 25 $ gawk 'BEGIN { > printf("%*.*s\n", 10, 20, "hello") > printf("%3$*2$.*1$s\n", 20, 10, "hello") > }' -| hello -| hello *Note:* When using `*' with a positional specifier, the `*' comes first, then the integer position, and then the `$'. This is somewhat counterintutive. `gawk' does not allow you to mix regular format specifiers and those with positional specifiers in the same string: $ gawk 'BEGIN { printf _"%d %3$s\n", 1, 2, "hi" }' error--> gawk: cmd. line:1: fatal: must use `count$' on all formats or none *Note:* There are some pathological cases that `gawk' may fail to diagnose. In such cases, the output may not be what you expect. It's still a bad idea to try mixing them, even if `gawk' doesn't detect it. Although positional specifiers can be used directly in `awk' programs, their primary purpose is to help in producing correct translations of format strings into languages different from the one in which the program is first written. d9225 1 a9225 1 (1) This example is borrowed from the GNU `gettext' manual. d9228 1 a9228 1 File: gawk.info, Node: I18N Portability, Prev: Printf Ordering, Up: Translator i18n d9230 2 a9231 2 `awk' Portability Issues ------------------------ d9233 4 a9236 3 `gawk''s internationalization features were purposely chosen to have as little impact as possible on the portability of `awk' programs that use them to other versions of `awk'. Consider this program: d9238 6 a9243 6 BEGIN { TEXTDOMAIN = "guide" if (Test_Guide) # set with -v bindtextdomain("/test/guide/messages") print _"don't panic!" } d9245 5 a9249 2 As written, it won't work on other versions of `awk'. However, it is actually almost portable, requiring very little change: d9251 5 a9255 2 * Assignments to `TEXTDOMAIN' won't have any effect, since `TEXTDOMAIN' is not special in other `awk' implementations. d9257 2 a9258 4 * Non-GNU versions of `awk' treat marked strings as the concatenation of a variable named `_' with the string following it.(1) Typically, the variable `_' has the null string (`""') as its value, leaving the original string constant as the result. d9260 8 a9267 3 * By defining "dummy" functions to replace `dcgettext', `dcngettext' and `bindtextdomain', the `awk' program can be made to run, but all the messages are output in the original language. For example: d9269 5 a9273 14 function bindtextdomain(dir, domain) { return dir } function dcgettext(string, domain, category) { return string } function dcngettext(string1, string2, number, domain, category) { return (number == 1 ? string1 : string2) } d9275 2 a9276 12 * The use of positional specifications in `printf' or `sprintf' is _not_ portable. To support `gettext' at the C level, many systems' C versions of `sprintf' do support positional specifiers. But it works only if enough arguments are supplied in the function call. Many versions of `awk' pass `printf' formats and arguments unchanged to the underlying C library version of `sprintf', but only one format and argument at a time. What happens if a positional specification is used is anybody's guess. However, since the positional specifications are primarily for use in _translated_ format strings, and since non-GNU `awk's never retrieve the translated string, this should not be a problem in practice. d9278 3 a9280 3 ---------- Footnotes ---------- (1) This is good fodder for an "Obfuscated `awk'" contest. d9283 1 a9283 1 File: gawk.info, Node: I18N Example, Next: Gawk I18N, Prev: Translator i18n, Up: Internationalization d9285 2 a9286 2 A Simple Internationalization Example ===================================== d9288 4 a9291 3 Now let's look at a step-by-step example of how to internationalize and localize a simple `awk' program, using `guide.awk' as our original source: d9293 3 a9295 7 BEGIN { TEXTDOMAIN = "guide" bindtextdomain(".") # for testing print _"Don't Panic" print _"The Answer Is", 42 print "Pardon me, Zaphod who?" } d9297 20 a9316 1 Run `gawk --gen-po' to create the `.po' file: d9318 8 a9325 1 $ gawk --gen-po -f guide.awk > guide.po d9327 4 a9330 63 This produces: #: guide.awk:4 msgid "Don't Panic" msgstr "" #: guide.awk:5 msgid "The Answer Is" msgstr "" This original portable object file is saved and reused for each language into which the application is translated. The `msgid' is the original string and the `msgstr' is the translation. *Note:* Strings not marked with a leading underscore do not appear in the `guide.po' file. Next, the messages must be translated. Here is a translation to a hypothetical dialect of English, called "Mellow":(1) $ cp guide.po guide-mellow.po ADD TRANSLATIONS TO guide-mellow.po ... Following are the translations: #: guide.awk:4 msgid "Don't Panic" msgstr "Hey man, relax!" #: guide.awk:5 msgid "The Answer Is" msgstr "Like, the scoop is" The next step is to make the directory to hold the binary message object file and then to create the `guide.mo' file. The directory layout shown here is standard for GNU `gettext' on GNU/Linux systems. Other versions of `gettext' may use a different layout: $ mkdir en_US en_US/LC_MESSAGES The `msgfmt' utility does the conversion from human-readable `.po' file to machine-readable `.mo' file. By default, `msgfmt' creates a file named `messages'. This file must be renamed and placed in the proper directory so that `gawk' can find it: $ msgfmt guide-mellow.po $ mv messages en_US/LC_MESSAGES/guide.mo Finally, we run the program to test it: $ gawk -f guide.awk -| Hey man, relax! -| Like, the scoop is 42 -| Pardon me, Zaphod who? If the three replacement functions for `dcgettext', `dcngettext' and `bindtextdomain' (*note I18N Portability::) are in a file named `libintl.awk', then we can run `guide.awk' unchanged as follows: $ gawk --posix -f guide.awk -f libintl.awk -| Don't Panic -| The Answer Is 42 -| Pardon me, Zaphod who? d9334 5 a9338 1 (1) Perhaps it would be better if it were called "Hippy." Ah, well. d9341 1 a9341 1 File: gawk.info, Node: Gawk I18N, Prev: I18N Example, Up: Internationalization d9343 2 a9344 2 `gawk' Can Speak Your Language ============================== d9346 4 a9349 38 As of version 3.1, `gawk' itself has been internationalized using the GNU `gettext' package. (GNU `gettext' is described in complete detail in *Note Top::.) As of this writing, the latest version of GNU `gettext' is version 0.11.5 (ftp://ftp.gnu.org/gnu/gettext/gettext-0.11.5.tar.gz). If a translation of `gawk''s messages exists, then `gawk' produces usage messages, warnings, and fatal errors in the local language. On systems that do not use version 2 (or later) of the GNU C library, you should configure `gawk' with the `--with-included-gettext' option before compiling and installing it. *Note Additional Configuration Options::, for more information.  File: gawk.info, Node: Advanced Features, Next: Invoking Gawk, Prev: Internationalization, Up: Top Advanced Features of `gawk' *************************** Write documentation as if whoever reads it is a violent psychopath who knows where you live. Steve English, as quoted by Peter Langston This major node discusses advanced features in `gawk'. It's a bit of a "grab bag" of items that are otherwise unrelated to each other. First, a command-line option allows `gawk' to recognize nondecimal numbers in input data, not just in `awk' programs. Next, two-way I/O, discussed briefly in earlier parts of this Info file, is described in full detail, along with the basics of TCP/IP networking and BSD portal files. Finally, `gawk' can "profile" an `awk' program, making it possible to tune it for performance. *Note Dynamic Extensions::, discusses the ability to dynamically add new built-in functions to `gawk'. As this feature is still immature and likely to change, its description is relegated to an appendix. * Menu: d9351 4 a9354 5 * Nondecimal Data:: Allowing nondecimal input data. * Two-way I/O:: Two-way communications with another process. * TCP/IP Networking:: Using `gawk' for network programming. * Portal Files:: Using `gawk' with BSD portals. * Profiling:: Profiling your `awk' programs. d9357 1 a9357 1 File: gawk.info, Node: Nondecimal Data, Next: Two-way I/O, Up: Advanced Features d9359 2 a9360 2 Allowing Nondecimal Input Data ============================== d9362 2 a9363 2 If you run `gawk' with the `--non-decimal-data' option, you can have nondecimal constants in your input data: d9365 1 a9365 32 $ echo 0123 123 0x123 | > gawk --non-decimal-data '{ printf "%d, %d, %d\n", > $1, $2, $3 }' -| 83, 123, 291 For this feature to work, write your program so that `gawk' treats your data as numeric: $ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }' -| 0123 123 0x123 The `print' statement treats its expressions as strings. Although the fields can act as numbers when necessary, they are still strings, so `print' does not try to treat them numerically. You may need to add zero to a field to force it to be treated as a number. For example: $ echo 0123 123 0x123 | gawk --non-decimal-data ' > { print $1, $2, $3 > print $1 + 0, $2 + 0, $3 + 0 }' -| 0123 123 0x123 -| 83 123 291 Because it is common to have decimal data with leading zeros, and because using it could lead to surprising results, the default is to leave this facility disabled. If you want it, you must explicitly request it. *Caution:* _Use of this option is not recommended._ It can break old programs very badly. Instead, use the `strtonum' function to convert your data (*note Nondecimal-numbers::). This makes your programs easier to write and easier to read, and leads to less surprising results. d9368 1 a9368 1 File: gawk.info, Node: Two-way I/O, Next: TCP/IP Networking, Prev: Nondecimal Data, Up: Advanced Features d9370 2 a9371 2 Two-Way Communications with Another Process =========================================== d9373 12 a9384 87 From: brennan@@whidbey.com (Mike Brennan) Newsgroups: comp.lang.awk Subject: Re: Learn the SECRET to Attract Women Easily Date: 4 Aug 1997 17:34:46 GMT Message-ID: <5s53rm$eca@@news.whidbey.com> On 3 Aug 1997 13:17:43 GMT, Want More Dates??? wrote: >Learn the SECRET to Attract Women Easily > >The SCENT(tm) Pheromone Sex Attractant For Men to Attract Women The scent of awk programmers is a lot more attractive to women than the scent of perl programmers. -- Mike Brennan It is often useful to be able to send data to a separate program for processing and then read the result. This can always be done with temporary files: # write the data for processing tempfile = ("mydata." PROCINFO["pid"]) while (NOT DONE WITH DATA) print DATA | ("subprogram > " tempfile) close("subprogram > " tempfile) # read the results, remove tempfile when done while ((getline newdata < tempfile) > 0) PROCESS newdata APPROPRIATELY close(tempfile) system("rm " tempfile) This works, but not elegantly. Among other things, it requires that the program be run in a directory that cannot be shared among users; for example, `/tmp' will not do, as another user might happen to be using a temporary file with the same name. Starting with version 3.1 of `gawk', it is possible to open a _two-way_ pipe to another process. The second process is termed a "coprocess", since it runs in parallel with `gawk'. The two-way connection is created using the new `|&' operator (borrowed from the Korn shell, `ksh'):(1) do { print DATA |& "subprogram" "subprogram" |& getline results } while (DATA LEFT TO PROCESS) close("subprogram") The first time an I/O operation is executed using the `|&' operator, `gawk' creates a two-way pipeline to a child process that runs the other program. Output created with `print' or `printf' is written to the program's standard input, and output from the program's standard output can be read by the `gawk' program using `getline'. As is the case with processes started by `|', the subprogram can be any program, or pipeline of programs, that can be started by the shell. There are some cautionary items to be aware of: * As the code inside `gawk' currently stands, the coprocess's standard error goes to the same place that the parent `gawk''s standard error goes. It is not possible to read the child's standard error separately. * I/O buffering may be a problem. `gawk' automatically flushes all output down the pipe to the child process. However, if the coprocess does not flush its output, `gawk' may hang when doing a `getline' in order to read the coprocess's results. This could lead to a situation known as "deadlock", where each process is waiting for the other one to do something. It is possible to close just one end of the two-way pipe to a coprocess, by supplying a second argument to the `close' function of either `"to"' or `"from"' (*note Close Files And Pipes::). These strings tell `gawk' to close the end of the pipe that sends data to the process or the end that reads from it, respectively. This is particularly necessary in order to use the system `sort' utility as part of a coprocess; `sort' must read _all_ of its input data before it can produce any output. The `sort' program does not receive an end-of-file indication until `gawk' closes the write end of the pipe. When you have finished writing data to the `sort' utility, you can close the `"to"' end of the pipe, and then start reading sorted data via `getline'. For example: d9386 4 a9389 42 BEGIN { command = "LC_ALL=C sort" n = split("abcdefghijklmnopqrstuvwxyz", a, "") for (i = n; i > 0; i--) print a[i] |& command close(command, "to") while ((command |& getline line) > 0) print "got", line close(command) } This program writes the letters of the alphabet in reverse order, one per line, down the two-way pipe to `sort'. It then closes the write end of the pipe, so that `sort' receives an end-of-file indication. This causes `sort' to sort the data and write the sorted data back to the `gawk' program. Once all of the data has been read, `gawk' terminates the coprocess and exits. As a side note, the assignment `LC_ALL=C' in the `sort' command ensures traditional Unix (ASCII) sorting from `sort'. Beginning with `gawk' 3.1.2, you may use Pseudo-ttys (ptys) for two-way communication instead of pipes, if your system supports them. This is done on a per-command basis, by setting a special element in the `PROCINFO' array (*note Auto-set::), like so: command = "sort -nr" # command, saved in variable for convenience PROCINFO[command, "pty"] = 1 # update PROCINFO print ... |& command # start two-way pipe ... Using ptys avoids the buffer deadlock issues described earlier, at some loss in performance. If your system does not have ptys, or if all the system's ptys are in use, `gawk' automatically falls back to using regular pipes. ---------- Footnotes ---------- (1) This is very different from the same operator in the C shell, `csh'. d9392 1 a9392 1 File: gawk.info, Node: TCP/IP Networking, Next: Portal Files, Prev: Two-way I/O, Up: Advanced Features d9394 2 a9395 2 Using `gawk' for Network Programming ==================================== d9397 18 a9414 43 `EMISTERED': A host is a host from coast to coast, and no-one can talk to host that's close, unless the host that isn't close is busy hung or dead. In addition to being able to open a two-way pipeline to a coprocess on the same system (*note Two-way I/O::), it is possible to make a two-way connection to another process on another system across an IP networking connection. You can think of this as just a _very long_ two-way pipeline to a coprocess. The way `gawk' decides that you want to use TCP/IP networking is by recognizing special file names that begin with `/inet/'. The full syntax of the special file name is `/inet/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'. The components are: PROTOCOL The protocol to use over IP. This must be either `tcp', `udp', or `raw', for a TCP, UDP, or raw IP connection, respectively. The use of TCP is recommended for most applications. *Caution:* The use of raw sockets is not currently supported in version 3.1 of `gawk'. LOCAL-PORT The local TCP or UDP port number to use. Use a port number of `0' when you want the system to pick a port. This is what you should do when writing a TCP or UDP client. You may also use a well-known service name, such as `smtp' or `http', in which case `gawk' attempts to determine the predefined port number using the C `getservbyname' function. REMOTE-HOST The IP address or fully-qualified domain name of the Internet host to which you want to connect. REMOTE-PORT The TCP or UDP port number to use on the given REMOTE-HOST. Again, use `0' if you don't care, or else a well-known service name. d9416 1 a9416 1 Consider the following very simple example: d9418 19 a9436 14 BEGIN { Service = "/inet/tcp/0/localhost/daytime" Service |& getline print $0 close(Service) } This program reads the current date and time from the local system's TCP `daytime' server. It then prints the results and closes the connection. Because this topic is extensive, the use of `gawk' for TCP/IP programming is documented separately. *Note Top::, for a much more complete introduction and discussion, as well as extensive examples. d9439 1 a9439 1 File: gawk.info, Node: Portal Files, Next: Profiling, Prev: TCP/IP Networking, Up: Advanced Features d9441 2 a9442 2 Using `gawk' with BSD Portals ============================= d9444 4 a9447 3 Similar to the `/inet' special files, if `gawk' is configured with the `--enable-portals' option (*note Quick Installation::), then `gawk' treats files whose pathnames begin with `/p' as 4.4 BSD-style portals. d9449 3 a9451 4 When used with the `|&' operator, `gawk' opens the file for two-way communications. The operating system's portal mechanism then manages creating the process associated with the portal and the corresponding communications with the portal's process. d9453 9 a9461 2  File: gawk.info, Node: Profiling, Prev: Portal Files, Up: Advanced Features d9463 2 a9464 2 Profiling Your `awk' Programs ============================= d9466 2 a9467 3 Beginning with version 3.1 of `gawk', you may produce execution traces of your `awk' programs. This is done with a specially compiled version of `gawk', called `pgawk' ("profiling `gawk'"). d9469 2 a9470 4 `pgawk' is identical in every way to `gawk', except that when it has finished running, it creates a profile of your program in a file named `awkprof.out'. Because it is profiling, it also executes up to 45% slower than `gawk' normally does. d9472 2 a9473 3 As shown in the following example, the `--profile' option can be used to change the name of the file where `pgawk' will write the profile: d9475 5 a9479 1 $ pgawk --profile=myprog.prof -f myprog.awk data1 data2 d9481 1 a9481 2 In the above example, `pgawk' places the profile in `myprog.prof' instead of in `awkprof.out'. d9483 1 a9483 8 Regular `gawk' also accepts this option. When called with just `--profile', `gawk' "pretty prints" the program into `awkprof.out', without any execution counts. You may supply an option to `--profile' to change the file name. Here is a sample session showing a simple `awk' program, its input data, and the results from running `pgawk'. First, the `awk' program: BEGIN { print "First BEGIN rule" } d9485 1 a9485 1 END { print "First END rule" } d9487 1 a9487 5 /foo/ { print "matched /foo/, gosh" for (i = 1; i <= 3; i++) sing() } d9489 10 a9498 15 { if (/foo/) print "if is true" else print "else is true" } BEGIN { print "Second BEGIN rule" } END { print "Second END rule" } function sing( dummy) { print "I gotta be me!" } d9500 6 a9505 1 Following is the input data: d9507 2 a9508 5 foo bar baz foo junk d9510 9 a9518 3 Here is the `awkprof.out' that results from running `pgawk' on this program and data (this example also illustrates that `awk' programmers sometimes have to work late): d9520 4 a9523 1 # gawk profile, created Sun Aug 13 00:00:15 2000 d9525 1 a9525 1 # BEGIN block(s) d9527 1 a9527 4 BEGIN { 1 print "First BEGIN rule" 1 print "Second BEGIN rule" } d9529 21 a9549 30 # Rule(s) 5 /foo/ { # 2 2 print "matched /foo/, gosh" 6 for (i = 1; i <= 3; i++) { 6 sing() } } 5 { 5 if (/foo/) { # 2 2 print "if is true" 3 } else { 3 print "else is true" } } # END block(s) END { 1 print "First END rule" 1 print "Second END rule" } # Functions, listed alphabetically 6 function sing(dummy) { 6 print "I gotta be me!" } d9551 2 a9552 2 This example illustrates many of the basic rules for profiling output. The rules are as follows: d9554 15 a9568 3 * The program is printed in the order `BEGIN' rule, pattern/action rules, `END' rule and functions, listed alphabetically. Multiple `BEGIN' and `END' rules are merged together. d9570 1 a9570 6 * Pattern-action rules have two counts. The first count, to the left of the rule, shows how many times the rule's pattern was _tested_. The second count, to the right of the rule's opening left brace in a comment, shows how many times the rule's action was _executed_. The difference between the two indicates how many times the rule's pattern evaluated to false. d9572 3 a9574 5 * Similarly, the count for an `if'-`else' statement shows how many times the condition was tested. To the right of the opening left brace for the `if''s body is a count showing how many times the condition was true. The count for the `else' indicates how many times the test failed. d9576 2 a9577 5 * The count for a loop header (such as `for' or `while') shows how many times the loop test was executed. (Because of this, you can't just look at the count on the first statement in a rule to determine how many times the rule was executed. If the first statement is a loop, the count is misleading.) d9579 2 a9580 4 * For user-defined functions, the count next to the `function' keyword indicates how many times the function was called. The counts next to the statements in the body show how many times those statements were executed. d9582 9 a9590 3 * The layout uses "K&R" style with tabs. Braces are used everywhere, even when the body of an `if', `else', or loop is only a single statement. d9592 7 a9598 5 * Parentheses are used only where needed, as indicated by the structure of the program and the precedence rules. For example, `(3 + 5) * 4' means add three plus five, then multiply the total by four. However, `3 + 5 * 4' has no parentheses, and means `3 + (5 * 4)'. d9600 2 a9601 2 * All string concatenations are parenthesized too. (This could be made a bit smarter.) d9603 1 a9603 4 * Parentheses are used around the arguments to `print' and `printf' only when the `print' or `printf' statement is followed by a redirection. Similarly, if the target of a redirection isn't a scalar, it gets parenthesized. d9605 4 a9608 2 * `pgawk' supplies leading comments in front of the `BEGIN' and `END' rules, the pattern/action rules, and the functions. d9610 18 d9629 6 a9634 7 The profiled version of your program may not look exactly like what you typed when you wrote it. This is because `pgawk' creates the profiled version by "pretty printing" its internal representation of the program. The advantage to this is that `pgawk' can produce a standard representation. The disadvantage is that all source-code comments are lost, as are the distinctions among multiple `BEGIN' and `END' rules. Also, things such as: d9636 6 a9641 1 /foo/ d9643 1 a9643 1 come out as: d9645 4 a9648 2 /foo/ { print $0 d9651 1 a9651 1 which is correct, but possibly surprising. d9653 1 a9653 4 Besides creating profiles when a program has completed, `pgawk' can produce a profile while it is running. This is useful if your `awk' program goes into an infinite loop and you want to see what has been executed. To use this feature, run `pgawk' in the background: d9655 8 a9662 2 $ pgawk -f myprog & [1] 13992 d9664 2 a9665 2 The shell prints a job number and process ID number; in this case, 13992. Use the `kill' command to send the `USR1' signal to `pgawk': d9667 2 a9668 1 $ kill -USR1 13992 d9670 10 a9679 2 As usual, the profiled version of the program is written to `awkprof.out', or to a different file if you use the `--profile' option. d9681 32 a9712 2 Along with the regular profile, as shown earlier, the profile includes a trace of any active functions: d9714 2 a9715 6 # Function Call Stack: # 3. baz # 2. bar # 1. foo # -- main -- d9717 2 a9718 3 You may send `pgawk' the `USR1' signal as many times as you like. Each time, the profile and function call trace are appended to the output profile file. d9720 4 a9723 2 If you use the `HUP' signal instead of the `USR1' signal, `pgawk' produces the profile and the function call trace and then exits. d9725 3 a9727 7 When `pgawk' runs on MS-DOS or MS-Windows, it uses the `INT' and `QUIT' signals for producing the profile and, in the case of the `INT' signal, `pgawk' exits. This is because these systems don't support the `kill' command, so the only signals you can deliver to a program are those generated by the keyboard. The `INT' signal is generated by the `Ctrl-' or `Ctrl-' key, while the `QUIT' signal is generated by the `Ctrl-<\>' key. d9729 2 a9730 2  File: gawk.info, Node: Invoking Gawk, Next: Library Functions, Prev: Advanced Features, Up: Top d9732 34 a9765 2 Running `awk' and `gawk' ************************ d9767 11 a9777 10 This major node covers how to run awk, both POSIX-standard and `gawk'-specific command-line options, and what `awk' and `gawk' do with non-option arguments. It then proceeds to cover how `gawk' searches for source files, obsolete options and/or features, and known bugs in `gawk'. This major node rounds out the discussion of `awk' as a program and as a language. While a number of the options and features described here were discussed in passing earlier in the book, this major node provides the full details. d9779 23 a9801 1 * Menu: d9803 3 a9805 8 * Command Line:: How to run `awk'. * Options:: Command-line options and their meanings. * Other Arguments:: Input file names and variable assignments. * AWKPATH Variable:: Searching directories for `awk' programs. * Obsolete:: Obsolete Options and/or features. * Undocumented:: Undocumented Options and Features. * Known Bugs:: Known Bugs in `gawk'. d9807 2 a9808 2  File: gawk.info, Node: Command Line, Next: Options, Up: Invoking Gawk d9810 1 a9810 2 Invoking `awk' ============== d9812 4 a9815 3 There are two ways to run `awk'--with an explicit program or with one or more program files. Here are templates for both of them; items enclosed in [...] in these templates are optional: d9817 2 a9818 2 awk [OPTIONS] -f progfile [`--'] FILE ... awk [OPTIONS] [`--'] 'PROGRAM' FILE ... d9820 2 a9821 2 Besides traditional one-letter POSIX-style options, `gawk' also supports GNU long options. d9823 5 a9827 1 It is possible to invoke `awk' with an empty program: d9829 7 a9835 1 awk '' datafile1 datafile2 d9837 15 a9851 3 Doing so makes little sense, though; `awk' exits silently when given an empty program. (d.c.) If `--lint' has been specified on the command line, `gawk' issues a warning that the program is empty. d9853 8 a9860 2  File: gawk.info, Node: Options, Next: Other Arguments, Prev: Command Line, Up: Invoking Gawk d9862 3 a9864 2 Command-Line Options ==================== d9866 2 a9867 8 Options begin with a dash and consist of a single character. GNU-style long options consist of two dashes and a keyword. The keyword can be abbreviated, as long as the abbreviation allows the option to be uniquely identified. If the option takes an argument, then the keyword is either immediately followed by an equals sign (`=') and the argument's value, or the keyword and the argument's value are separated by whitespace. If a particular option with a value is given more than once, it is the last value that counts. d9869 2 a9870 3 Each long option for `gawk' has a corresponding POSIX-style option. The long and short options are interchangeable in all contexts. The options and their meanings are as follows: d9872 58 a9929 3 `-F FS' `--field-separator FS' Sets the `FS' variable to FS (*note Field Separators::). d9931 5 a9935 4 `-f SOURCE-FILE' `--file SOURCE-FILE' Indicates that the `awk' program is to be found in SOURCE-FILE instead of in the first non-option argument. d9937 8 a9944 5 `-v VAR=VAL' `--assign VAR=VAL' Sets the variable VAR to the value VAL _before_ execution of the program begins. Such variable values are available inside the `BEGIN' rule (*note Other Arguments::). d9946 70 a10015 3 The `-v' option can only set one variable, but it can be used more than once, setting another variable each time, like this: `awk -v foo=1 -v bar=2 ...'. d10017 80 a10096 15 *Caution:* Using `-v' to set the values of the built-in variables may lead to surprising results. `awk' will reset the values of those variables as it needs to, possibly ignoring any predefined value you may have given. `-mf N' `-mr N' Sets various memory limits to the value N. The `f' flag sets the maximum number of fields and the `r' flag sets the maximum record size. These two flags and the `-m' option are from the Bell Laboratories research version of Unix `awk'. They are provided for compatibility but otherwise ignored by `gawk', since `gawk' has no predefined limits. (The Bell Laboratories `awk' no longer needs these options; it continues to accept them to avoid breaking old programs.) d10098 1 a10098 6 `-W GAWK-OPT' Following the POSIX standard, implementation-specific options are supplied as arguments to the `-W' option. These options also have corresponding GNU-style long options. Note that the long options may be abbreviated, as long as the abbreviations remain unique. The full list of `gawk'-specific options is provided next. d10100 10 a10109 5 `--' Signals the end of the command-line options. The following arguments are not treated as options even if they begin with `-'. This interpretation of `--' follows the POSIX argument parsing conventions. d10111 26 a10136 3 This is useful if you have file names that start with `-', or in shell scripts, if you have file names that will be specified by the user that could start with `-'. d10138 1 a10138 3 The previous list described options mandated by the POSIX standard, as well as options available in the Bell Laboratories version of `awk'. The following list describes `gawk'-specific options: d10140 2 a10141 9 `-W compat' `-W traditional' `--compat' `--traditional' Specifies "compatibility mode", in which the GNU extensions to the `awk' language are disabled, so that `gawk' behaves just like the Bell Laboratories research version of Unix `awk'. `--traditional' is the preferred form of this option. *Note POSIX/GNU::, which summarizes the extensions. Also see *Note Compatibility Mode::. d10143 2 a10144 4 `-W copyright' `--copyright' Print the short version of the General Public License and then exit. d10146 2 a10147 4 `-W copyleft' `--copyleft' Just like `--copyright'. This option may disappear in a future version of `gawk'. d10149 6 a10154 20 `-W dump-variables[=FILE]' `--dump-variables[=FILE]' Prints a sorted list of global variables, their types, and final values to FILE. If no FILE is provided, `gawk' prints this list to the file named `awkvars.out' in the current directory. Having a list of all global variables is a good way to look for typographical errors in your programs. You would also use this option if you have a large program with a lot of functions, and you want to be sure that your functions don't inadvertently use global variables that you meant to be local. (This is a particularly easy mistake to make with simple variable names like `i', `j', etc.) `-W gen-po' `--gen-po' Analyzes the source program and generates a GNU `gettext' Portable Object file on standard output for all string constants that have been marked for translation. *Note Internationalization::, for information about this option. d10156 3 a10158 6 `-W help' `-W usage' `--help' `--usage' Prints a "usage" message summarizing the short and long style options that `gawk' accepts and then exit. d10160 61 a10220 11 `-W lint[=fatal]' `--lint[=fatal]' Warns about constructs that are dubious or nonportable to other `awk' implementations. Some warnings are issued when `gawk' first reads your program. Others are issued at runtime, as your program executes. With an optional argument of `fatal', lint warnings become fatal errors. This may be drastic, but its use will certainly encourage the development of cleaner `awk' programs. With an optional argument of `invalid', only warnings about things that are actually invalid are issued. (This is not fully implemented yet.) d10222 3 a10224 4 `-W lint-old' `--lint-old' Warns about constructs that are not available in the original version of `awk' from Version 7 Unix (*note V7/SVR3.1::). d10226 4 a10229 4 `-W non-decimal-data' `--non-decimal-data' Enable automatic interpretation of octal and hexadecimal values in input data (*note Nondecimal Data::). d10231 2 a10232 2 *Caution:* This option can severely break old programs. Use with care. d10234 2 a10235 5 `-W posix' `--posix' Operates in strict POSIX mode. This disables all `gawk' extensions (just like `--traditional') and adds the following additional restrictions: d10237 9 a10245 2 * `\x' escape sequences are not recognized (*note Escape Sequences::). d10247 5 a10251 2 * Newlines do not act as whitespace to separate fields when `FS' is equal to a single space (*note Fields::). d10253 20 a10272 2 * Newlines are not allowed after `?' or `:' (*note Conditional Exp::). d10274 2 a10275 2 * The synonym `func' for the keyword `function' is not recognized (*note Definition Syntax::). d10277 16 a10292 7 * The `**' and `**=' operators cannot be used in place of `^' and `^=' (*note Arithmetic Ops::, and also *note Assignment Ops::). * Specifying `-Ft' on the command-line does not set the value of `FS' to be a single TAB character (*note Field Separators::). d10294 6 a10299 2 * The `fflush' built-in function is not supported (*note I/O Functions::). d10301 15 a10315 3 If you supply both `--traditional' and `--posix' on the command line, `--posix' takes precedence. `gawk' also issues a warning if both options are supplied. d10317 2 a10318 11 `-W profile[=FILE]' `--profile[=FILE]' Enable profiling of `awk' programs (*note Profiling::). By default, profiles are created in a file named `awkprof.out'. The optional FILE argument allows you to specify a different file name for the profile file. When run with `gawk', the profile is just a "pretty printed" version of the program. When run with `pgawk', the profile contains execution counts for each statement in the program in the left margin, and function call counts for each function. d10320 2 a10321 6 `-W re-interval' `--re-interval' Allows interval expressions (*note Regexp Operators::) in regexps. Because interval expressions were traditionally not available in `awk', `gawk' does not provide them by default. This prevents old `awk' programs from breaking. d10323 2 a10324 7 `-W source PROGRAM-TEXT' `--source PROGRAM-TEXT' Allows you to mix source code in files with source code that you enter on the command line. Program source code is taken from the PROGRAM-TEXT. This is particularly useful when you have library functions that you want to use from your command-line programs (*note AWKPATH Variable::). d10326 18 a10343 6 `-W version' `--version' Prints version information for this particular copy of `gawk'. This allows you to determine if your copy of `gawk' is up to date with respect to whatever the Free Software Foundation is currently distributing. It is also useful for bug reports (*note Bugs::). d10345 4 a10348 2 As long as program text has been supplied, any other options are flagged as invalid with a warning message but are otherwise ignored. d10350 3 a10352 4 In compatibility mode, as a special case, if the value of FS supplied to the `-F' option is `t', then `FS' is set to the TAB character (`"\t"'). This is true only for `--traditional' and not for `--posix' (*note Field Separators::). d10354 3 a10356 14 The `-f' option may be used more than once on the command line. If it is, `awk' reads its program source from all of the named files, as if they had been concatenated together into one big file. This is useful for creating libraries of `awk' functions. These functions can be written once and then retrieved from a standard place, instead of having to be included into each individual program. (As mentioned in *Note Definition Syntax::, function names must be unique.) Library functions can still be used, even if the program is entered at the terminal, by specifying `-f /dev/tty'. After typing your program, type `Ctrl-d' (the end-of-file character) to terminate it. (You may also use `-f -' to read program source from the standard input but then you will not be able to also use the standard input as a source of data.) d10358 5 a10362 5 Because it is clumsy using the standard `awk' mechanisms to mix source file and command-line `awk' programs, `gawk' provides the `--source' option. This does not require you to pre-empt the standard input for your source code; it allows you to easily mix command-line and library source code (*note AWKPATH Variable::). d10364 2 a10365 3 If no `-f' or `--source' option is specified, then `gawk' uses the first non-option command-line argument as the text of the program source code. d10367 3 a10369 9 If the environment variable `POSIXLY_CORRECT' exists, then `gawk' behaves in strict POSIX mode, exactly as if you had supplied the `--posix' command-line option. Many GNU programs look for this environment variable to turn on strict POSIX mode. If `--lint' is supplied on the command line and `gawk' turns on POSIX mode because of `POSIXLY_CORRECT', then it issues a warning message indicating that POSIX mode is in effect. You would typically set this variable in your shell's startup file. For a Bourne-compatible shell (such as `bash'), you would add these lines to the `.profile' file in your home directory: d10371 2 a10372 2 POSIXLY_CORRECT=true export POSIXLY_CORRECT d10374 4 a10377 2 For a `csh'-compatible shell,(1) you would add this line to the `.login' file in your home directory: d10379 3 a10381 1 setenv POSIXLY_CORRECT true d10383 2 a10384 3 Having `POSIXLY_CORRECT' set is not recommended for daily use, but it is good for testing the portability of your programs to other environments. d10386 28 a10413 1 ---------- Footnotes ---------- d10415 3 a10417 1 (1) Not recommended. d10419 7 a10425 2  File: gawk.info, Node: Other Arguments, Next: AWKPATH Variable, Prev: Options, Up: Invoking Gawk d10427 1 a10427 2 Other Command-Line Arguments ============================ d10429 21 a10449 5 Any additional arguments on the command line are normally treated as input files to be processed in the order specified. However, an argument that has the form `VAR=VALUE', assigns the value VALUE to the variable VAR--it does not specify a file at all. (This was discussed earlier in *Note Assignment Options::.) d10451 6 a10456 6 All these arguments are made available to your `awk' program in the `ARGV' array (*note Built-in Variables::). Command-line options and the program text (if present) are omitted from `ARGV'. All other arguments, including variable assignments, are included. As each element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to the index in `ARGV' of the current element. d10458 14 a10471 5 The distinction between file name arguments and variable-assignment arguments is made when `awk' is about to open the next input file. At that point in execution, it checks the file name to see whether it is really a variable assignment; if so, `awk' sets the variable instead of reading a file. d10473 3 a10475 5 Therefore, the variables actually receive the given values after all previously specified files have been read. In particular, the values of variables assigned in this fashion are _not_ available inside a `BEGIN' rule (*note BEGIN/END::), because such rules are run before `awk' begins scanning the argument list. d10477 5 a10481 2 The variable values given on the command line are processed for escape sequences (*note Escape Sequences::). (d.c.) d10483 5 a10487 8 In some earlier implementations of `awk', when a variable assignment occurred before any file names, the assignment would happen _before_ the `BEGIN' rule was executed. `awk''s behavior was thus inconsistent; some command-line assignments were available inside the `BEGIN' rule, while others were not. Unfortunately, some applications came to depend upon this "feature." When `awk' was changed to be more consistent, the `-v' option was added to accommodate applications that depended upon the old behavior. d10489 16 a10504 5 The variable assignment feature is most useful for assigning to variables such as `RS', `OFS', and `ORS', which control input and output formats before scanning the data files. It is also useful for controlling state if multiple passes are needed over a data file. For example: d10506 9 a10514 2 awk 'pass == 1 { PASS 1 STUFF } pass == 2 { PASS 2 STUFF }' pass=1 mydata pass=2 mydata d10516 4 a10519 3 Given the variable assignment feature, the `-F' option for setting the value of `FS' is not strictly necessary. It remains for historical compatibility. d10521 6 a10526 2  File: gawk.info, Node: AWKPATH Variable, Next: Obsolete, Prev: Other Arguments, Up: Invoking Gawk d10528 3 a10530 2 The `AWKPATH' Environment Variable ================================== d10532 9 a10540 7 The previous minor node described how `awk' program files can be named on the command-line with the `-f' option. In most `awk' implementations, you must supply a precise path name for each program file, unless the file is in the current directory. But in `gawk', if the file name supplied to the `-f' option does not contain a `/', then `gawk' searches a list of directories (called the "search path"), one by one, looking for a file with the specified name. d10542 7 a10548 18 The search path is a string consisting of directory names separated by colons. `gawk' gets its search path from the `AWKPATH' environment variable. If that variable does not exist, `gawk' uses a default path, `.:/usr/local/share/awk'.(1) (Programs written for use by system administrators should use an `AWKPATH' variable that does not include the current directory, `.'.) The search path feature is particularly useful for building libraries of useful `awk' functions. The library files can be placed in a standard directory in the default path and then specified on the command line with a short file name. Otherwise, the full file name would have to be typed for each file. By using both the `--source' and `-f' options, your command-line `awk' programs can use facilities in `awk' library files (*note Library Functions::). Path searching is not done if `gawk' is in compatibility mode. This is true for both `--traditional' and `--posix'. *Note Options::. d10550 7 a10556 8 *Note:* If you want files in the current directory to be found, you must include the current directory in the path, either by including `.' explicitly in the path or by writing a null entry in the path. (A null entry is indicated by starting or ending the path with a colon or by placing two colons next to each other (`::').) If the current directory is not included in the path, then files cannot be found in the current directory. This path search mechanism is identical to the shell's. d10558 6 a10563 4 Starting with version 3.0, if `AWKPATH' is not defined in the environment, `gawk' places its default search path into `ENVIRON["AWKPATH"]'. This makes it easy to determine the actual search path that `gawk' will use from within an `awk' program. d10565 15 a10579 5 While you can change `ENVIRON["AWKPATH"]' within your `awk' program, this has no effect on the running program's behavior. This makes sense: the `AWKPATH' environment variable is used to find the program source files. Once your program is running, all the files have been found, and `gawk' no longer needs to use `AWKPATH'. d10581 5 a10585 1 ---------- Footnotes ---------- d10587 2 a10588 4 (1) Your version of `gawk' may use a different directory; it will depend upon how `gawk' was built and installed. The actual directory is the value of `$(datadir)' generated when `gawk' was configured. You probably don't need to worry about this, though. d10590 15 a10604 5  File: gawk.info, Node: Obsolete, Next: Undocumented, Prev: AWKPATH Variable, Up: Invoking Gawk Obsolete Options and/or Features ================================ d10606 2 a10607 4 This minor node describes features and/or command-line options from previous releases of `gawk' that are either not available in the current version or that are still supported but deprecated (meaning that they will _not_ be in the next release). d10609 2 a10610 11 For version 3.1 of `gawk', there are no deprecated command-line options from the previous version of `gawk'. The use of `next file' (two words) for `nextfile' was deprecated in `gawk' 3.0 but still worked. Starting with version 3.1, the two-word usage is no longer accepted. The process-related special files described in *Note Special Process::, work as described, but are now considered deprecated. `gawk' prints a warning message every time they are used. (Use `PROCINFO' instead; see *Note Auto-set::.) They will be removed from the next release of `gawk'. d10613 1 a10613 1 File: gawk.info, Node: Undocumented, Next: Known Bugs, Prev: Obsolete, Up: Invoking Gawk d10615 2 a10616 2 Undocumented Options and Features ================================= d10618 10 a10627 2 Use the Source, Luke! Obi-Wan d10629 6 a10634 1 This minor node intentionally left blank. d10636 13 a10648 2  File: gawk.info, Node: Known Bugs, Prev: Undocumented, Up: Invoking Gawk d10650 29 a10678 2 Known Bugs in `gawk' ==================== d10680 3 a10682 3 * The `-F' option for changing the value of `FS' (*note Options::) is not necessary given the command-line variable assignment feature; it remains only for backward compatibility. d10684 2 a10685 4 * Syntactically invalid single-character programs tend to overflow the parse stack, generating a rather unhelpful message. Such programs are surprisingly difficult to diagnose in the completely general case, and the effort to do so really is not worth it. d10687 3 a10689 2  File: gawk.info, Node: Library Functions, Next: Sample Programs, Prev: Invoking Gawk, Up: Top d10691 2 a10692 2 A Library of `awk' Functions **************************** d10694 2 a10695 28 *Note User-defined::, describes how to write your own `awk' functions. Writing functions is important, because it allows you to encapsulate algorithms and program tasks in a single place. It simplifies programming, making program development more manageable, and making programs more readable. One valuable way to learn a new programming language is to _read_ programs in that language. To that end, this major node and *Note Sample Programs::, provide a good-sized body of code for you to read, and hopefully, to learn from. This major node presents a library of useful `awk' functions. Many of the sample programs presented later in this Info file use these functions. The functions are presented here in a progression from simple to complex. *Note Extract Program::, presents a program that you can use to extract the source code for these example library functions and programs from the Texinfo source for this Info file. (This has already been done as part of the `gawk' distribution.) If you have written one or more useful, general-purpose `awk' functions and would like to contribute them to the author's collection of `awk' programs, see *Note How To Contribute::, for more information. The programs in this major node and in *Note Sample Programs::, freely use features that are `gawk'-specific. Rewriting these programs for different implementations of awk is pretty straightforward. d10697 3 a10699 3 Diagnostic error messages are sent to `/dev/stderr'. Use `| "cat 1>&2"' instead of `> "/dev/stderr"' if your system does not have a `/dev/stderr', or if you cannot use `gawk'. d10701 3 a10703 8 A number of programs use `nextfile' (*note Nextfile Statement::) to skip any remaining input in the input file. *Note Nextfile Function::, shows you how to write a function that does the same thing. Finally, some of the programs choose to ignore upper- and lowercase distinctions in their input. They do so by assigning one to `IGNORECASE'. You can achieve almost the same effect(1) by adding the following rule to the beginning of the program: d10705 3 a10707 2 # ignore case { $0 = tolower($0) } d10709 1 a10709 2 Also, verify that all regexp and string constants used in comparisons use only lowercase letters. d10711 10 a10720 1 * Menu: d10722 3 a10724 9 * Library Names:: How to best name private global variables in library functions. * General Functions:: Functions that are of general use. * Data File Management:: Functions for managing command-line data files. * Getopt Function:: A function for processing command-line arguments. * Passwd Functions:: Functions for getting user information. * Group Functions:: Functions for getting group information. d10726 31 a10756 1 ---------- Footnotes ---------- d10758 4 a10761 3 (1) The effects are not identical. Output of the transformed record will be in all lowercase, while `IGNORECASE' preserves the original contents of the input record. d10763 13 a10775 2  File: gawk.info, Node: Library Names, Next: General Functions, Up: Library Functions d10777 5 a10781 2 Naming Library Function Global Variables ======================================== d10783 7 a10789 4 Due to the way the `awk' language evolved, variables are either "global" (usable by the entire program) or "local" (usable just by a specific function). There is no intermediate state analogous to `static' variables in C. d10791 3 a10793 5 Library functions often need to have global variables that they can use to preserve state information between calls to the function--for example, `getopt''s variable `_opti' (*note Getopt Function::). Such variables are called "private", since the only functions that need to use them are the ones in the library. d10795 7 a10801 5 When writing a library function, you should try to choose names for your private variables that will not conflict with any variables used by either another library function or a user's main program. For example, a name like `i' or `j' is not a good choice, because user programs often use variable names like these for their own purposes. d10803 3 a10805 5 The example programs shown in this major node all start the names of their private variables with an underscore (`_'). Users generally don't use leading underscores in their variable names, so this convention immediately decreases the chances that the variable name will be accidentally shared with the user's program. d10807 7 a10813 7 In addition, several of the library functions use a prefix that helps indicate what function or set of functions use the variables--for example, `_pw_byname' in the user database routines (*note Passwd Functions::). This convention is recommended, since it even further decreases the chance of inadvertent conflict among variable names. Note that this convention is used equally well for variable names and for private function names as well.(1) d10815 3 a10817 12 As a final note on variable naming, if a function makes global variables available for use by a main program, it is a good convention to start that variable's name with a capital letter--for example, `getopt''s `Opterr' and `Optind' variables (*note Getopt Function::). The leading capital letter indicates that it is global, while the fact that the variable name is not all capital letters indicates that the variable is not one of `awk''s built-in variables, such as `FS'. It is also important that _all_ variables in library functions that do not need to save state are, in fact, declared local.(2) If this is not done, the variable could accidentally be used in the user's program, leading to bugs that are very difficult to track down: d10819 1 a10819 1 function lib_func(x, y, l1, l2) d10821 1 a10821 3 ... USE VARIABLE some_var # some_var should be local ... # but is not by oversight d10824 2 a10825 12 A different convention, common in the Tcl community, is to use a single associative array to hold the values needed by the library function(s), or "package." This significantly decreases the number of actual global names in use. For example, the functions described in *Note Passwd Functions::, might have used array elements `PW_data["inited"]', `PW_data["total"]', `PW_data["count"]', and `PW_data["awklib"]', instead of `_pw_inited', `_pw_awklib', `_pw_total', and `_pw_count'. The conventions presented in this minor node are exactly that: conventions. You are not required to write your programs this way--we merely recommend that you do so. d10827 10 a10836 1 ---------- Footnotes ---------- d10838 7 a10844 4 (1) While all the library routines could have been rewritten to use this convention, this was not done, in order to show how my own `awk' programming style has evolved and to provide some basis for this discussion. d10846 2 a10847 2 (2) `gawk''s `--dump-variables' command-line option is useful for verifying this. d10850 1 a10850 1 File: gawk.info, Node: General Functions, Next: Data File Management, Prev: Library Names, Up: Library Functions d10852 2 a10853 2 General Programming =================== d10855 8 a10862 2 This minor node presents a number of functions that are of general programming use. d10864 1 a10864 1 * Menu: d10866 34 a10899 11 * Nextfile Function:: Two implementations of a `nextfile' function. * Assert Function:: A function for assertions in `awk' programs. * Round Function:: A function for rounding if `sprintf' does not do it correctly. * Cliff Random Function:: The Cliff Random Number Generator. * Ordinal Functions:: Functions for using characters as numbers and vice versa. * Join Function:: A function to join an array into a string. * Gettimeofday Function:: A function to get formatted times. d10901 2 a10902 2  File: gawk.info, Node: Nextfile Function, Next: Assert Function, Up: General Functions d10904 2 a10905 2 Implementing `nextfile' as a Function ------------------------------------- d10907 15 a10921 5 The `nextfile' statement, presented in *Note Nextfile Statement::, is a `gawk'-specific extension--it is not available in most other implementations of `awk'. This minor node shows two versions of a `nextfile' function that you can use to simulate `gawk''s `nextfile' statement if you cannot use `gawk'. d10923 1 a10923 1 A first attempt at writing a `nextfile' function is as follows: d10925 8 a10932 5 # nextfile --- skip remaining records in current file # this should be read in before the "main" awk program function nextfile() { _abandon_ = FILENAME; next } _abandon_ == FILENAME { next } d10934 3 a10936 7 Because it supplies a rule that must be executed first, this file should be included before the main program. This rule compares the current data file's name (which is always in the `FILENAME' variable) to a private variable named `_abandon_'. If the file name matches, then the action part of the rule executes a `next' statement to go on to the next record. (The use of `_' in the variable name is a convention. It is discussed more fully in *Note Library Names::.) d10938 31 a10968 20 The use of the `next' statement effectively creates a loop that reads all the records from the current data file. The end of the file is eventually reached and a new data file is opened, changing the value of `FILENAME'. Once this happens, the comparison of `_abandon_' to `FILENAME' fails, and execution continues with the first rule of the "real" program. The `nextfile' function itself simply sets the value of `_abandon_' and then executes a `next' statement to start the loop. This initial version has a subtle problem. If the same data file is listed _twice_ on the commandline, one right after the other or even with just a variable assignment between them, this code skips right through the file a second time, even though it should stop when it gets to the end of the first occurrence. A second version of `nextfile' that remedies this problem is shown here: # nextfile --- skip remaining records in current file # correctly handle successive occurrences of the same file # this should be read in before the "main" awk program d10970 7 a10976 1 function nextfile() { _abandon_ = FILENAME; next } d10978 8 a10985 5 _abandon_ == FILENAME { if (FNR == 1) _abandon_ = "" else next d10988 4 a10991 13 The `nextfile' function has not changed. It makes `_abandon_' equal to the current file name and then executes a `next' statement. The `next' statement reads the next record and increments `FNR' so that `FNR' is guaranteed to have a value of at least two. However, if `nextfile' is called for the last record in the file, then `awk' closes the current data file and moves on to the next one. Upon doing so, `FILENAME' is set to the name of the new file and `FNR' is reset to one. If this next file is the same as the previous one, `_abandon_' is still equal to `FILENAME'. However, `FNR' is equal to one, telling us that this is a new occurrence of the file and not the one we were reading when the `nextfile' function was executed. In that case, `_abandon_' is reset to the empty string, so that further executions of this rule fail (until the next time that `nextfile' is called). d10993 6 a10998 2 If `FNR' is not one, then we are still in the original data file and the program executes a `next' statement to skip through it. d11000 5 a11004 12 An important question to ask at this point is: given that the functionality of `nextfile' can be provided with a library file, why is it built into `gawk'? Adding features for little reason leads to larger, slower programs that are harder to maintain. The answer is that building `nextfile' into `gawk' provides significant gains in efficiency. If the `nextfile' function is executed at the beginning of a large data file, `awk' still has to scan the entire file, splitting it up into records, just to skip over it. The built-in `nextfile' can simply close the file immediately and proceed to the next one, which saves a lot of time. This is particularly important in `awk', because `awk' programs are generally I/O-bound (i.e., they spend most of their time doing input and output, instead of performing computations). d11006 3 a11008 2  File: gawk.info, Node: Assert Function, Next: Round Function, Prev: Nextfile Function, Up: General Functions d11010 2 a11011 2 Assertions ---------- d11013 10 a11022 9 When writing large programs, it is often useful to know that a condition or set of conditions is true. Before proceeding with a particular computation, you make a statement about what you believe to be the case. Such a statement is known as an "assertion". The C language provides an `' header file and corresponding `assert' macro that the programmer can use to make assertions. If an assertion fails, the `assert' macro arranges to print a diagnostic message describing the condition that should have been true but was not, and then it kills the program. In C, using `assert' looks this: d11024 1 a11024 3 #include int myfunc(int a, double b) d11026 4 a11029 2 assert(a <= 5 && b >= 17.1); ... d11032 3 a11034 1 If the assertion fails, the program prints a message similar to this: d11036 7 a11042 1 prog.c:5: assertion failed: a <= 5 && b >= 17.1 d11044 2 a11045 4 The C language makes it possible to turn the condition into a string for use in printing the diagnostic message. This is not possible in `awk', so this `assert' function also requires a string version of the condition that is being tested. Following is the function: d11047 1 a11047 2 # assert --- assert that a condition is true. Otherwise exit. function assert(condition, string) d11049 4 a11052 6 if (! condition) { printf("%s:%d: assertion failed: %s\n", FILENAME, FNR, string) > "/dev/stderr" _assert_exit = 1 exit 1 } d11054 11 a11064 4 END { if (_assert_exit) exit 1 d11067 2 a11068 6 The `assert' function tests the `condition' parameter. If it is false, it prints a message to standard error, using the `string' parameter to describe the failed condition. It then sets the variable `_assert_exit' to one and executes the `exit' statement. The `exit' statement jumps to the `END' rule. If the `END' rules finds `_assert_exit' to be true, it exits immediately. d11070 1 a11070 9 The purpose of the test in the `END' rule is to keep any other `END' rules from running. When an assertion fails, the program should exit immediately. If no assertions fail, then `_assert_exit' is still false when the `END' rule is run normally, and the rest of the program's `END' rules execute. For all of this to work correctly, `assert.awk' must be the first source file read by `awk'. The function can be used in a program in the following way: function myfunc(a, b) d11072 1 a11072 2 assert(a <= 5 && b >= 17.1, "a <= 5 && b >= 17.1") ... d11075 2 a11076 1 If the assertion fails, you see a message similar to the following: d11078 4 a11081 1 mydata:1357: assertion failed: a <= 5 && b >= 17.1 d11083 3 a11085 7 There is a small problem with this version of `assert'. An `END' rule is automatically added to the program calling `assert'. Normally, if a program consists of just a `BEGIN' rule, the input files and/or standard input are not read. However, now that the program has an `END' rule, `awk' attempts to read the input data files or standard input (*note Using BEGIN/END::), most likely causing the program to hang as it waits for input. d11087 2 a11088 2 There is a simple workaround to this: make sure the `BEGIN' rule always ends with an `exit' statement. d11091 30 a11120 1 File: gawk.info, Node: Round Function, Next: Cliff Random Function, Prev: Assert Function, Up: General Functions d11122 14 a11135 2 Rounding Numbers ---------------- d11137 13 a11149 9 The way `printf' and `sprintf' (*note Printf::) perform rounding often depends upon the system's C `sprintf' subroutine. On many machines, `sprintf' rounding is "unbiased," which means it doesn't always round a trailing `.5' up, contrary to naive expectations. In unbiased rounding, `.5' rounds to even, rather than always up, so 1.5 rounds to 2 but 4.5 rounds to 4. This means that if you are using a format that does rounding (e.g., `"%.0f"'), you should check what your system does. The following function does traditional rounding; it might be useful if your awk's `printf' does unbiased rounding: d11151 1 a11151 2 # round.awk --- do normal rounding function round(x, ival, aval, fraction) d11153 3 a11155 21 ival = int(x) # integer part, int() truncates # see if fractional part if (ival == x) # no fraction return x if (x < 0) { aval = -x # absolute value ival = int(aval) fraction = aval - ival if (fraction >= .5) return int(x) - 1 # -2.5 --> -3 else return int(x) # -2.3 --> -2 } else { fraction = x - ival if (fraction >= .5) return ival + 1 else return ival } d11157 13 a11169 3 # test harness { print $0, round($0) } d11172 4 a11175 1 File: gawk.info, Node: Cliff Random Function, Next: Ordinal Functions, Prev: Round Function, Up: General Functions d11177 2 a11178 2 The Cliff Random Number Generator --------------------------------- d11180 2 a11181 20 The Cliff random number generator(1) is a very simple random number generator that "passes the noise sphere test for randomness by showing no structure." It is easily programmed, in less than 10 lines of `awk' code: # cliff_rand.awk --- generate Cliff random numbers BEGIN { _cliff_seed = 0.1 } function cliff_rand() { _cliff_seed = (100 * log(_cliff_seed)) % 1 if (_cliff_seed < 0) _cliff_seed = - _cliff_seed return _cliff_seed } This algorithm requires an initial "seed" of 0.1. Each new value uses the current seed as input for the calculation. If the built-in `rand' function (*note Numeric Functions::) isn't random enough, you might try using this function instead. d11183 1 a11183 1 ---------- Footnotes ---------- d11185 2 a11186 1 (1) `http://mathworld.wolfram.com/CliffRandomNumberGenerator.hmtl' d11189 19 a11207 1 File: gawk.info, Node: Ordinal Functions, Next: Join Function, Prev: Cliff Random Function, Up: General Functions d11209 7 a11215 2 Translating Between Characters and Numbers ------------------------------------------ d11217 2 a11218 4 One commercial implementation of `awk' supplies a built-in function, `ord', which takes a character and returns the numeric value for that character in the machine's character set. If the string passed to `ord' has more than one character, only the first one is used. d11220 2 a11221 4 The inverse of this function is `chr' (from the function of the same name in Pascal), which takes a number and returns the corresponding character. Both functions are written very nicely in `awk'; there is no real reason to build them into the `awk' interpreter: d11223 6 a11228 27 # ord.awk --- do ord and chr # Global identifiers: # _ord_: numerical values indexed by characters # _ord_init: function to initialize _ord_ BEGIN { _ord_init() } function _ord_init( low, high, i, t) { low = sprintf("%c", 7) # BEL is ascii 7 if (low == "\a") { # regular ascii low = 0 high = 127 } else if (sprintf("%c", 128 + 7) == "\a") { # ascii, mark parity low = 128 high = 255 } else { # ebcdic(!) low = 0 high = 255 } for (i = low; i <= high; i++) { t = sprintf("%c", i) _ord_[t] = i } } d11230 3 a11232 10 Some explanation of the numbers used by `chr' is worthwhile. The most prominent character set in use today is ASCII. Although an 8-bit byte can hold 256 distinct values (from 0 to 255), ASCII only defines characters that use the values from 0 to 127.(1) In the now distant past, at least one minicomputer manufacturer used ASCII, but with mark parity, meaning that the leftmost bit in the byte is always 1. This means that on those systems, characters have numeric values from 128 to 255. Finally, large mainframe systems use the EBCDIC character set, which uses all 256 values. While there are other character sets in use on some older systems, they are not really worth worrying about: d11234 1 a11234 23 function ord(str, c) { # only first character is of interest c = substr(str, 1, 1) return _ord_[c] } function chr(c) { # force c to be numeric by adding 0 return sprintf("%c", c + 0) } #### test code #### # BEGIN \ # { # for (;;) { # printf("enter a character: ") # if (getline var <= 0) # break # printf("ord(%s) = %d\n", var, ord(var)) # } # } d11236 1 a11236 5 An obvious improvement to these functions is to move the code for the `_ord_init' function into the body of the `BEGIN' rule. It was written this way initially for ease of development. There is a "test program" in a `BEGIN' rule, to test the function. It is commented out for production use. d11238 5 a11242 1 ---------- Footnotes ---------- d11244 2 a11245 3 (1) ASCII has been extended in many countries to use the values from 128 to 255 for country-specific characters. If your system uses these extensions, you can simplify `_ord_init' to simply loop from 0 to 255. d11247 3 a11249 2  File: gawk.info, Node: Join Function, Next: Gettimeofday Function, Prev: Ordinal Functions, Up: General Functions d11251 2 a11252 2 Merging an Array into a String ------------------------------ d11254 8 a11261 4 When doing string processing, it is often useful to be able to join all the strings in an array into one long string. The following function, `join', accomplishes this task. It is used later in several of the application programs (*note Sample Programs::). d11263 12 a11274 9 Good function design is important; this function needs to be general but it should also have a reasonable default behavior. It is called with an array as well as the beginning and ending indices of the elements in the array to be merged. This assumes that the array indices are numeric--a reasonable assumption since the array was likely created with `split' (*note String Functions::): # join.awk --- join an array into a string function join(array, start, end, sep, result, i) d11276 5 a11280 8 if (sep == "") sep = " " else if (sep == SUBSEP) # magic value sep = "" result = array[start] for (i = start + 1; i <= end; i++) result = result sep array[i] return result d11283 2 a11284 8 An optional additional argument is the separator to use when joining the strings back together. If the caller supplies a nonempty value, `join' uses it; if it is not supplied, it has a null value. In this case, `join' uses a single blank as a default separator for the strings. If the value is equal to `SUBSEP', then `join' joins the strings with no separator between them. `SUBSEP' serves as a "magic" value to indicate that there should be no separation between the component strings.(1) d11286 8 a11293 1 ---------- Footnotes ---------- d11295 30 a11324 3 (1) It would be nice if `awk' had an assignment operator for concatenation. The lack of an explicit operator for concatenation makes string operations more difficult than they really need to be. d11326 7 a11332 2  File: gawk.info, Node: Gettimeofday Function, Prev: Join Function, Up: General Functions d11334 5 a11338 2 Managing the Time of Day ------------------------ d11340 2 a11341 11 The `systime' and `strftime' functions described in *Note Time Functions::, provide the minimum functionality necessary for dealing with the time of day in human readable form. While `strftime' is extensive, the control formats are not necessarily easy to remember or intuitively obvious when reading a program. The following function, `gettimeofday', populates a user-supplied array with preformatted time information. It returns a string with the current time formatted in the same way as the `date' utility: # gettimeofday.awk --- get the time of day in a usable format d11343 2 a11344 21 # Returns a string in the format of output of date(1) # Populates the array argument time with individual values: # time["second"] -- seconds (0 - 59) # time["minute"] -- minutes (0 - 59) # time["hour"] -- hours (0 - 23) # time["althour"] -- hours (0 - 12) # time["monthday"] -- day of month (1 - 31) # time["month"] -- month of year (1 - 12) # time["monthname"] -- name of the month # time["shortmonth"] -- short name of the month # time["year"] -- year modulo 100 (0 - 99) # time["fullyear"] -- full year # time["weekday"] -- day of week (Sunday = 0) # time["altweekday"] -- day of week (Monday = 0) # time["dayname"] -- name of weekday # time["shortdayname"] -- short name of weekday # time["yearday"] -- day of year (0 - 365) # time["timezone"] -- abbreviation of timezone name # time["ampm"] -- AM or PM designation # time["weeknum"] -- week number, Sunday first day # time["altweeknum"] -- week number, Monday first day d11346 4 a11349 4 function gettimeofday(time, ret, now, i) { # get time once, avoids unnecessary system calls now = systime() d11351 4 a11354 29 # return date(1)-style output ret = strftime("%a %b %d %H:%M:%S %Z %Y", now) # clear out target array delete time # fill in values, force numeric values to be # numeric by adding 0 time["second"] = strftime("%S", now) + 0 time["minute"] = strftime("%M", now) + 0 time["hour"] = strftime("%H", now) + 0 time["althour"] = strftime("%I", now) + 0 time["monthday"] = strftime("%d", now) + 0 time["month"] = strftime("%m", now) + 0 time["monthname"] = strftime("%B", now) time["shortmonth"] = strftime("%b", now) time["year"] = strftime("%y", now) + 0 time["fullyear"] = strftime("%Y", now) + 0 time["weekday"] = strftime("%w", now) + 0 time["altweekday"] = strftime("%u", now) + 0 time["dayname"] = strftime("%A", now) time["shortdayname"] = strftime("%a", now) time["yearday"] = strftime("%j", now) + 0 time["timezone"] = strftime("%Z", now) time["ampm"] = strftime("%p", now) time["weeknum"] = strftime("%U", now) + 0 time["altweeknum"] = strftime("%W", now) + 0 return ret d11357 8 a11364 5 The string indices are easier to use and read than the various formats required by `strftime'. The `alarm' program presented in *Note Alarm Program::, uses this function. A more general design for the `gettimeofday' function would have allowed the user to supply an optional timestamp value to use instead of the current time. d11366 19 a11384 2  File: gawk.info, Node: Data File Management, Next: Getopt Function, Prev: General Functions, Up: Library Functions d11386 4 a11389 2 Data File Management ==================== d11391 8 a11398 2 This minor node presents functions that are useful for managing command-line data files. d11400 2 a11401 1 * Menu: d11403 39 a11441 5 * Filetrans Function:: A function for handling data file transitions. * Rewind Function:: A function for rereading the current file. * File Checking:: Checking that data files are readable. * Empty Files:: Checking for zero-length files. * Ignoring Assigns:: Treating assignments as file names. d11443 13 a11455 2  File: gawk.info, Node: Filetrans Function, Next: Rewind Function, Up: Data File Management d11457 3 a11459 26 Noting Data File Boundaries --------------------------- The `BEGIN' and `END' rules are each executed exactly once at the beginning and end of your `awk' program, respectively (*note BEGIN/END::). We (the `gawk' authors) once had a user who mistakenly thought that the `BEGIN' rule is executed at the beginning of each data file and the `END' rule is executed at the end of each data file. When informed that this was not the case, the user requested that we add new special patterns to `gawk', named `BEGIN_FILE' and `END_FILE', that would have the desired behavior. He even supplied us the code to do so. Adding these special patterns to `gawk' wasn't necessary; the job can be done cleanly in `awk' itself, as illustrated by the following library program. It arranges to call two user-supplied functions, `beginfile' and `endfile', at the beginning and end of each data file. Besides solving the problem in only nine(!) lines of code, it does so _portably_; this works with any implementation of `awk': # transfile.awk # # Give the user a hook for filename transitions # # The user must supply functions beginfile() and endfile() # that each take the name of the file being started or # finished, respectively. d11461 8 a11468 6 FILENAME != _oldfilename \ { if (_oldfilename != "") endfile(_oldfilename) _oldfilename = FILENAME beginfile(FILENAME) a11469 2 END { endfile(FILENAME) } d11471 6 a11476 2 This file must be loaded before the user's "main" program, so that the rule it supplies is executed first. d11478 2 a11479 16 This rule relies on `awk''s `FILENAME' variable that automatically changes for each new data file. The current file name is saved in a private variable, `_oldfilename'. If `FILENAME' does not equal `_oldfilename', then a new data file is being processed and it is necessary to call `endfile' for the old file. Because `endfile' should only be called if a file has been processed, the program first checks to make sure that `_oldfilename' is not the null string. The program then assigns the current file name to `_oldfilename' and calls `beginfile' for the file. Because, like all `awk' variables, `_oldfilename' is initialized to the null string, this rule executes correctly even for the first data file. The program also supplies an `END' rule to do the final processing for the last file. Because this `END' rule comes before any `END' rules supplied in the "main" program, `endfile' is called first. Once again the value of multiple `BEGIN' and `END' rules should be clear. d11481 2 a11482 5 This version has same problem as the first version of `nextfile' (*note Nextfile Function::). If the same data file occurs twice in a row on the command line, then `endfile' and `beginfile' are not executed at the end of the first pass and at the beginning of the second pass. The following version solves the problem: d11484 4 a11487 11 # ftrans.awk --- handle data file transitions # # user supplies beginfile() and endfile() functions FNR == 1 { if (_filename_ != "") endfile(_filename_) _filename_ = FILENAME beginfile(FILENAME) } END { endfile(_filename_) } d11489 1 a11489 2 *Note Wc Program::, shows how this library function can be used and how it simplifies writing the main program. d11491 5 a11495 2  File: gawk.info, Node: Rewind Function, Next: File Checking, Prev: Filetrans Function, Up: Data File Management d11497 1 a11497 2 Rereading the Current File -------------------------- d11499 3 a11501 4 Another request for a new built-in function was for a `rewind' function that would make it possible to reread the current file. The requesting user didn't want to have to use `getline' (*note Getline::) inside a loop. d11503 3 a11505 4 However, as long as you are not in the `END' rule, it is quite easy to arrange to immediately close the current input file and then start over with it from the top. For lack of a better name, we'll call it `rewind': d11507 4 a11510 16 # rewind.awk --- rewind the current file and start over function rewind( i) { # shift remaining arguments up for (i = ARGC; i > ARGIND; i--) ARGV[i] = ARGV[i-1] # make sure gawk knows to keep going ARGC++ # make current file next to get done ARGV[ARGIND+1] = FILENAME # do it nextfile } d11512 2 a11513 4 This code relies on the `ARGIND' variable (*note Auto-set::), which is specific to `gawk'. If you are not using `gawk', you can use ideas presented in *Note Filetrans Function::, to either update `ARGIND' on your own or modify this code as appropriate. d11515 3 a11517 3 The `rewind' function also relies on the `nextfile' keyword (*note Nextfile Statement::). *Note Nextfile Function::, for a function version of `nextfile'. d11519 3 a11521 2  File: gawk.info, Node: File Checking, Next: Empty Files, Prev: Rewind Function, Up: Data File Management d11523 4 a11526 2 Checking for Readable Data Files -------------------------------- d11528 4 a11531 4 Normally, if you give `awk' a data file that isn't readable, it stops with a fatal error. There are times when you might want to just ignore such files and keep going. You can do this by prepending the following program to your `awk' program: d11533 12 a11544 1 # readable.awk --- library file to skip over unreadable files d11546 13 a11558 6 for (i = 1; i < ARGC; i++) { if (ARGV[i] ~ /^[A-Za-z_][A-Za-z0-9_]*=.*/ \ || ARGV[i] == "-") continue # assignment or standard input else if ((getline junk < ARGV[i]) < 0) # unreadable delete ARGV[i] d11560 1 a11560 1 close(ARGV[i]) a11561 1 } d11563 7 a11569 3 In `gawk', the `getline' won't be fatal (unless `--posix' is in force). Removing the element from `ARGV' with `delete' skips the file (since it's no longer in the list). d11571 3 a11573 2  File: gawk.info, Node: Empty Files, Next: Ignoring Assigns, Prev: File Checking, Up: Data File Management d11575 2 a11576 25 Checking For Zero-length Files ------------------------------ All known `awk' implementations silently skip over zero-length files. This is a by-product of `awk''s implicit read-a-record-and-match-against-the-rules loop: when `awk' tries to read a record from an empty file, it immediately receives an end of file indication, closes the file, and proceeds on to the next command-line data file, _without_ executing any user-level `awk' program code. Using `gawk''s `ARGIND' variable (*note Built-in Variables::), it is possible to detect when an empty data file has been skipped. Similar to the library file presented in *Note Filetrans Function::, the following library file calls a function named `zerofile' that the user must provide. The arguments passed are the file name and the position in `ARGV' where it was found: # zerofile.awk --- library file to process empty input files BEGIN { Argind = 0 } ARGIND > Argind + 1 { for (Argind++; Argind < ARGIND; Argind++) zerofile(ARGV[Argind], Argind) } d11578 7 a11584 1 ARGIND != Argind { Argind = ARGIND } d11586 2 a11587 4 END { if (ARGIND > Argind) for (Argind++; Argind <= ARGIND; Argind++) zerofile(ARGV[Argind], Argind) d11590 4 a11593 5 The user-level variable `Argind' allows the `awk' program to track its progress through `ARGV'. Whenever the program detects that `ARGIND' is greater than `Argind + 1', it means that one or more empty files were skipped. The action then calls `zerofile' for each such file, incrementing `Argind' along the way. d11595 4 a11598 2 The `Argind != ARGIND' rule simply keeps `Argind' up to date in the normal case. d11600 4 a11603 3 Finally, the `END' rule catches the case of any empty files at the end of the command-line arguments. Note that the test in the condition of the `for' loop uses the `<=' operator, not `<'. d11605 4 a11608 2 As an exercise, you might consider whether this same problem can be solved without relying on `gawk''s `ARGIND' variable. d11610 8 a11617 2 As a second exercise, revise this code to handle the case where an intervening value in `ARGV' is a variable assignment. d11619 7 a11625 23  File: gawk.info, Node: Ignoring Assigns, Prev: Empty Files, Up: Data File Management Treating Assignments as File Names ---------------------------------- Occasionally, you might not want `awk' to process command-line variable assignments (*note Assignment Options::). In particular, if you have file names that contain an `=' character, `awk' treats the file name as an assignment, and does not process it. Some users have suggested an additional command-line option for `gawk' to disable command-line assignments. However, some simple programming with a library file does the trick: # noassign.awk --- library file to avoid the need for a # special option that disables command-line assignments function disable_assigns(argc, argv, i) { for (i = 1; i < argc; i++) if (argv[i] ~ /^[A-Za-z_][A-Za-z_0-9]*=.*/) argv[i] = ("./" argv[i]) } d11627 1 a11627 3 BEGIN { if (No_command_assign) disable_assigns(ARGC, ARGV) d11630 15 a11644 1 You then run your program this way: d11646 2 a11647 1 awk -v No_command_assign=1 -f noassign.awk -f yourprog.awk * d11649 23 a11671 3 The function works by looping through the arguments. It prepends `./' to any argument that matches the form of a variable assignment, turning that argument into a file name. d11673 2 a11674 4 The use of `No_command_assign' allows you to disable command-line assignments at invocation time, by giving the variable a true value. When not set, it is initially zero (i.e., false), so the command-line arguments are left alone. d11676 6 a11681 2  File: gawk.info, Node: Getopt Function, Next: Passwd Functions, Prev: Data File Management, Up: Library Functions d11683 2 a11684 2 Processing Command-Line Options =============================== d11686 6 a11691 18 Most utilities on POSIX compatible systems take options, or "switches," on the command line that can be used to change the way a program behaves. `awk' is an example of such a program (*note Options::). Often, options take "arguments"; i.e., data that the program needs to correctly obey the command-line option. For example, `awk''s `-F' option requires a string to use as the field separator. The first occurrence on the command line of either `--' or a string that does not begin with `-' ends the options. Modern Unix systems provide a C function named `getopt' for processing command-line arguments. The programmer provides a string describing the one-letter options. If an option requires an argument, it is followed in the string with a colon. `getopt' is also passed the count and values of the command-line arguments and is called in a loop. `getopt' processes the command-line arguments for option letters. Each time around the loop, it returns a single character representing the next option letter that it finds, or `?' if it finds an invalid option. When it returns -1, there are no options left on the command line. d11693 2 a11694 4 When using `getopt', options that do not take arguments can be grouped together. Furthermore, options that take arguments require that the argument is present. The argument can immediately follow the option letter, or it can be a separate command-line argument. d11696 6 a11701 3 Given a hypothetical program that takes three command-line options, `-a', `-b', and `-c', where `-b' requires an argument, all of the following are valid ways of invoking the program: d11703 2 a11704 3 prog -a -b foo -c data1 data2 data3 prog -ac -bfoo -- data1 data2 data3 prog -acbfoo data1 data2 data3 d11706 2 a11707 5 Notice that when the argument is grouped with its option, the rest of the argument is considered to be the option's argument. In this example, `-acbfoo' indicates that all of the `-a', `-b', and `-c' options were supplied, and that `foo' is the argument to the `-b' option. d11709 5 a11713 2 `getopt' provides four external variables that the programmer can use: d11715 2 a11716 3 `optind' The index in the argument value array (`argv') where the first nonoption command-line argument can be found. d11718 4 a11721 2 `optarg' The string value of the argument to an option. d11723 4 a11726 4 `opterr' Usually `getopt' prints an error message when it finds an invalid option. Setting `opterr' to zero disables this feature. (An application might want to print its own error message.) d11728 4 a11731 2 `optopt' The letter representing the command-line option. d11733 4 a11736 2 The following C fragment shows how `getopt' might process command-line arguments for `awk': d11738 9 a11746 2 int main(int argc, char *argv[]) d11748 55 a11802 21 ... /* print our own message */ opterr = 0; while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) { switch (c) { case 'f': /* file */ ... break; case 'F': /* field separator */ ... break; case 'v': /* variable assignment */ ... break; case 'W': /* extension */ ... break; case '?': default: usage(); break; d11805 1 a11805 1 ... d11808 14 a11821 2 As a side point, `gawk' actually uses the GNU `getopt_long' function to process both normal and GNU-style long options (*note Options::). d11823 3 a11825 6 The abstraction provided by `getopt' is very useful and is quite handy in `awk' programs as well. Following is an `awk' version of `getopt'. This function highlights one of the greatest weaknesses in `awk', which is that it is very poor at manipulating single characters. Repeated calls to `substr' are necessary for accessing individual characters (*note String Functions::).(1) d11827 7 a11833 1 The discussion that follows walks through the code a bit at a time: d11835 3 a11837 6 # getopt.awk --- do C library getopt(3) function in awk # External variables: # Optind -- index in ARGV of first nonoption argument # Optarg -- string value of argument to current option # Opterr -- if nonzero, print our own diagnostic # Optopt -- current option letter d11839 1 a11839 4 # Returns: # -1 at end of options # ? for unrecognized option # a character representing the current option d11841 5 a11845 16 # Private Data: # _opti -- index in multi-flag option, e.g., -abc The function starts out with a list of the global variables it uses, what the return values are, what they mean, and any global variables that are "private" to this library function. Such documentation is essential for any program, and particularly for library functions. The `getopt' function first checks that it was indeed called with a string of options (the `options' parameter). If `options' has a zero length, `getopt' immediately returns -1: function getopt(argc, argv, options, thisopt, i) { if (length(options) == 0) # no options given return -1 d11847 12 a11858 7 if (argv[Optind] == "--") { # all done Optind++ _opti = 0 return -1 } else if (argv[Optind] !~ /^-[^: \t\n\f\r\v\b]/) { _opti = 0 return -1 d11860 4 d11865 7 a11871 5 The next thing to check for is the end of the options. A `--' ends the command-line options, as does any command-line argument that does not begin with a `-'. `Optind' is used to step through the array of command-line arguments; it retains its value across calls to `getopt', because it is a global variable. d11873 11 a11883 18 The regular expression that is used, `/^-[^: \t\n\f\r\v\b]/', is perhaps a bit of overkill; it checks for a `-' followed by anything that is not whitespace and not a colon. If the current command-line argument does not match this pattern, it is not an option, and it ends option processing: if (_opti == 0) _opti = 2 thisopt = substr(argv[Optind], _opti, 1) Optopt = thisopt i = index(options, thisopt) if (i == 0) { if (Opterr) printf("%c -- invalid option\n", thisopt) > "/dev/stderr" if (_opti >= length(argv[Optind])) { Optind++ _opti = 0 d11885 3 a11887 2 _opti++ return "?" d11889 1 a11889 51 The `_opti' variable tracks the position in the current command-line argument (`argv[Optind]'). If multiple options are grouped together with one `-' (e.g., `-abx'), it is necessary to return them to the user one at a time. If `_opti' is equal to zero, it is set to two, which is the index in the string of the next character to look at (we skip the `-', which is at position one). The variable `thisopt' holds the character, obtained with `substr'. It is saved in `Optopt' for the main program to use. If `thisopt' is not in the `options' string, then it is an invalid option. If `Opterr' is nonzero, `getopt' prints an error message on the standard error that is similar to the message from the C version of `getopt'. Because the option is invalid, it is necessary to skip it and move on to the next option character. If `_opti' is greater than or equal to the length of the current command-line argument, it is necessary to move on to the next argument, so `Optind' is incremented and `_opti' is reset to zero. Otherwise, `Optind' is left alone and `_opti' is merely incremented. In any case, because the option is invalid, `getopt' returns `?'. The main program can examine `Optopt' if it needs to know what the invalid option letter actually is. Continuing on: if (substr(options, i + 1, 1) == ":") { # get option argument if (length(substr(argv[Optind], _opti + 1)) > 0) Optarg = substr(argv[Optind], _opti + 1) else Optarg = argv[++Optind] _opti = 0 } else Optarg = "" If the option requires an argument, the option letter is followed by a colon in the `options' string. If there are remaining characters in the current command-line argument (`argv[Optind]'), then the rest of that string is assigned to `Optarg'. Otherwise, the next command-line argument is used (`-xFOO' versus `-x FOO'). In either case, `_opti' is reset to zero, because there are no more characters left to examine in the current command-line argument. Continuing: if (_opti == 0 || _opti >= length(argv[Optind])) { Optind++ _opti = 0 } else _opti++ return thisopt d11892 1 a11892 12 Finally, if `_opti' is either zero or greater than the length of the current command-line argument, it means this element in `argv' is through being processed, so `Optind' is incremented to point to the next element in `argv'. If neither condition is true, then only `_opti' is incremented, so that the next option letter can be processed on the next call to `getopt'. The `BEGIN' rule initializes both `Opterr' and `Optind' to one. `Opterr' is set to one, since the default behavior is for `getopt' to print a diagnostic message upon seeing an invalid option. `Optind' is set to one, since there's no reason to look at the program name, which is in `ARGV[0]': d11894 5 a11898 14 BEGIN { Opterr = 1 # default is to diagnose Optind = 1 # skip ARGV[0] # test program if (_getopt_test) { while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1) printf("c = <%c>, optarg = <%s>\n", _go_c, Optarg) printf("non-option arguments:\n") for (; Optind < ARGC; Optind++) printf("\tARGV[%d] = <%s>\n", Optind, ARGV[Optind]) } d11901 1 a11901 18 The rest of the `BEGIN' rule is a simple test program. Here is the result of two sample runs of the test program: $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x -| c = , optarg = <> -| c = , optarg = <> -| c = , optarg = -| non-option arguments: -| ARGV[3] = -| ARGV[4] = <-x> $ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc -| c = , optarg = <> error--> x -- invalid option -| c = , optarg = <> -| non-option arguments: -| ARGV[4] = -| ARGV[5] = d11903 2 a11904 4 In both runs, the first `--' terminates the arguments to `awk', so that it does not try to interpret the `-a', etc., as its own options. Several of the sample programs presented in *Note Sample Programs::, use `getopt' to process their arguments. d11906 2 a11907 1 ---------- Footnotes ---------- d11909 2 a11910 3 (1) This function was written before `gawk' acquired the ability to split strings into single characters using `""' as the separator. We have left it alone, since using `substr' is more portable. d11912 3 a11914 2  File: gawk.info, Node: Passwd Functions, Next: Group Functions, Prev: Getopt Function, Up: Library Functions d11916 1 a11916 2 Reading the User Database ========================= d11918 2 a11919 9 The `PROCINFO' array (*note Built-in Variables::) provides access to the current user's real and effective user and group ID numbers, and if available, the user's supplementary group set. However, because these are numbers, they do not provide very useful information to the average user. There needs to be some way to find the user information associated with the user and group ID numbers. This minor node presents a suite of functions for retrieving information from the user database. *Note Group Functions::, for a similar suite that retrieves information from the group database. d11921 4 a11924 6 The POSIX standard does not define the file where user information is kept. Instead, it provides the `' header file and several C language subroutines for obtaining user information. The primary function is `getpwent', for "get password entry." The "password" comes from the original user database file, `/etc/passwd', which stores user information, along with the encrypted passwords (hence the name). d11926 5 a11930 10 While an `awk' program could simply read `/etc/passwd' directly, this file may not contain complete information about the system's set of users.(1) To be sure you are able to produce a readable and complete version of the user database, it is necessary to write a small C program that calls `getpwent'. `getpwent' is defined as returning a pointer to a `struct passwd'. Each time it is called, it returns the next entry in the database. When there are no more entries, it returns `NULL', the null pointer. When this happens, the C program should call `endpwent' to close the database. Following is `pwcat', a C program that "cats" the password database: d11932 4 a11935 7 /* * pwcat.c * * Generate a printable version of the password database */ #include #include d11937 1 a11937 4 int main(argc, argv) int argc; char **argv; d11939 2 a11940 1 struct passwd *p; d11942 12 a11953 7 while ((p = getpwent()) != NULL) printf("%s:%s:%ld:%ld:%s:%s:%s\n", p->pw_name, p->pw_passwd, (long) p->pw_uid, (long) p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell); endpwent(); return 0; d11956 4 a11959 32 If you don't understand C, don't worry about it. The output from `pwcat' is the user database, in the traditional `/etc/passwd' format of colon-separated fields. The fields are: Login name The user's login name. Encrypted password The user's encrypted password. This may not be available on some systems. User-ID The user's numeric user ID number. Group-ID The user's numeric group ID number. Full name The user's full name, and perhaps other information associated with the user. Home directory The user's login (or "home") directory (familiar to shell programmers as `$HOME'). Login shell The program that is run when the user logs in. This is usually a shell, such as `bash'. A few lines representative of `pwcat''s output are as follows: $ pwcat -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh -| nobody:*:65534:65534::/: -| daemon:*:1:1::/: -| sys:*:2:2::/:/bin/csh -| bin:*:3:3::/bin: -| arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh -| miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh -| andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh ... With that introduction, following is a group of functions for getting user information. There are several functions here, corresponding to the C functions of the same names: a11960 7 # passwd.awk --- access password file information BEGIN { # tailor this to suit your system _pw_awklib = "/usr/local/libexec/awk/" } function _pw_init( oldfs, oldrs, olddol0, pwcat, using_fw) d11962 8 a11969 24 if (_pw_inited) return oldfs = FS oldrs = RS olddol0 = $0 using_fw = (PROCINFO["FS"] == "FIELDWIDTHS") FS = ":" RS = "\n" pwcat = _pw_awklib "pwcat" while ((pwcat | getline) > 0) { _pw_byname[$1] = $0 _pw_byuid[$3] = $0 _pw_bycount[++_pw_total] = $0 } close(pwcat) _pw_count = 0 _pw_inited = 1 FS = oldfs if (using_fw) FIELDWIDTHS = FIELDWIDTHS RS = oldrs $0 = olddol0 d11972 1 a11972 4 The `BEGIN' rule sets a private variable to the directory where `pwcat' is stored. Because it is used to help out an `awk' library routine, we have chosen to put it in `/usr/local/libexec/awk'; however, you might want it to be in a different directory on your system. d11974 5 a11978 18 The function `_pw_init' keeps three copies of the user information in three associative arrays. The arrays are indexed by username (`_pw_byname'), by user ID number (`_pw_byuid'), and by order of occurrence (`_pw_bycount'). The variable `_pw_inited' is used for efficiency; `_pw_init' needs only to be called once. Because this function uses `getline' to read information from `pwcat', it first saves the values of `FS', `RS', and `$0'. It notes in the variable `using_fw' whether field splitting with `FIELDWIDTHS' is in effect or not. Doing so is necessary, since these functions could be called from anywhere within a user's program, and the user may have his or her own way of splitting records and fields. The `using_fw' variable checks `PROCINFO["FS"]', which is `"FIELDWIDTHS"' if field splitting is being done with `FIELDWIDTHS'. This makes it possible to restore the correct field-splitting mechanism later. The test can only be true for `gawk'. It is false if using `FS' or on some other `awk' implementation. d11980 6 a11985 6 The main part of the function uses a loop to read database lines, split the line into fields, and then store the line into each array as necessary. When the loop is done, `_pw_init' cleans up by closing the pipeline, setting `_pw_inited' to one, and restoring `FS' (and `FIELDWIDTHS' if necessary), `RS', and `$0'. The use of `_pw_count' is explained shortly. d11987 1 a11987 3 The `getpwnam' function takes a username as a string argument. If that user is in the database, it returns the appropriate line. Otherwise, it returns the null string: d11989 1 a11989 1 function getpwnam(name) d11991 2 a11992 4 _pw_init() if (name in _pw_byname) return _pw_byname[name] return "" d11995 5 a11999 3 Similarly, the `getpwuid' function takes a user ID number argument. If that user number is in the database, it returns the appropriate line. Otherwise, it returns the null string: d12001 4 a12004 7 function getpwuid(uid) { _pw_init() if (uid in _pw_byuid) return _pw_byuid[uid] return "" } d12006 1 a12006 3 The `getpwent' function simply steps through the database, one entry at a time. It uses `_pw_count' to track its current position in the `_pw_bycount' array: d12008 1 a12008 7 function getpwent() { _pw_init() if (_pw_count < _pw_total) return _pw_bycount[++_pw_count] return "" } d12010 2 a12011 2 The `endpwent' function resets `_pw_count' to zero, so that subsequent calls to `getpwent' start over again: d12013 2 a12014 4 function endpwent() { _pw_count = 0 } d12016 3 a12018 10 A conscious design decision in this suite was made that each subroutine calls `_pw_init' to initialize the database arrays. The overhead of running a separate process to generate the user database, and the I/O to scan it, are only incurred if the user's main program actually calls one of these functions. If this library file is loaded along with a user's program, but none of the routines are ever called, then there is no extra runtime overhead. (The alternative is move the body of `_pw_init' into a `BEGIN' rule, which always runs `pwcat'. This simplifies the code but runs an extra process that may never be needed.) d12020 4 a12023 7 In turn, calling `_pw_init' is not too expensive, because the `_pw_inited' variable keeps the program from reading the data more than once. If you are worried about squeezing every last cycle out of your `awk' program, the check of `_pw_inited' could be moved out of `_pw_init' and duplicated in all the other functions. In practice, this is not necessary, since most `awk' programs are I/O-bound, and it clutters up the code. d12025 3 a12027 1 The `id' program in *Note Id Program::, uses these functions. d12029 3 a12031 1 ---------- Footnotes ---------- d12033 3 a12035 2 (1) It is often the case that password information is stored in a network database. d12037 2 a12038 2  File: gawk.info, Node: Group Functions, Prev: Passwd Functions, Up: Library Functions d12040 4 a12043 2 Reading the Group Database ========================== d12045 2 a12046 8 Much of the discussion presented in *Note Passwd Functions::, applies to the group database as well. Although there has traditionally been a well-known file (`/etc/group') in a well-known format, the POSIX standard only provides a set of C library routines (`' and `getgrent') for accessing the information. Even though this file may exist, it likely does not have complete information. Therefore, as with the user database, it is necessary to have a small C program that generates the group database as its output. d12048 14 a12061 1 `grcat', a C program that "cats" the group database, is as follows: d12063 16 a12078 7 /* * grcat.c * * Generate a printable version of the group database */ #include #include d12080 1 a12080 4 int main(argc, argv) int argc; char **argv; d12082 33 a12114 2 struct group *g; int i; d12116 3 a12118 9 while ((g = getgrent()) != NULL) { printf("%s:%s:%ld:", g->gr_name, g->gr_passwd, (long) g->gr_gid); for (i = 0; g->gr_mem[i] != NULL; i++) { printf("%s", g->gr_mem[i]); if (g->gr_mem[i+1] != NULL) putchar(','); } putchar('\n'); a12119 2 endgrent(); return 0; d12122 18 a12139 2 Each line in the group database represents one group. The fields are separated with colons and represent the following information: d12141 21 a12161 14 Group name The group's name. Group password The group's encrypted password. In practice, this field is never used; it is usually empty or set to `*'. Group-ID The group's numeric group ID number; this number should be unique within the file. Group member list A comma-separated list of usernames. These users are members of the group. Modern Unix systems allow users to be members of several groups simultaneously. If your system does, then there are elements `"group1"' through `"groupN"' in `PROCINFO' for those group ID numbers. (Note that `PROCINFO' is a `gawk' extension; *note Built-in Variables::.) d12163 4 a12166 1 Here is what running `grcat' might produce: d12168 11 a12178 8 $ grcat -| wheel:*:0:arnold -| nogroup:*:65534: -| daemon:*:1: -| kmem:*:2: -| staff:*:10:arnold,miriam,andy -| other:*:20: ... d12180 2 a12181 3 Here are the functions for obtaining information from the group database. There are several, modeled after the C library functions of the same names: d12183 3 a12185 5 # group.awk --- functions for dealing with the group file BEGIN \ { # Change to suit your system _gr_awklib = "/usr/local/libexec/awk/" a12187 2 function _gr_init( oldfs, oldrs, olddol0, grcat, using_fw, n, a, i) d12189 1 a12189 2 if (_gr_inited) return d12191 10 a12200 6 oldfs = FS oldrs = RS olddol0 = $0 using_fw = (PROCINFO["FS"] == "FIELDWIDTHS") FS = ":" RS = "\n" d12202 10 a12211 18 grcat = _gr_awklib "grcat" while ((grcat | getline) > 0) { if ($1 in _gr_byname) _gr_byname[$1] = _gr_byname[$1] "," $4 else _gr_byname[$1] = $0 if ($3 in _gr_bygid) _gr_bygid[$3] = _gr_bygid[$3] "," $4 else _gr_bygid[$3] = $0 n = split($4, a, "[ \t]*,[ \t]*") for (i = 1; i <= n; i++) if (a[i] in _gr_groupsbyuser) _gr_groupsbyuser[a[i]] = \ _gr_groupsbyuser[a[i]] " " $1 else _gr_groupsbyuser[a[i]] = $1 d12213 6 a12218 10 _gr_bycount[++_gr_count] = $0 } close(grcat) _gr_count = 0 _gr_inited++ FS = oldfs if (using_fw) FIELDWIDTHS = FIELDWIDTHS RS = oldrs $0 = olddol0 d12221 5 a12225 4 The `BEGIN' rule sets a private variable to the directory where `grcat' is stored. Because it is used to help out an `awk' library routine, we have chosen to put it in `/usr/local/libexec/awk'. You might want it to be in a different directory on your system. d12227 2 a12228 6 These routines follow the same general outline as the user database routines (*note Passwd Functions::). The `_gr_inited' variable is used to ensure that the database is scanned no more than once. The `_gr_init' function first saves `FS', `FIELDWIDTHS', `RS', and `$0', and then sets `FS' and `RS' to the correct values for scanning the group information. d12230 1 a12230 5 The group information is stored is several associative arrays. The arrays are indexed by group name (`_gr_byname'), by group ID number (`_gr_bygid'), and by position in the database (`_gr_bycount'). There is an additional array indexed by username (`_gr_groupsbyuser'), which is a space-separated list of groups to which each user belongs. d12232 3 a12234 4 Unlike the user database, it is possible to have multiple records in the database for the same group. This is common when a group has a large number of members. A pair of such entries might look like the following: d12236 2 a12237 2 tvpeople:*:101:johnny,jay,arsenio tvpeople:*:101:david,conan,tom,joan d12239 5 a12243 10 For this reason, `_gr_init' looks to see if a group name or group ID number is already seen. If it is, then the usernames are simply concatenated onto the previous list of users. (There is actually a subtle problem with the code just presented. Suppose that the first time there were no names. This code adds the names with a leading comma. It also doesn't check that there is a `$4'.) Finally, `_gr_init' closes the pipeline to `grcat', restores `FS' (and `FIELDWIDTHS' if necessary), `RS', and `$0', initializes `_gr_count' to zero (it is used later), and makes `_gr_inited' nonzero. d12245 2 a12246 3 The `getgrnam' function takes a group name as its argument, and if that group exists, it is returned. Otherwise, `getgrnam' returns the null string: d12248 14 a12261 7 function getgrnam(group) { _gr_init() if (group in _gr_byname) return _gr_byname[group] return "" } d12263 3 a12265 2 The `getgrgid' function is similar, it takes a numeric group ID and looks up the information associated with that group ID: d12267 30 a12296 6 function getgrgid(gid) { _gr_init() if (gid in _gr_bygid) return _gr_bygid[gid] return "" d12299 8 a12306 2 The `getgruser' function does not have a C counterpart. It takes a username and returns the list of groups that have the user as a member: d12308 1 a12308 1 function getgruser(user) d12310 2 a12311 4 _gr_init() if (user in _gr_groupsbyuser) return _gr_groupsbyuser[user] return "" d12313 2 a12314 5 The `getgrent' function steps through the database one entry at a time. It uses `_gr_count' to track its position in the list: function getgrent() d12316 10 a12325 4 _gr_init() if (++_gr_count in _gr_bycount) return _gr_bycount[_gr_count] return "" d12328 8 a12335 2 The `endgrent' function resets `_gr_count' to zero so that `getgrent' can start over again: d12337 1 a12337 1 function endgrent() d12339 15 a12353 1 _gr_count = 0 d12356 1 a12356 4 As with the user database routines, each function calls `_gr_init' to initialize the arrays. Doing so only incurs the extra overhead of running `grcat' if these functions are used (as opposed to moving the body of `_gr_init' into a `BEGIN' rule). d12358 3 a12360 5 Most of the work is in scanning the database and building the various associative arrays. The functions that the user calls are themselves very simple, relying on `awk''s associative arrays to do work. The `id' program in *Note Id Program::, uses these functions. d12363 1 a12363 1 File: gawk.info, Node: Sample Programs, Next: Language History, Prev: Library Functions, Up: Top d12365 2 a12366 2 Practical `awk' Programs ************************ d12368 2 a12369 7 *Note Library Functions::, presents the idea that reading programs in a language contributes to learning that language. This major node continues that theme, presenting a potpourri of `awk' programs for your reading enjoyment. Many of these programs use the library functions presented in *Note Library Functions::. d12373 11 a12383 3 * Running Examples:: How to run these examples. * Clones:: Clones of common utilities. * Miscellaneous Programs:: Some interesting `awk' programs. d12386 1 a12386 1 File: gawk.info, Node: Running Examples, Next: Clones, Up: Sample Programs d12388 2 a12389 2 Running the Example Programs ============================ d12391 5 a12395 1 To run a given program, you would typically do something like this: d12397 4 a12400 1 awk -f PROGRAM -- OPTIONS FILES d12402 23 a12424 3 Here, PROGRAM is the name of the `awk' program (such as `cut.awk'), OPTIONS are any command-line options for the program that start with a `-', and FILES are the actual data files. d12426 2 a12427 2 If your system supports the `#!' executable interpreter mechanism (*note Executable Scripts::), you can instead run your program directly: d12429 2 a12430 1 cut.awk -c1-8 myfiles > results d12432 5 a12436 1 If your `awk' is not `gawk', you may instead need to use this: d12438 2 a12439 1 cut.awk -- -c1-8 myfiles > results d12441 48 a12488 2  File: gawk.info, Node: Clones, Next: Miscellaneous Programs, Prev: Running Examples, Up: Sample Programs d12490 5 a12494 2 Reinventing Wheels for Fun and Profit ===================================== d12496 27 a12522 10 This minor node presents a number of POSIX utilities that are implemented in `awk'. Reinventing these programs in `awk' is often enjoyable, because the algorithms can be very clearly expressed, and the code is usually very concise and simple. This is true because `awk' does so much for you. It should be noted that these programs are not necessarily intended to replace the installed versions on your system. Instead, their purpose is to illustrate `awk' language programming for "real world" tasks. d12524 7 a12530 1 The programs are presented in alphabetical order. d12532 15 a12546 1 * Menu: d12548 2 a12549 7 * Cut Program:: The `cut' utility. * Egrep Program:: The `egrep' utility. * Id Program:: The `id' utility. * Split Program:: The `split' utility. * Tee Program:: The `tee' utility. * Uniq Program:: The `uniq' utility. * Wc Program:: The `wc' utility. d12551 2 a12552 2  File: gawk.info, Node: Cut Program, Next: Egrep Program, Up: Clones d12554 3 a12556 2 Cutting out Fields and Columns ------------------------------ d12558 1 a12558 5 The `cut' utility selects, or "cuts," characters or fields from its standard input and sends them to its standard output. Fields are separated by tabs by default, but you may supply a command-line option to change the field "delimiter" (i.e., the field-separator character). `cut''s definition of fields is less general than `awk''s. d12560 15 a12574 3 A common use of `cut' might be to pull out just the login name of logged-on users from the output of `who'. For example, the following pipeline generates a sorted, unique list of the logged-on users: d12576 5 a12580 1 who | cut -c1-8 | sort | uniq d12582 2 a12583 1 The options for `cut' are: d12585 2 a12586 5 `-c LIST' Use LIST as the list of characters to cut out. Items within the list may be separated by commas, and ranges of characters can be separated with dashes. The list `1-8,15,22-35' specifies characters 1 through 8, 15, and 22 through 35. d12588 2 a12589 2 `-f LIST' Use LIST as the list of fields to cut out. d12591 2 a12592 3 `-d DELIM' Use DELIM as the field-separator character instead of the tab character. d12594 5 a12598 2 `-s' Suppress printing of lines that do not contain the field delimiter. d12600 4 a12603 3 The `awk' implementation of `cut' uses the `getopt' library function (*note Getopt Function::) and the `join' library function (*note Join Function::). d12605 2 a12606 3 The program begins with a comment describing the options, the library functions needed, and a `usage' function that prints out a usage message and exits. `usage' is called if invalid arguments are supplied: d12608 41 a12648 9 # cut.awk --- implement cut in awk # Options: # -f list Cut fields # -d c Field delimiter character # -c list Cut characters # # -s Suppress lines without the delimiter # # Requires getopt and join library functions a12649 1 function usage( e1, e2) d12651 2 a12652 5 e1 = "usage: cut [-f list] [-d c] [-s] [files...]" e2 = "usage: cut [-c list] [files...]" print e1 > "/dev/stderr" print e2 > "/dev/stderr" exit 1 d12655 15 a12669 2 The variables `e1' and `e2' are used so that the function fits nicely on the screen. d12671 2 a12672 8 Next comes a `BEGIN' rule that parses the command-line options. It sets `FS' to a single TAB character, because that is `cut''s default field separator. The output field separator is also set to be the same as the input field separator. Then `getopt' is used to step through the command-line options. Exactly one of the variables `by_fields' or `by_chars' is set to true, to indicate that processing should be done by fields or by characters, respectively. When cutting by characters, the output field separator is set to the null string: d12674 3 a12676 30 BEGIN \ { FS = "\t" # default OFS = FS while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) { if (c == "f") { by_fields = 1 fieldlist = Optarg } else if (c == "c") { by_chars = 1 fieldlist = Optarg OFS = "" } else if (c == "d") { if (length(Optarg) > 1) { printf("Using first character of %s" \ " for delimiter\n", Optarg) > "/dev/stderr" Optarg = substr(Optarg, 1, 1) } FS = Optarg OFS = FS if (FS == " ") # defeat awk semantics FS = "[ ]" } else if (c == "s") suppress++ else usage() } for (i = 1; i < Optind; i++) ARGV[i] = "" d12678 2 a12679 7 Special care is taken when the field delimiter is a space. Using a single space (`" "') for the value of `FS' is incorrect--`awk' would separate fields with runs of spaces, tabs, and/or newlines, and we want them to be separated with individual spaces. Also, note that after `getopt' is through, we have to clear out all the elements of `ARGV' from 1 to `Optind', so that `awk' does not try to process the command-line options as file names. d12681 2 a12682 5 After dealing with the command-line options, the program verifies that the options make sense. Only one or the other of `-c' and `-f' should be used, and both require a field list. Then the program calls either `set_fieldlist' or `set_charlist' to pull apart the list of fields or characters: d12684 5 a12688 16 if (by_fields && by_chars) usage() if (by_fields == 0 && by_chars == 0) by_fields = 1 # default if (fieldlist == "") { print "cut: needs list for -c or -f" > "/dev/stderr" exit 1 } if (by_fields) set_fieldlist() else set_charlist() } d12690 4 a12693 7 `set_fieldlist' is used to split the field list apart at the commas and into an array. Then, for each element of the array, it looks to see if it is actually a range, and if so, splits it apart. The range is verified to make sure the first number is smaller than the second. Each number in the list is added to the `flist' array, which simply lists the fields that will be printed. Normal field splitting is used. The program lets `awk' handle the job of doing the field splitting: d12695 4 a12698 19 function set_fieldlist( n, m, i, j, k, f, g) { n = split(fieldlist, f, ",") j = 1 # index in flist for (i = 1; i <= n; i++) { if (index(f[i], "-") != 0) { # a range m = split(f[i], g, "-") if (m != 2 || g[1] >= g[2]) { printf("bad field list: %s\n", f[i]) > "/dev/stderr" exit 1 } for (k = g[1]; k <= g[2]; k++) flist[j++] = k } else flist[j++] = f[i] } nfields = j - 1 } d12700 9 a12708 4 The `set_charlist' function is more complicated than `set_fieldlist'. The idea here is to use `gawk''s `FIELDWIDTHS' variable (*note Constant Size::), which describes constant-width input. When using a character list, that is exactly what we have. d12710 5 a12714 10 Setting up `FIELDWIDTHS' is more complicated than simply listing the fields that need to be printed. We have to keep track of the fields to print and also the intervening characters that have to be skipped. For example, suppose you wanted characters 1 through 8, 15, and 22 through 35. You would use `-c 1-8,15,22-35'. The necessary value for `FIELDWIDTHS' is `"8 6 1 6 14"'. This yields five fields, and the fields to print are `$1', `$3', and `$5'. The intermediate fields are "filler", which is stuff in between the desired data. `flist' lists the fields to print, and `t' tracks the complete field list, including filler fields: d12716 5 a12720 39 function set_charlist( field, i, j, f, g, t, filler, last, len) { field = 1 # count total fields n = split(fieldlist, f, ",") j = 1 # index in flist for (i = 1; i <= n; i++) { if (index(f[i], "-") != 0) { # range m = split(f[i], g, "-") if (m != 2 || g[1] >= g[2]) { printf("bad character list: %s\n", f[i]) > "/dev/stderr" exit 1 } len = g[2] - g[1] + 1 if (g[1] > 1) # compute length of filler filler = g[1] - last - 1 else filler = 0 if (filler) t[field++] = filler t[field++] = len # length of field last = g[2] flist[j++] = field - 1 } else { if (f[i] > 1) filler = f[i] - last - 1 else filler = 0 if (filler) t[field++] = filler t[field++] = 1 last = f[i] flist[j++] = field - 1 } } FIELDWIDTHS = join(t, 1, field - 1) nfields = j - 1 } d12722 2 a12723 12 Next is the rule that actually processes the data. If the `-s' option is given, then `suppress' is true. The first `if' statement makes sure that the input record does have the field separator. If `cut' is processing fields, `suppress' is true, and the field separator character is not in the record, then the record is skipped. If the record is valid, then `gawk' has split the data into fields, either using the character in `FS' or using fixed-length fields and `FIELDWIDTHS'. The loop goes through the list of fields that should be printed. The corresponding field is printed if it contains data. If the next field also has data, then the separator character is written out between the fields: d12725 11 d12737 4 a12740 2 if (by_fields && suppress && index($0, FS) != 0) next d12742 7 a12748 5 for (i = 1; i <= nfields; i++) { if ($flist[i] != "") { printf "%s", $flist[i] if (i < nfields && $flist[i+1] != "") printf "%s", OFS d12750 15 d12766 11 a12776 1 print "" d12779 4 a12782 5 This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to do the character-based cutting. While it is possible in other `awk' implementations to use `substr' (*note String Functions::), it is also extremely painful. The `FIELDWIDTHS' variable supplies an elegant solution to the problem of picking the input line apart by characters. d12785 24 a12808 1 File: gawk.info, Node: Egrep Program, Next: Id Program, Prev: Cut Program, Up: Clones d12810 6 a12815 2 Searching for Regular Expressions in Files ------------------------------------------ d12817 2 a12818 3 The `egrep' utility searches files for patterns. It uses regular expressions that are almost identical to those available in `awk' (*note Regexp::). It is used in the following manner: d12820 3 a12822 1 egrep [ OPTIONS ] 'PATTERN' FILES ... d12824 2 a12825 6 The PATTERN is a regular expression. In typical usage, the regular expression is quoted to prevent the shell from expanding any of the special characters as file name wildcards. Normally, `egrep' prints the lines that matched. If multiple file names are provided on the command line, each output line is preceded by the name of the file and a colon. d12827 4 a12830 1 The options to `egrep' are as follows: d12832 5 a12836 3 `-c' Print out a count of the lines that matched the pattern, instead of the lines themselves. d12838 3 a12840 3 `-s' Be silent. No output is produced and the exit value indicates whether the pattern was matched. d12842 5 a12846 4 `-v' Invert the sense of the test. `egrep' prints the lines that do _not_ match the pattern and exits successfully if the pattern is not matched. d12848 12 a12859 2 `-i' Ignore case distinctions in both the pattern and the input data. d12861 2 a12862 3 `-l' Only print (list) the names of the files that matched, not the lines that matched. d12864 1 a12864 3 `-e PATTERN' Use PATTERN as the regexp to match. The purpose of the `-e' option is to allow patterns that start with a `-'. d12866 2 a12867 3 This version uses the `getopt' library function (*note Getopt Function::) and the file transition library program (*note Filetrans Function::). d12869 2 a12870 4 The program begins with a descriptive comment and then a `BEGIN' rule that processes the command-line arguments with `getopt'. The `-i' (ignore case) option is particularly easy with `gawk'; we just use the `IGNORECASE' built-in variable (*note Built-in Variables::): d12872 6 a12877 28 # egrep.awk --- simulate egrep in awk # Options: # -c count of lines # -s silent - use exit value # -v invert test, success if no match # -i ignore case # -l print filenames only # -e argument is pattern # # Requires getopt and file transition library functions BEGIN { while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) { if (c == "c") count_only++ else if (c == "s") no_print++ else if (c == "v") invert++ else if (c == "i") IGNORECASE = 1 else if (c == "l") filenames_only++ else if (c == "e") pattern = Optarg else usage() } d12879 2 a12880 7 Next comes the code that handles the `egrep'-specific behavior. If no pattern is supplied with `-e', the first nonoption on the command line is used. The `awk' command-line arguments up to `ARGV[Optind]' are cleared, so that `awk' won't try to process them as files. If no files are specified, the standard input is used, and if multiple files are specified, we make sure to note this so that the file names can precede the matched lines in the output: d12882 5 a12886 13 if (pattern == "") pattern = ARGV[Optind++] for (i = 1; i < Optind; i++) ARGV[i] = "" if (Optind >= ARGC) { ARGV[1] = "-" ARGC = 2 } else if (ARGC - Optind > 1) do_filenames++ # if (IGNORECASE) # pattern = tolower(pattern) d12889 2 a12890 3 The last two lines are commented out, since they are not needed in `gawk'. They should be uncommented if you have to use another version of `awk'. d12892 2 a12893 4 The next set of lines should be uncommented if you are not using `gawk'. This rule translates all the characters in the input line into lowercase if the `-i' option is specified.(1) The rule is commented out since it is not necessary with `gawk': d12895 2 a12896 4 #{ # if (IGNORECASE) # $0 = tolower($0) #} d12898 2 a12899 6 The `beginfile' function is called by the rule in `ftrans.awk' when each new file is processed. In this case, it is very simple; all it does is initialize a variable `fcount' to zero. `fcount' tracks how many lines in the current file matched the pattern (naming the parameter `junk' shows we know that `beginfile' is called with a parameter, but that we're not interested in its value): d12901 2 a12902 4 function beginfile(junk) { fcount = 0 } d12904 7 a12910 8 The `endfile' function is called after each file has been processed. It affects the output only when the user wants a count of the number of lines that matched. `no_print' is true only if the exit status is desired. `count_only' is true if line counts are desired. `egrep' therefore only prints line counts if printing and counting are enabled. The output format must be adjusted depending upon the number of files to process. Finally, `fcount' is added to `total', so that we know the total number of lines that matched the pattern: d12912 3 a12914 10 function endfile(file) { if (! no_print && count_only) if (do_filenames) print file ":" fcount else print fcount total += fcount } d12916 5 a12920 15 The following rule does most of the work of matching lines. The variable `matches' is true if the line matched the pattern. If the user wants lines that did not match, the sense of `matches' is inverted using the `!' operator. `fcount' is incremented with the value of `matches', which is either one or zero, depending upon a successful or unsuccessful match. If the line does not match, the `next' statement just moves on to the next record. A number of additional tests are made, but they are only done if we are not counting lines. First, if the user only wants exit status (`no_print' is true), then it is enough to know that _one_ line in this file matched, and we can skip on to the next file with `nextfile'. Similarly, if we are only printing file names, we can print the file name, and then skip to the next file with `nextfile'. Finally, each line is printed, with a leading file name and colon if necessary: d12922 5 d12928 3 a12930 3 matches = ($0 ~ pattern) if (invert) matches = ! matches d12932 3 a12934 19 fcount += matches # 1 or 0 if (! matches) next if (! count_only) { if (no_print) nextfile if (filenames_only) { print FILENAME nextfile } if (do_filenames) print FILENAME ":" $0 else print } d12937 3 a12939 2 The `END' rule takes care of producing the correct exit status. If there are no matches, the exit status is one; otherwise it is zero: d12941 1 a12941 6 END \ { if (total == 0) exit 1 exit 0 } d12943 2 a12944 2 The `usage' function prints a usage message in case of invalid options, and then exits: d12946 2 a12947 7 function usage( e) { e = "Usage: egrep [-csvil] [-e pat] [files ...]" e = e "\n\tegrep [-csvil] pat [files ...]" print e > "/dev/stderr" exit 1 } d12949 2 a12950 2 The variable `e' is used so that the function fits nicely on the printed page. d12952 6 a12957 6 Just a note on programming style: you may have noticed that the `END' rule uses backslash continuation, with the open brace on a line by itself. This is so that it more closely resembles the way functions are written. Many of the examples in this major node use this style. You can decide for yourself if you like writing your `BEGIN' and `END' rules this way or not. d12959 4 a12962 1 ---------- Footnotes ---------- d12964 2 a12965 5 (1) It also introduces a subtle bug; if a match happens, we output the translated line, not the original.  File: gawk.info, Node: Id Program, Next: Split Program, Prev: Egrep Program, Up: Clones d12967 3 a12969 2 Printing out User Information ----------------------------- d12971 3 a12973 5 The `id' utility lists a user's real and effective user ID numbers, real and effective group ID numbers, and the user's group set, if any. `id' only prints the effective user ID and group ID if they are different from the real ones. If possible, `id' also supplies the corresponding user and group names. The output might look like this: d12975 3 a12977 2 $ id -| uid=2076(arnold) gid=10(staff) groups=10(staff),4(tty) d12979 17 a12995 3 This information is part of what is provided by `gawk''s `PROCINFO' array (*note Built-in Variables::). However, the `id' utility provides a more palatable output than just individual numbers. d12997 2 a12998 3 Here is a simple version of `id' written in `awk'. It uses the user database library functions (*note Passwd Functions::) and the group database library functions (*note Group Functions::): d13000 3 a13002 6 The program is fairly straightforward. All the work is done in the `BEGIN' rule. The user and group ID numbers are obtained from `PROCINFO'. The code is repetitive. The entry in the user database for the real user ID number is split into parts at the `:'. The name is the first field. Similar code is used for the effective user ID number and the group numbers: d13004 6 a13009 6 # id.awk --- implement id in awk # # Requires user and group library functions # output is: # uid=12(foo) euid=34(bar) gid=3(baz) \ # egid=5(blat) groups=9(nine),2(two),1(one) d13011 1 a13011 1 BEGIN \ d13013 5 a13017 10 uid = PROCINFO["uid"] euid = PROCINFO["euid"] gid = PROCINFO["gid"] egid = PROCINFO["egid"] printf("uid=%d", uid) pw = getpwuid(uid) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) d13019 7 a13025 38 if (euid != uid) { printf(" euid=%d", euid) pw = getpwuid(euid) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } } printf(" gid=%d", gid) pw = getgrgid(gid) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } if (egid != gid) { printf(" egid=%d", egid) pw = getgrgid(egid) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } } for (i = 1; ("group" i) in PROCINFO; i++) { if (i == 1) printf(" groups=") group = PROCINFO["group" i] printf("%d", group) pw = getgrgid(group) if (pw != "") { split(pw, a, ":") printf("(%s)", a[1]) } if (("group" (i+1)) in PROCINFO) printf(",") a13026 2 print "" d13029 1 a13029 13 The test in the `for' loop is worth noting. Any supplementary groups in the `PROCINFO' array have the indices `"group1"' through `"groupN"' for some N, i.e., the total number of supplementary groups. However, we don't know in advance how many of these groups there are. This loop works by starting at one, concatenating the value with `"group"', and then using `in' to see if that value is in the array. Eventually, `i' is incremented past the last group in the array and the loop exits. The loop is also correct if there are _no_ supplementary groups; then the condition is false the first time it's tested, and the loop body never executes. d13031 5 a13035 2  File: gawk.info, Node: Split Program, Next: Tee Program, Prev: Id Program, Up: Clones d13037 6 a13042 2 Splitting a Large File into Pieces ---------------------------------- d13044 3 a13046 2 The `split' program splits large text files into smaller pieces. Usage is as follows: d13048 6 a13053 1 split [-COUNT] file [ PREFIX ] d13055 3 a13057 7 By default, the output files are named `xaa', `xab', and so on. Each file has 1000 lines in it, with the likely exception of the last file. To change the number of lines in each file, supply a number on the command line preceded with a minus; e.g., `-500' for files with 500 lines in them instead of 1000. To change the name of the output files to something like `myfileaa', `myfileab', and so on, supply an additional argument that specifies the file name prefix. d13059 6 a13064 27 Here is a version of `split' in `awk'. It uses the `ord' and `chr' functions presented in *Note Ordinal Functions::. The program first sets its defaults, and then tests to make sure there are not too many arguments. It then looks at each argument in turn. The first argument could be a minus sign followed by a number. If it is, this happens to look like a negative number, so it is made positive, and that is the count of lines. The data file name is skipped over and the final argument is used as the prefix for the output file names: # split.awk --- do split in awk # # Requires ord and chr library functions # usage: split [-num] [file] [outname] BEGIN { outfile = "x" # default count = 1000 if (ARGC > 4) usage() i = 1 if (ARGV[i] ~ /^-[0-9]+$/) { count = -ARGV[i] ARGV[i] = "" i++ d13066 4 a13069 6 # test argv in case reading from stdin instead of file if (i in ARGV) i++ # skip data file name if (i in ARGV) { outfile = ARGV[i] ARGV[i] = "" d13072 19 a13090 20 s1 = s2 = "a" out = (outfile s1 s2) } The next rule does most of the work. `tcount' (temporary count) tracks how many lines have been printed to the output file so far. If it is greater than `count', it is time to close the current file and start a new one. `s1' and `s2' track the current suffixes for the file name. If they are both `z', the file is just too big. Otherwise, `s1' moves to the next letter in the alphabet and `s2' starts over again at `a': { if (++tcount > count) { close(out) if (s2 == "z") { if (s1 == "z") { printf("split: %s is too large to split\n", FILENAME) > "/dev/stderr" exit 1 a13091 2 s1 = chr(ord(s1) + 1) s2 = "a" d13093 1 a13093 4 else s2 = chr(ord(s2) + 1) out = (outfile s1 s2) tcount = 1 a13094 1 print > out d13097 12 a13108 1 The `usage' function simply prints an error message and exits: d13110 1 a13110 1 function usage( e) d13112 2 a13113 2 e = "usage: split [-num] [file] [outname]" print e > "/dev/stderr" d13116 5 a13120 7 The variable `e' is used so that the function fits nicely on the screen. This program is a bit sloppy; it relies on `awk' to automatically close the last file instead of doing it in an `END' rule. It also assumes that letters are contiguous in the character set, which isn't true for EBCDIC systems. d13123 1 a13123 1 File: gawk.info, Node: Tee Program, Next: Uniq Program, Prev: Split Program, Up: Clones d13125 2 a13126 2 Duplicating Output into Multiple Files -------------------------------------- d13128 8 a13135 3 The `tee' program is known as a "pipe fitting." `tee' copies its standard input to its standard output and also duplicates it to the files named on the command line. Its usage is as follows: d13137 1 a13137 4 tee [-a] file ... The `-a' option tells `tee' to append to the named files, instead of truncating them and starting over. d13139 9 a13147 4 The `BEGIN' rule first makes a copy of all the command-line arguments into an array named `copy'. `ARGV[0]' is not copied, since it is not needed. `tee' cannot use `ARGV' directly, since `awk' attempts to process each file name in `ARGV' as input data. d13149 7 a13155 8 If the first argument is `-a', then the flag variable `append' is set to true, and both `ARGV[1]' and `copy[1]' are deleted. If `ARGC' is less than two, then no file names were supplied and `tee' prints a usage message and exits. Finally, `awk' is forced to read the standard input by setting `ARGV[1]' to `"-"' and `ARGC' to two: # tee.awk --- tee in awk BEGIN \ d13157 11 a13167 2 for (i = 1; i < ARGC; i++) copy[i] = ARGV[i] d13169 2 a13170 12 if (ARGV[1] == "-a") { append = 1 delete ARGV[1] delete copy[1] ARGC-- } if (ARGC < 2) { print "usage: tee [-a] file ..." > "/dev/stderr" exit 1 } ARGV[1] = "-" ARGC = 2 d13172 2 a13173 6 The single rule does all the work. Since there is no pattern, it is executed for each line of input. The body of the rule simply prints the line into each file on the command line, and then to the standard output: d13175 2 a13176 4 # moving the if outside the loop makes it run faster if (append) for (i in copy) print >> copy[i] d13178 1 a13178 3 for (i in copy) print > copy[i] print d13181 34 a13214 1 It is also possible to write the loop this way: d13216 2 a13217 5 for (i in copy) if (append) print >> copy[i] else print > copy[i] d13219 8 a13226 5 This is more concise but it is also less efficient. The `if' is tested for each record and for each output file. By duplicating the loop body, the `if' is only tested once for each input record. If there are N input records and M output files, the first method only executes N `if' statements, while the second executes N`*'M `if' statements. d13228 1 a13228 1 Finally, the `END' rule cleans up by closing all the output files: d13230 10 a13239 4 END \ { for (i in copy) close(copy[i]) d13242 11 a13252 2  File: gawk.info, Node: Uniq Program, Next: Wc Program, Prev: Tee Program, Up: Clones d13254 2 a13255 2 Printing Nonduplicated Lines of Text ------------------------------------ d13257 2 a13258 4 The `uniq' utility reads sorted lines of data on its standard input, and by default removes duplicate lines. In other words, it only prints unique lines--hence the name. `uniq' has a number of options. The usage is as follows: d13260 2 a13261 1 uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]] d13263 3 a13265 1 The options for `uniq' are: d13267 9 a13275 2 `-d' Pnly print only repeated lines. d13277 3 a13279 2 `-u' Print only nonrepeated lines. d13281 3 a13283 3 `-c' Count lines. This option overrides `-d' and `-u'. Both repeated and nonrepeated lines are counted. d13285 2 a13286 4 `-N' Skip N fields before comparing lines. The definition of fields is similar to `awk''s default: nonwhitespace characters separated by runs of spaces and/or tabs. d13288 3 a13290 3 `+N' Skip N characters before comparing lines. Any fields specified with `-N' are skipped first. d13292 6 a13297 3 `INPUT FILE' Data is read from the input file named on the command line, instead of from the standard input. d13299 3 a13301 3 `OUTPUT FILE' The generated output is sent to the named output file, instead of to the standard output. d13303 12 a13314 2 Normally `uniq' behaves as if both the `-d' and `-u' options are provided. d13316 19 a13334 2 `uniq' uses the `getopt' library function (*note Getopt Function::) and the `join' library function (*note Join Function::). d13336 1 a13336 16 The program begins with a `usage' function and then a brief outline of the options and their meanings in a comment. The `BEGIN' rule deals with the command-line arguments and options. It uses a trick to get `getopt' to handle options of the form `-25', treating such an option as the option letter `2' with an argument of `5'. If indeed two or more digits are supplied (`Optarg' looks like a number), `Optarg' is concatenated with the option digit and then the result is added to zero to make it into a number. If there is only one digit in the option, then `Optarg' is not needed. In this case, `Optind' must be decremented so that `getopt' processes it next time. This code is admittedly a bit tricky. If no options are supplied, then the default is taken, to print both repeated and nonrepeated lines. The output file, if provided, is assigned to `outputfile'. Early on, `outputfile' is initialized to the standard output, `/dev/stdout': d13338 38 a13375 9 # uniq.awk --- do uniq in awk # # Requires getopt and join library functions function usage( e) { e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]" print e > "/dev/stderr" exit 1 } d13377 3 a13379 5 # -c count lines. overrides -d and -u # -d only repeated lines # -u only non-repeated lines # -n skip n fields # +n skip n characters, skip fields first d13381 3 a13383 24 BEGIN \ { count = 1 outputfile = "/dev/stdout" opts = "udc0:1:2:3:4:5:6:7:8:9:" while ((c = getopt(ARGC, ARGV, opts)) != -1) { if (c == "u") non_repeated_only++ else if (c == "d") repeated_only++ else if (c == "c") do_count++ else if (index("0123456789", c) != 0) { # getopt requires args to options # this messes us up for things like -5 if (Optarg ~ /^[0-9]+$/) fcount = (c Optarg) + 0 else { fcount = c + 0 Optind-- } } else usage() } d13385 3 a13387 4 if (ARGV[Optind] ~ /^\+[0-9]+$/) { charcount = substr(ARGV[Optind], 2) + 0 Optind++ } d13389 4 a13392 2 for (i = 1; i < Optind; i++) ARGV[i] = "" d13394 1 a13394 2 if (repeated_only == 0 && non_repeated_only == 0) repeated_only = non_repeated_only = 1 d13396 4 a13399 24 if (ARGC - Optind == 2) { outputfile = ARGV[ARGC - 1] ARGV[ARGC - 1] = "" } } The following function, `are_equal', compares the current line, `$0', to the previous line, `last'. It handles skipping fields and characters. If no field count and no character count are specified, `are_equal' simply returns one or zero depending upon the result of a simple string comparison of `last' and `$0'. Otherwise, things get more complicated. If fields have to be skipped, each line is broken into an array using `split' (*note String Functions::); the desired fields are then joined back into a line using `join'. The joined lines are stored in `clast' and `cline'. If no fields are skipped, `clast' and `cline' are set to `last' and `$0', respectively. Finally, if characters are skipped, `substr' is used to strip off the leading `charcount' characters in `clast' and `cline'. The two strings are then compared and `are_equal' returns the result: function are_equal( n, m, clast, cline, alast, aline) { if (fcount == 0 && charcount == 0) return (last == $0) d13401 11 a13411 13 if (fcount > 0) { n = split(last, alast) m = split($0, aline) clast = join(alast, fcount+1, n) cline = join(aline, fcount+1, m) } else { clast = last cline = $0 } if (charcount) { clast = substr(clast, charcount + 1) cline = substr(cline, charcount + 1) } d13413 1 a13413 2 return (clast == cline) } d13415 9 a13423 4 The following two rules are the body of the program. The first one is executed only for the very first line of data. It sets `last' equal to `$0', so that subsequent lines of text have something to be compared to. d13425 9 a13433 14 The second rule does the work. The variable `equal' is one or zero, depending upon the results of `are_equal''s comparison. If `uniq' is counting repeated lines, and the lines are equal, then it increments the `count' variable. Otherwise, it prints the line and resets `count', since the two lines are not equal. If `uniq' is not counting, and if the lines are equal, `count' is incremented. Nothing is printed, since the point is to remove duplicates. Otherwise, if `uniq' is counting repeated lines and more than one line is seen, or if `uniq' is counting nonrepeated lines and only one line is seen, then the line is printed, and `count' is reset. Finally, similar logic is used in the `END' rule to print the final line of input data: d13435 2 a13436 4 NR == 1 { last = $0 next } d13438 1 d13440 2 a13441 1 equal = are_equal() d13443 6 a13448 7 if (do_count) { # overrides -d and -u if (equal) count++ else { printf("%4d %s\n", count, last) > outputfile last = $0 count = 1 # reset a13449 1 next d13451 1 a13451 18 if (equal) count++ else { if ((repeated_only && count > 1) || (non_repeated_only && count == 1)) print last > outputfile last = $0 count = 1 } } END { if (do_count) printf("%4d %s\n", count, last) > outputfile else if ((repeated_only && count > 1) || (non_repeated_only && count == 1)) print last > outputfile d13454 4 a13457 2  File: gawk.info, Node: Wc Program, Prev: Uniq Program, Up: Clones d13459 7 a13465 12 Counting Things --------------- The `wc' (word count) utility counts lines, words, and characters in one or more input files. Its usage is as follows: wc [-lwc] [ FILES ... ] If no files are specified on the command line, `wc' reads its standard input. If there are multiple files, it also prints total counts for all the files. The options and their meanings are shown in the following list: d13467 14 a13480 24 `-l' Count only lines. `-w' Count only words. A "word" is a contiguous sequence of nonwhitespace characters, separated by spaces and/or tabs. Luckily, this is the normal way `awk' separates fields in its input data. `-c' Count only characters. Implementing `wc' in `awk' is particularly elegant, since `awk' does a lot of the work for us; it splits lines into words (i.e., fields) and counts them, it counts lines (i.e., records), and it can easily tell us how long a line is. This uses the `getopt' library function (*note Getopt Function::) and the file-transition functions (*note Filetrans Function::). This version has one notable difference from traditional versions of `wc': it always prints the counts in the order lines, words, and characters. Traditional versions note the order of the `-l', `-w', and `-c' options on the command line, and print the counts in that order. d13482 3 a13484 3 The `BEGIN' rule does the argument processing. The variable `print_total' is true if more than one file is named on the command line: d13486 2 a13487 1 # wc.awk --- count lines, words, characters d13489 21 a13509 19 # Options: # -l only count lines # -w only count words # -c only count characters # # Default is to count lines, words, characters # # Requires getopt and file transition library functions BEGIN { # let getopt print a message about # invalid options. we ignore them while ((c = getopt(ARGC, ARGV, "lwc")) != -1) { if (c == "l") do_lines = 1 else if (c == "w") do_words = 1 else if (c == "c") do_chars = 1 d13511 7 a13517 2 for (i = 1; i < Optind; i++) ARGV[i] = "" d13519 8 a13526 6 # if no options, do all if (! do_lines && ! do_words && ! do_chars) do_lines = do_words = do_chars = 1 print_total = (ARGC - i > 2) } d13528 4 a13531 3 The `beginfile' function is simple; it just resets the counts of lines, words, and characters to zero, and saves the current file name in `fname': d13533 3 a13535 5 function beginfile(file) { chars = lines = words = 0 fname = FILENAME } d13537 5 a13541 4 The `endfile' function adds the current file's numbers to the running totals of lines, words, and characters.(1) It then prints out those numbers for the file that was just read. It relies on `beginfile' to reset the numbers for the following data file: d13543 4 a13546 13 function endfile(file) { tchars += chars tlines += lines twords += words if (do_lines) printf "\t%d", lines if (do_words) printf "\t%d", words if (do_chars) printf "\t%d", chars printf "\t%s\n", fname } d13548 2 a13549 7 There is one rule that is executed for each line. It adds the length of the record, plus one, to `chars'. Adding one plus the record length is needed because the newline character separating records (the value of `RS') is not part of the record itself, and thus not included in its length. Next, `lines' is incremented for each line read, and `words' is incremented by the value of `NF', which is the number of "words" on this line: d13551 3 a13553 6 # do per line { chars += length($0) + 1 # get newline lines++ words += NF } d13555 6 a13560 1 Finally, the `END' rule simply prints the totals for all the files: d13562 5 a13566 11 END { if (print_total) { if (do_lines) printf "\t%d", tlines if (do_words) printf "\t%d", twords if (do_chars) printf "\t%d", tchars print "\ttotal" } } d13570 2 a13571 3 (1) `wc' can't just use the value of `FNR' in `endfile'. If you examine the code in *Note Filetrans Function:: you will see that `FNR' has already been reset by the time `endfile' is called. d13574 1 a13574 1 File: gawk.info, Node: Miscellaneous Programs, Prev: Clones, Up: Sample Programs d13576 2 a13577 2 A Grab Bag of `awk' Programs ============================ d13579 8 a13586 2 This minor node is a large "grab bag" of miscellaneous programs. We hope you find them both interesting and enjoyable. d13590 9 a13598 12 * Dupword Program:: Finding duplicated words in a document. * Alarm Program:: An alarm clock. * Translate Program:: A program similar to the `tr' utility. * Labels Program:: Printing mailing labels. * Word Sorting:: A program to produce a word usage count. * History Sorting:: Eliminating duplicate entries from a history file. * Extract Program:: Pulling out programs from Texinfo source files. * Simple Sed:: A Simple Stream Editor. * Igawk Program:: A wrapper for `awk' that includes files. d13601 1 a13601 1 File: gawk.info, Node: Dupword Program, Next: Alarm Program, Up: Miscellaneous Programs d13603 13 a13615 2 Finding Duplicated Words in a Document -------------------------------------- d13617 1 a13617 5 A common error when writing large amounts of prose is to accidentally duplicate words. Typically you will see this in text as something like "the the program does the following..." When the text is online, often the duplicated words occur at the end of one line and the beginning of another, making them very difficult to spot. d13619 2 a13620 4 This program, `dupword.awk', scans through a file one line at a time and looks for adjacent occurrences of the same word. It also saves the last word on a line (in the variable `prev') for comparison with the first word on the next line. d13622 2 a13623 13 The first two statements make sure that the line is all lowercase, so that, for example, "The" and "the" compare equal to each other. The next statement replaces nonalphanumeric and nonwhitespace characters with spaces, so that punctuation does not affect the comparison either. The characters are replaced with spaces so that formatting controls don't create nonsense words (e.g., the Texinfo `@@code{NF}' becomes `codeNF' if punctuation is simply deleted). The record is then resplit into fields, yielding just the actual words on the line, and ensuring that there are no empty fields. If there are no fields left after removing all the punctuation, the current record is skipped. Otherwise, the program loops through each word, comparing it to the previous one: d13625 2 a13626 16 # dupword.awk --- find duplicate words in text { $0 = tolower($0) gsub(/[^[:alnum:][:blank:]]/, " "); $0 = $0 # re-split if (NF == 0) next if ($1 == prev) printf("%s:%d: duplicate %s\n", FILENAME, FNR, $1) for (i = 2; i <= NF; i++) if ($i == $(i-1)) printf("%s:%d: duplicate %s\n", FILENAME, FNR, $i) prev = $NF } d13628 2 a13629 2  File: gawk.info, Node: Alarm Program, Next: Translate Program, Prev: Dupword Program, Up: Miscellaneous Programs d13631 2 a13632 2 An Alarm Clock Program ---------------------- d13634 2 a13635 2 Nothing cures insomnia like a ringing alarm clock. Arnold Robbins d13637 3 a13639 5 The following program is a simple "alarm clock" program. You give it a time of day and an optional message. At the specified time, it prints the message on the standard output. In addition, you can give it the number of times to repeat the message as well as a delay between repetitions. d13641 3 a13643 2 This program uses the `gettimeofday' function from *Note Gettimeofday Function::. d13645 4 a13648 8 All the work is done in the `BEGIN' rule. The first part is argument checking and setting of defaults: the delay, the count, and the message to print. If the user supplied a message without the ASCII BEL character (known as the "alert" character, `"\a"'), then it is added to the message. (On many systems, printing the ASCII BEL generates an audible alert. Thus when the alarm goes off, the system calls attention to itself in case the user is not looking at the computer or terminal.) Here is the program: d13650 2 a13651 39 # alarm.awk --- set an alarm # # Requires gettimeofday library function # usage: alarm time [ "message" [ count [ delay ] ] ] BEGIN \ { # Initial argument sanity checking usage1 = "usage: alarm time ['message' [count [delay]]]" usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1]) if (ARGC < 2) { print usage1 > "/dev/stderr" print usage2 > "/dev/stderr" exit 1 } else if (ARGC == 5) { delay = ARGV[4] + 0 count = ARGV[3] + 0 message = ARGV[2] } else if (ARGC == 4) { count = ARGV[3] + 0 message = ARGV[2] } else if (ARGC == 3) { message = ARGV[2] } else if (ARGV[1] !~ /[0-9]?[0-9]:[0-9][0-9]/) { print usage1 > "/dev/stderr" print usage2 > "/dev/stderr" exit 1 } # set defaults for once we reach the desired time if (delay == 0) delay = 180 # 3 minutes if (count == 0) count = 5 if (message == "") message = sprintf("\aIt is now %s!\a", ARGV[1]) else if (index(message, "\a") == 0) message = "\a" message "\a" d13653 4 a13656 6 The next minor node of code turns the alarm time into hours and minutes, converts it (if necessary) to a 24-hour clock, and then turns that time into a count of the seconds since midnight. Next it turns the current time into a count of seconds since midnight. The difference between the two is how long to wait before setting off the alarm: d13658 2 a13659 27 # split up alarm time split(ARGV[1], atime, ":") hour = atime[1] + 0 # force numeric minute = atime[2] + 0 # force numeric # get current broken down time gettimeofday(now) # if time given is 12-hour hours and it's after that # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m., # then add 12 to real hour if (hour < 12 && now["hour"] > hour) hour += 12 # set target time in seconds since midnight target = (hour * 60 * 60) + (minute * 60) # get current time in seconds since midnight current = (now["hour"] * 60 * 60) + \ (now["minute"] * 60) + now["second"] # how long to sleep for naptime = target - current if (naptime <= 0) { print "time is in the past!" > "/dev/stderr" exit 1 } d13661 2 a13662 7 Finally, the program uses the `system' function (*note I/O Functions::) to call the `sleep' utility. The `sleep' utility simply pauses for the given number of seconds. If the exit status is not zero, the program assumes that `sleep' was interrupted and exits. If `sleep' exited with an OK status (zero), then the program prints the message in a loop, again using `sleep' to delay for however many seconds are necessary: d13664 2 a13665 15 # zzzzzz..... go away if interrupted if (system(sprintf("sleep %d", naptime)) != 0) exit 1 # time to notify! command = sprintf("sleep %d", delay) for (i = 1; i <= count; i++) { print message # if sleep command interrupted, go away if (system(command) != 0) break } exit 0 } d13668 4 a13671 1 File: gawk.info, Node: Translate Program, Next: Labels Program, Prev: Alarm Program, Up: Miscellaneous Programs d13673 2 a13674 2 Transliterating Characters -------------------------- d13676 1 a13676 3 The system `tr' utility transliterates characters. For example, it is often used to map uppercase letters into lowercase for further processing: d13678 2 a13679 1 GENERATE DATA | tr 'A-Z' 'a-z' | PROCESS DATA ... d13681 2 a13682 13 `tr' requires two lists of characters.(1) When processing the input, the first character in the first list is replaced with the first character in the second list, the second character in the first list is replaced with the second character in the second list, and so on. If there are more characters in the "from" list than in the "to" list, the last character of the "to" list is used for the remaining characters in the "from" list. Some time ago, a user proposed that a transliteration function should be added to `gawk'. The following program was written to prove that character transliteration could be done with a user-level function. This program is not as complete as the system `tr' utility but it does most of the job. d13684 1 a13684 5 The `translate' program demonstrates one of the few weaknesses of standard `awk': dealing with individual characters is very painful, requiring repeated use of the `substr', `index', and `gsub' built-in functions (*note String Functions::).(2) There are two functions. The first, `stranslate', takes three arguments: d13686 2 a13687 2 `from' A list of characters from which to translate. d13689 2 a13690 2 `to' A list of characters to which to translate. d13692 3 a13694 2 `target' The string on which to do the translation. d13696 2 a13697 5 Associative arrays make the translation part fairly easy. `t_ar' holds the "to" characters, indexed by the "from" characters. Then a simple loop goes through `from', one character at a time. For each character in `from', if the character appears in `target', `gsub' is used to change it to the corresponding `to' character. d13699 3 a13701 4 The `translate' function simply calls `stranslate' using `$0' as the target. The main program sets two global variables, `FROM' and `TO', from the command line, and then changes `ARGV' so that `awk' reads from the standard input. d13703 4 a13706 2 Finally, the processing rule simply calls `translate' for each record: d13708 2 a13709 43 # translate.awk --- do tr-like stuff # Bugs: does not handle things like: tr A-Z a-z, it has # to be spelled out. However, if `to' is shorter than `from', # the last character in `to' is used for the rest of `from'. function stranslate(from, to, target, lf, lt, t_ar, i, c) { lf = length(from) lt = length(to) for (i = 1; i <= lt; i++) t_ar[substr(from, i, 1)] = substr(to, i, 1) if (lt < lf) for (; i <= lf; i++) t_ar[substr(from, i, 1)] = substr(to, lt, 1) for (i = 1; i <= lf; i++) { c = substr(from, i, 1) if (index(target, c) > 0) gsub(c, t_ar[c], target) } return target } function translate(from, to) { return $0 = stranslate(from, to, $0) } # main program BEGIN { if (ARGC < 3) { print "usage: translate from to" > "/dev/stderr" exit } FROM = ARGV[1] TO = ARGV[2] ARGC = 2 ARGV[1] = "-" } { translate(FROM, TO) print } d13711 2 a13712 8 While it is possible to do character transliteration in a user-level function, it is not necessarily efficient, and we (the `gawk' authors) started to consider adding a built-in function. However, shortly after writing this program, we learned that the System V Release 4 `awk' had added the `toupper' and `tolower' functions (*note String Functions::). These functions handle the vast majority of the cases where character transliteration is necessary, and so we chose to simply add those functions to `gawk' as well and then leave well enough alone. d13714 2 a13715 4 An obvious improvement to this program would be to set up the `t_ar' array only once, in a `BEGIN' rule. However, this assumes that the "from" and "to" lists will never change throughout the lifetime of the program. d13717 1 a13717 1 ---------- Footnotes ---------- d13719 2 a13720 4 (1) On some older System V systems, `tr' may require that the lists be written as range expressions enclosed in square brackets (`[a-z]') and quoted, to prevent the shell from attempting a file name expansion. This is not a feature. d13722 3 a13724 2 (2) This program was written before `gawk' acquired the ability to split each character in a string into separate array elements. d13726 2 a13727 2  File: gawk.info, Node: Labels Program, Next: Word Sorting, Prev: Translate Program, Up: Miscellaneous Programs d13729 2 a13730 2 Printing Mailing Labels ----------------------- d13732 2 a13733 5 Here is a "real world"(1) program. This script reads lists of names and addresses and generates mailing labels. Each page of labels has 20 labels on it, 2 across and 10 down. The addresses are guaranteed to be no more than 5 lines of data. Each address is separated from the next by a blank line. d13735 2 a13736 4 The basic idea is to read 20 labels worth of data. Each line of each label is stored in the `line' array. The single rule takes care of filling the `line' array and printing the page when 20 labels have been read. d13738 2 a13739 4 The `BEGIN' rule simply sets `RS' to the empty string, so that `awk' splits records at blank lines (*note Records::). It sets `MAXLINES' to 100, since 100 is the maximum number of lines on the page (20 * 5 = 100). d13741 3 a13743 9 Most of the work is done in the `printpage' function. The label lines are stored sequentially in the `line' array. But they have to print horizontally; `line[1]' next to `line[6]', `line[2]' next to `line[7]', and so on. Two loops are used to accomplish this. The outer loop, controlled by `i', steps through every 10 lines of data; this is each row of labels. The inner loop, controlled by `j', goes through the lines within the row. As `j' goes from 0 to 4, `i+j' is the `j'-th line in the row, and `i+j+5' is the entry next to it. The output ends up looking something like this: d13745 3 a13747 6 line 1 line 6 line 2 line 7 line 3 line 8 line 4 line 9 line 5 line 10 ... d13749 2 a13750 5 As a final note, an extra blank line is printed at lines 21 and 61, to keep the output lined up on the labels. This is dependent on the particular brand of labels in use when the program was written. You will also note that there are 2 blank lines at the top and 2 blank lines at the bottom. d13752 2 a13753 2 The `END' rule arranges to flush the final page of labels; there may not have been an even multiple of 20 labels in the data: d13755 2 a13756 51 # labels.awk --- print mailing labels # Each label is 5 lines of data that may have blank lines. # The label sheets have 2 blank lines at the top and 2 at # the bottom. BEGIN { RS = "" ; MAXLINES = 100 } function printpage( i, j) { if (Nlines <= 0) return printf "\n\n" # header for (i = 1; i <= Nlines; i += 10) { if (i == 21 || i == 61) print "" for (j = 0; j < 5; j++) { if (i + j > MAXLINES) break printf " %-41s %s\n", line[i+j], line[i+j+5] } print "" } printf "\n\n" # footer for (i in line) line[i] = "" } # main rule { if (Count >= 20) { printpage() Count = 0 Nlines = 0 } n = split($0, a, "\n") for (i = 1; i <= n; i++) line[++Nlines] = a[i] for (; i <= 5; i++) line[++Nlines] = "" Count++ } END \ { printpage() } d13758 9 a13766 1 ---------- Footnotes ---------- d13768 2 a13769 2 (1) "Real world" is defined as "a program actually used to get something done." d13772 9 a13780 1 File: gawk.info, Node: Word Sorting, Next: History Sorting, Prev: Labels Program, Up: Miscellaneous Programs d13782 1 a13782 2 Generating Word-Usage Counts ---------------------------- d13784 3 a13786 7 The following `awk' program prints the number of occurrences of each word in its input. It illustrates the associative nature of `awk' arrays by using strings as subscripts. It also demonstrates the `for INDEX in ARRAY' mechanism. Finally, it shows how `awk' is used in conjunction with other utility programs to do a useful task of some complexity with a minimum of effort. Some explanations follow the program listing: d13788 2 a13789 10 # Print list of word frequencies { for (i = 1; i <= NF; i++) freq[$i]++ } END { for (word in freq) printf "%s\t%d\n", word, freq[word] } d13791 3 a13793 7 This program has two rules. The first rule, because it has an empty pattern, is executed for every input line. It uses `awk''s field-accessing mechanism (*note Fields::) to pick out the individual words from the line, and the built-in variable `NF' (*note Built-in Variables::) to know how many fields are available. For each input word, it increments an element of the array `freq' to reflect that the word has been seen an additional time. d13795 1 a13795 5 The second rule, because it has the pattern `END', is not executed until the input has been exhausted. It prints out the contents of the `freq' table that has been built up inside the first action. This program has several problems that would prevent it from being useful by itself on real text files: d13797 2 a13798 4 * Words are detected using the `awk' convention that fields are separated just by whitespace. Other characters in the input (except newlines) don't have any special meaning to `awk'. This means that punctuation characters count as part of words. d13800 3 a13802 5 * The `awk' language considers upper- and lowercase characters to be distinct. Therefore, "bartender" and "Bartender" are not treated as the same word. This is undesirable, since in normal text, words are capitalized if they begin sentences, and a frequency analyzer should not be sensitive to capitalization. d13804 2 a13805 3 * The output does not come out in any useful order. You're more likely to be interested in which words occur most frequently or in having an alphabetized table of how frequently each word occurs. d13807 2 a13808 5 The way to solve these problems is to use some of `awk''s more advanced features. First, we use `tolower' to remove case distinctions. Next, we use `gsub' to remove punctuation characters. Finally, we use the system `sort' utility to process the output of the `awk' script. Here is the new version of the program: d13810 2 a13811 14 # wordfreq.awk --- print list of word frequencies { $0 = tolower($0) # remove case distinctions # remove punctuation gsub(/[^[:alnum:]_[:blank:]]/, "", $0) for (i = 1; i <= NF; i++) freq[$i]++ } END { for (word in freq) printf "%s\t%d\n", word, freq[word] } d13813 1 a13813 2 Assuming we have saved this program in a file named `wordfreq.awk', and that the data is in `file1', the following pipeline: d13815 2 a13816 1 awk -f wordfreq.awk file1 | sort -k 2nr d13818 1 a13818 3 produces a table of the words appearing in `file1' in order of decreasing frequency. The `awk' program suitably massages the data and produces a word frequency table, which is not ordered. d13820 2 a13821 6 The `awk' script's output is then sorted by the `sort' utility and printed on the terminal. The options given to `sort' specify a sort that uses the second field of each input line (skipping one field), that the sort keys should be treated as numeric quantities (otherwise `15' would come before `5'), and that the sorting should be done in descending (reverse) order. d13823 3 a13825 2 The `sort' could even be done from within the program, by changing the `END' action to: d13827 2 a13828 6 END { sort = "sort -k 2nr" for (word in freq) printf "%s\t%d\n", word, freq[word] | sort close(sort) } d13830 2 a13831 4 This way of sorting must be used on systems that do not have true pipes at the command-line (or batch-file) level. See the general operating system documentation for more information on how to use the `sort' program. d13833 3 a13835 2  File: gawk.info, Node: History Sorting, Next: Extract Program, Prev: Word Sorting, Up: Miscellaneous Programs d13837 1 a13837 2 Removing Duplicates from Unsorted Text -------------------------------------- d13839 2 a13840 2 The `uniq' program (*note Uniq Program::), removes duplicate lines from _sorted_ data. d13842 3 a13844 7 Suppose, however, you need to remove duplicate lines from a data file but that you want to preserve the order the lines are in. A good example of this might be a shell history file. The history file keeps a copy of all the commands you have entered, and it is not unusual to repeat a command several times in a row. Occasionally you might want to compact the history by removing duplicate entries. Yet it is desirable to maintain the order of the original commands. d13846 2 a13847 7 This simple program does the job. It uses two arrays. The `data' array is indexed by the text of each line. For each line, `data[$0]' is incremented. If a particular line has not been seen before, then `data[$0]' is zero. In this case, the text of the line is stored in `lines[count]'. Each element of `lines' is a unique command, and the indices of `lines' indicate the order in which those lines are encountered. The `END' rule simply prints out the lines, in order: d13849 3 a13851 11 # histsort.awk --- compact a shell history file # Thanks to Byron Rakitzis for the general idea { if (data[$0]++ == 0) lines[++count] = $0 } END { for (i = 1; i <= count; i++) print lines[i] } d13853 2 a13854 3 This program also provides a foundation for generating other useful information. For example, using the following `print' statement in the `END' rule indicates how often a particular command is used: d13856 2 a13857 1 print data[lines[i]], lines[i] d13859 2 a13860 2 This works because `data[$0]' is incremented each time a line is seen. d13862 3 a13864 2  File: gawk.info, Node: Extract Program, Next: Simple Sed, Prev: History Sorting, Up: Miscellaneous Programs d13866 2 a13867 2 Extracting Programs from Texinfo Source Files --------------------------------------------- d13869 2 a13870 5 The nodes *Note Library Functions::, and *Note Sample Programs::, are the top level nodes for a large number of `awk' programs. If you want to experiment with these programs, it is tedious to have to type them in by hand. Here we present a program that can extract parts of a Texinfo input file into separate files. d13872 3 a13874 4 This Info file is written in Texinfo, the GNU project's document formatting language. A single Texinfo source file can be used to produce both printed and online documentation. The Texinfo language is described fully, starting with *Note Top::. d13876 3 a13878 2 For our purposes, it is enough to know three things about Texinfo input files: d13880 2 a13881 3 * The "at" symbol (`@@') is special in Texinfo, much as the backslash (`\') is in C or `awk'. Literal `@@' symbols are represented in Texinfo source files as `@@@@'. d13883 2 a13884 3 * Comments start with either `@@c' or `@@comment'. The file-extraction program works by using special comments that start at the beginning of a line. d13886 2 a13887 4 * Lines containing `@@group' and `@@end group' commands bracket example text that should not be split across a page boundary. (Unfortunately, TeX isn't always smart enough to do things exactly right, and we have to give it some help.) d13889 2 a13890 17 The following program, `extract.awk', reads through a Texinfo source file and does two things, based on the special comments. Upon seeing `@@c system ...', it runs a command, by extracting the command text from the control line and passing it on to the `system' function (*note I/O Functions::). Upon seeing `@@c file FILENAME', each subsequent line is sent to the file FILENAME, until `@@c endfile' is encountered. The rules in `extract.awk' match either `@@c' or `@@comment' by letting the `omment' part be optional. Lines containing `@@group' and `@@end group' are simply removed. `extract.awk' uses the `join' library function (*note Join Function::). The example programs in the online Texinfo source for `GAWK: Effective AWK Programming' (`gawk.texi') have all been bracketed inside `file' and `endfile' lines. The `gawk' distribution uses a copy of `extract.awk' to extract the sample programs and install many of them in a standard directory where `gawk' can find them. The Texinfo file looks something like this: d13892 3 a13894 18 ... This program has a @@code{BEGIN} rule, that prints a nice message: @@example @@c file examples/messages.awk BEGIN @@{ print "Don't panic!" @@} @@c end file @@end example It also prints some final advice: @@example @@c file examples/messages.awk END @@{ print "Always avoid bored archeologists!" @@} @@c end file @@end example ... d13896 1 a13896 2 `extract.awk' begins by setting `IGNORECASE' to one, so that mixed upper- and lowercase letters in the directives won't matter. d13898 8 a13905 3 The first rule handles calling `system', checking that a command is given (`NF' is at least three) and also checking that the command exits with a zero exit status, signifying OK: d13907 2 a13908 21 # extract.awk --- extract files and run programs # from texinfo files BEGIN { IGNORECASE = 1 } /^@@c(omment)?[ \t]+system/ \ { if (NF < 3) { e = (FILENAME ":" FNR) e = (e ": badly formed `system' line") print e > "/dev/stderr" next } $1 = "" $2 = "" stat = system($0) if (stat != 0) { e = (FILENAME ":" FNR) e = (e ": warning: system returned " stat) print e > "/dev/stderr" } } d13910 2 a13911 1 The variable `e' is used so that the function fits nicely on the screen. d13913 3 a13915 6 The second rule handles moving data into files. It verifies that a file name is given in the directive. If the file named is not the current file, then the current file is closed. Keeping the current file open until a new file is encountered allows the use of the `>' redirection for printing the contents, keeping open file management simple. d13917 2 a13918 6 The `for' loop does the work. It reads lines using `getline' (*note Getline::). For an unexpected end of file, it calls the `unexpected_eof' function. If the line is an "endfile" line, then it breaks out of the loop. If the line is an `@@group' or `@@end group' line, then it ignores it and goes on to the next line. Similarly, comments within examples are also ignored. d13920 1 a13920 9 Most of the work is in the following few lines. If the line has no `@@' symbols, the program can print it directly. Otherwise, each leading `@@' must be stripped off. To remove the `@@' symbols, the line is split into separate elements of the array `a', using the `split' function (*note String Functions::). The `@@' symbol is used as the separator character. Each element of `a' that is empty indicates two successive `@@' symbols in the original line. For each two empty elements (`@@@@' in the original file), we have to add a single `@@' symbol back in. d13922 4 a13925 3 When the processing of the array is finished, `join' is called with the value of `SUBSEP', to rejoin the pieces back into a single line. That line is then printed to the output file: d13927 11 a13937 39 /^@@c(omment)?[ \t]+file/ \ { if (NF != 3) { e = (FILENAME ":" FNR ": badly formed `file' line") print e > "/dev/stderr" next } if ($3 != curfile) { if (curfile != "") close(curfile) curfile = $3 } for (;;) { if ((getline line) <= 0) unexpected_eof() if (line ~ /^@@c(omment)?[ \t]+endfile/) break else if (line ~ /^@@(end[ \t]+)?group/) continue else if (line ~ /^@@c(omment+)?[ \t]+/) continue if (index(line, "@@") == 0) { print line > curfile continue } n = split(line, a, "@@") # if a[1] == "", means leading @@, # don't add one back in. for (i = 2; i <= n; i++) { if (a[i] == "") { # was an @@@@ a[i] = "@@" if (a[i+1] == "") i++ } } print join(a, 1, n, SUBSEP) > curfile } } d13939 4 a13942 7 An important thing to note is the use of the `>' redirection. Output done with `>' only opens the file once; it stays open and subsequent output is appended to the file (*note Redirection::). This makes it easy to mix program text and explanatory prose for the same sample source file (as has been done here!) without any hassle. The file is only closed when a new data file name is encountered or at the end of the input file. d13944 5 a13948 3 Finally, the function `unexpected_eof' prints an appropriate error message and then exits. The `END' rule handles the final cleanup, closing the open file: d13950 7 a13956 10 function unexpected_eof() { printf("%s:%d: unexpected EOF or error\n", FILENAME, FNR) > "/dev/stderr" exit 1 } END { if (curfile) close(curfile) } d13958 6 a13963 2  File: gawk.info, Node: Simple Sed, Next: Igawk Program, Prev: Extract Program, Up: Miscellaneous Programs d13965 3 a13967 2 A Simple Stream Editor ---------------------- d13969 4 a13972 6 The `sed' utility is a stream editor, a program that reads a stream of data, makes changes to it, and passes it on. It is often used to make global changes to a large file or to a stream of data generated by a pipeline of commands. While `sed' is a complicated program in its own right, its most common use is to perform global substitutions in the middle of a pipeline: d13974 4 a13977 1 command1 < orig.data | sed 's/old/new/g' | command2 > result d13979 4 a13982 9 Here, `s/old/new/g' tells `sed' to look for the regexp `old' on each input line and globally replace it with the text `new', i.e., all the occurrences on a line. This is similar to `awk''s `gsub' function (*note String Functions::). The following program, `awksed.awk', accepts at least two command-line arguments: the pattern to look for and the text to replace it with. Any additional arguments are treated as data file names to process. If none are provided, the standard input is used: d13984 6 a13989 27 # awksed.awk --- do s/foo/bar/g using just print # Thanks to Michael Brennan for the idea function usage() { print "usage: awksed pat repl [files...]" > "/dev/stderr" exit 1 } BEGIN { # validate arguments if (ARGC < 3) usage() RS = ARGV[1] ORS = ARGV[2] # don't use arguments as files ARGV[1] = ARGV[2] = "" } # look ma, no hands! { if (RT == "") printf "%s", $0 else print } d13991 4 a13994 9 The program relies on `gawk''s ability to have `RS' be a regexp, as well as on the setting of `RT' to the actual text that terminates the record (*note Records::). The idea is to have `RS' be the pattern to look for. `gawk' automatically sets `$0' to the text between matches of the pattern. This is text that we want to keep, unmodified. Then, by setting `ORS' to the replacement text, a simple `print' statement outputs the text we want to keep, followed by the replacement text. d13996 4 a13999 6 There is one wrinkle to this scheme, which is what to do if the last record doesn't end with text that matches `RS'. Using a `print' statement unconditionally prints the replacement text, which is not correct. However, if the file did not end in text that matches `RS', `RT' is set to the null string. In this case, we can print `$0' using `printf' (*note Printf::). d14001 2 a14002 9 The `BEGIN' rule handles the setup, checking for the right number of arguments and calling `usage' if there is a problem. Then it sets `RS' and `ORS' from the command-line arguments and sets `ARGV[1]' and `ARGV[2]' to the null string, so that they are not treated as file names (*note ARGC and ARGV::). The `usage' function prints an error message and exits. Finally, the single rule handles the printing scheme outlined above, using `print' or `printf' as appropriate, depending upon the value of `RT'. d14005 4 a14008 1 File: gawk.info, Node: Igawk Program, Prev: Simple Sed, Up: Miscellaneous Programs d14010 41 a14050 2 An Easy Way to Use Library Functions ------------------------------------ d14052 1 a14052 8 Using library functions in `awk' can be very beneficial. It encourages code reuse and the writing of general functions. Programs are smaller and therefore clearer. However, using library functions is only easy when writing `awk' programs; it is painful when running them, requiring multiple `-f' options. If `gawk' is unavailable, then so too is the `AWKPATH' environment variable and the ability to put `awk' functions into a library directory (*note Options::). It would be nice to be able to write programs in the following manner: d14054 2 a14055 11 # library functions @@include getopt.awk @@include join.awk ... # main program BEGIN { while ((c = getopt(ARGC, ARGV, "a:b:cde")) != -1) ... ... } d14057 2 a14058 6 The following program, `igawk.sh', provides this service. It simulates `gawk''s searching of the `AWKPATH' variable and also allows "nested" includes; i.e., a file that is included with `@@include' can contain further `@@include' statements. `igawk' makes an effort to only include files once, so that nested includes don't accidentally include a library function twice. d14060 2 a14061 4 `igawk' should behave just like `gawk' externally. This means it should accept all of `gawk''s command-line arguments, including the ability to have multiple source files specified via `-f', and the ability to mix command-line and library source files. d14063 5 a14067 2 The program is written using the POSIX Shell (`sh') command language.(1) It works as follows: d14069 1 a14069 2 1. Loop through the arguments, saving anything that doesn't represent `awk' source code for later, when the expanded program is run. d14071 41 a14111 2 2. For any arguments that do represent `awk' text, put the arguments into a shell variable that will be expanded. There are two cases: d14113 1 a14113 2 a. Literal text, provided with `--source' or `--source='. This text is just appended directly. d14115 1 a14115 9 b. Source file names, provided with `-f'. We use a neat trick and append `@@include FILENAME' to the shell variable's contents. Since the file-inclusion program works the way `gawk' does, this gets the text of the file included into the program at the correct point. 3. Run an `awk' program (naturally) over the shell variable's contents to expand `@@include' statements. The expanded program is placed in a second shell variable. d14117 2 a14118 3 4. Run the expanded program with `gawk' and any other original command-line arguments that the user supplied (such as the data file names). d14120 2 a14121 6 This program uses shell variables extensively; for storing command line arguments, the text of the `awk' program that will expand the user's program, for the user's original program, and for the expanded program. Doing so removes some potential problems that might arise were we to use temporary files instead, at the cost of making the script somewhat more complicated. d14123 1 a14123 2 The initial part of the program turns on shell tracing if the first argument is `debug'. d14125 15 a14139 2 The next part loops through all the command-line arguments. There are several cases of interest: d14141 2 a14142 3 `--' This ends the arguments to `igawk'. Anything else should be passed on to the user's `awk' program without being evaluated. d14144 3 a14146 6 `-W' This indicates that the next option is specific to `gawk'. To make argument processing easier, the `-W' is appended to the front of the remaining arguments and the loop continues. (This is an `sh' programming trick. Don't worry about it if you are not familiar with `sh'.) d14148 16 a14163 2 `-v, -F' These are saved and passed on to `gawk'. d14165 3 a14167 23 `-f, --file, --file=, -Wfile=' The file name is appended to the shell variable `program' with an `@@include' statement. The `expr' utility is used to remove the leading option part of the argument (e.g., `--file='). (Typical `sh' usage would be to use the `echo' and `sed' utilities to do this work. Unfortunately, some versions of `echo' evaluate escape sequences in their arguments, possibly mangling the program text. Using `expr' avoids this problem.) `--source, --source=, -Wsource=' The source text is appended to `program'. `--version, -Wversion' `igawk' prints its version number, runs `gawk --version' to get the `gawk' version information, and then exits. If none of the `-f', `--file', `-Wfile', `--source', or `-Wsource' arguments are supplied, then the first nonoption argument should be the `awk' program. If there are no command-line arguments left, `igawk' prints an error message and exits. Otherwise, the first argument is appended to `program'. In any case, after the arguments have been processed, `program' contains the complete text of the original `awk' program. d14169 2 a14170 1 The program is as follows: d14172 2 a14173 73 #! /bin/sh # igawk --- like gawk but do @@include processing if [ "$1" = debug ] then set -x shift fi # A literal newline, so that program text is formmatted correctly n=' ' # Initialize variables to empty program= opts= while [ $# -ne 0 ] # loop over arguments do case $1 in --) shift; break;; -W) shift # The ${x?'message here'} construct prints a # diagnostic if $x is the null string set -- -W"${@@?'missing operand'}" continue;; -[vF]) opts="$opts $1 '${2?'missing operand'}'" shift;; -[vF]*) opts="$opts '$1'" ;; -f) program="$program$n@@include ${2?'missing operand'}" shift;; -f*) f=`expr "$1" : '-f\(.*\)'` program="$program$n@@include $f";; -[W-]file=*) f=`expr "$1" : '-.file=\(.*\)'` program="$program$n@@include $f";; -[W-]file) program="$program$n@@include ${2?'missing operand'}" shift;; -[W-]source=*) t=`expr "$1" : '-.source=\(.*\)'` program="$program$n$t";; -[W-]source) program="$program$n${2?'missing operand'}" shift;; -[W-]version) echo igawk: version 2.0 1>&2 gawk --version exit 0 ;; -[W-]*) opts="$opts '$1'" ;; *) break;; esac shift done if [ -z "$program" ] then program=${1?'missing program'} shift fi # At this point, `program' has the program. d14175 10 a14184 10 The `awk' program to process `@@include' directives is stored in the shell variable `expand_prog'. Doing this keeps the shell script readable. The `awk' program reads through the user's program, one line at a time, using `getline' (*note Getline::). The input file names and `@@include' statements are managed using a stack. As each `@@include' is encountered, the current file name is "pushed" onto the stack and the file named in the `@@include' directive becomes the current file name. As each file is finished, the stack is "popped," and the previous input file becomes the current input file again. The process is started by making the original file the first one on the stack. d14186 2 a14187 9 The `pathto' function does the work of finding the full path to a file. It simulates `gawk''s behavior when searching the `AWKPATH' environment variable (*note AWKPATH Variable::). If a file name has a `/' in it, no path search is done. Otherwise, the file name is concatenated with the name of each directory in the path, and an attempt is made to open the generated file name. The only way to test if a file can be read in `awk' is to go ahead and try to read it with `getline'; this is what `pathto' does.(2) If the file can be read, it is closed and the file name is returned: d14189 2 a14190 17 expand_prog=' function pathto(file, i, t, junk) { if (index(file, "/") != 0) return file for (i = 1; i <= ndirs; i++) { t = (pathlist[i] "/" file) if ((getline junk < t) > 0) { # found it close(t) return t } } return "" } d14192 3 a14194 4 The main program is contained inside one `BEGIN' rule. The first thing it does is set up the `pathlist' array that `pathto' uses. After splitting the path on `:', null elements are replaced with `"."', which represents the current directory: d14196 2 a14197 7 BEGIN { path = ENVIRON["AWKPATH"] ndirs = split(path, pathlist, ":") for (i = 1; i <= ndirs; i++) { if (pathlist[i] == "") pathlist[i] = "." } d14199 2 a14200 12 The stack is initialized with `ARGV[1]', which will be `/dev/stdin'. The main loop comes next. Input lines are read in succession. Lines that do not start with `@@include' are printed verbatim. If the line does start with `@@include', the file name is in `$2'. `pathto' is called to generate the full path. If it cannot, then we print an error message and continue. The next thing to check is if the file is included already. The `processed' array is indexed by the full file name of each included file and it tracks this information for us. If the file is seen again, a warning message is printed. Otherwise, the new file name is pushed onto the stack and processing continues. d14202 11 a14212 3 Finally, when `getline' encounters the end of the input file, the file is closed and the stack is popped. When `stackptr' is less than zero, the program is done: d14214 3 a14216 31 stackptr = 0 input[stackptr] = ARGV[1] # ARGV[1] is first file for (; stackptr >= 0; stackptr--) { while ((getline < input[stackptr]) > 0) { if (tolower($1) != "@@include") { print continue } fpath = pathto($2) if (fpath == "") { printf("igawk:%s:%d: cannot find %s\n", input[stackptr], FNR, $2) > "/dev/stderr" continue } if (! (fpath in processed)) { processed[fpath] = input[stackptr] input[++stackptr] = fpath # push onto stack } else print $2, "included in", input[stackptr], "already included in", processed[fpath] > "/dev/stderr" } close(input[stackptr]) } }' # close quote ends `expand_prog' variable processed_program=`gawk -- "$expand_prog" /dev/stdin < URL: `http://www.gnu.org' d15215 2 a15216 2 * Retrieve `gawk' by using anonymous `ftp' to the Internet host `ftp.gnu.org', in the directory `/gnu/gawk'. d15218 58 a15275 5 The GNU software archive is mirrored around the world. The up-to-date list of mirror sites is available from the main FSF web site (http://www.gnu.org/order/ftp.html). Try to use one of the mirrors; they will be less busy, and you can usually find one closer to your site. d15286 3 a15288 3 Once you have the distribution (for example, `gawk-3.1.3.tar.gz'), use `gzip' to expand the file and then use `tar' to extract it. You can use the following pipeline to produce the `gawk' distribution: d15290 2 a15291 2 # Under System V, add 'o' to the tar options gzip -d -c gawk-3.1.3.tar.gz | tar -xvpf - d15293 2 a15294 1 This creates a directory named `gawk-3.1.3' in the current directory. d15296 1 a15296 1 The distribution file name is of the form `gawk-V.R.P.tar.gz'. The d15298 1 a15298 1 release of version V, and the P represents a "patch level", meaning d15301 8 a15308 6 version with the highest version, release, and patch level. (Note, however, that patch levels greater than or equal to 80 denote "beta" or nonproduction software; you might not want to retrieve such a version unless you don't mind experimenting.) If you are not on a Unix system, you need to make other arrangements for getting and extracting the `gawk' distribution. You should consult a local expert. d15317 4 a15320 3 documentation files, subdirectories, and files related to the configuration process (*note Unix Installation::), as well as several subdirectories related to different non-Unix operating systems: d15322 2 a15323 2 Various `.c', `.y', and `.h' files The actual `gawk' source code. d15327 2 a15328 2 Descriptive files: `README' for `gawk' under Unix and the rest for the various hardware and software combinations. d15334 8 d15353 3 a15355 3 A brief list of features and changes being contemplated for future releases, with some indication of the time frame for the feature, based on its difficulty. d15359 1 a15359 1 these depend on the hardware or operating system software and are d15363 5 a15367 2 A description of one area in which the POSIX standard for `awk' is incorrect as well as how `gawk' handles the problem. d15382 1 a15382 1 modern version of `troff' such as GNU `troff' (`groff') is needed d15393 1 a15393 1 `makeinfo' to produce an Info or HTML file. a15397 8 `doc/gawkinet.texi' The Texinfo source file for *Note Top::. It should be processed with TeX to produce a printed document and with `makeinfo' to produce an Info or HTML file. `doc/gawkinet.info' The generated Info file for `TCP/IP Internetworking with `gawk''. d15400 2 a15401 1 program presented in *Note Igawk Program::. a15406 5 `Makefile.am' `*/Makefile.am' Files used by the GNU `automake' software for generating the `Makefile.in' files used by `autoconf' and `configure'. a15408 1 `acinclude.m4' d15414 4 a15417 11 `missing_d/*' `m4/*' These files and subdirectories are used when configuring `gawk' for various Unix systems. They are explained in *Note Unix Installation::. `intl/*' `po/*' The `intl' directory provides the GNU `gettext' library, which implements `gawk''s internationalization features, while the `po' library contains message translations. a15419 1 `awklib/Makefile.am' a15420 1 `awklib/eg/*' d15422 13 a15434 21 Extract Program::), which can be used to extract the sample programs from the Texinfo source file for this Info file. It also contains a `Makefile.in' file, which `configure' uses to generate a `Makefile'. `Makefile.am' is used by GNU Automake to create `Makefile.in'. The library functions from *Note Library Functions::, and the `igawk' program from *Note Igawk Program::, are included as ready-to-use files in the `gawk' distribution. They are installed as part of the installation process. The rest of the programs in this Info file are available in appropriate subdirectories of `awklib/eg'. `unsupported/atari/*' Files needed for building `gawk' on an Atari ST (*note Atari Installation::, for details). `unsupported/tandem/*' Files needed for building `gawk' on a Tandem (*note Tandem Installation::, for details). `posix/*' Files needed for building `gawk' on POSIX-compliant systems. d15437 3 a15439 2 Files needed for building `gawk' under MS-DOS, MS Windows and OS/2 (*note PC Installation::, for details). d15442 2 a15443 2 Files needed for building `gawk' under VMS (*note VMS Installation::, for details). d15446 4 a15449 4 A test suite for `gawk'. You can use `make check' from the top-level `gawk' directory to run your version of `gawk' against the test suite. If `gawk' successfully passes `make check', then you can be confident of a successful port. d15452 1 a15452 1 File: gawk.info, Node: Unix Installation, Next: Non-Unix Installation, Prev: Gawk Distribution, Up: Installation d15458 1 a15458 1 commands. However, if you use an unusual system, you may need to d15463 2 a15464 3 * Quick Installation:: Compiling `gawk' under Unix. * Additional Configuration Options:: Other compile-time options. * Configuration Philosophy:: How it's all supposed to work. d15467 1 a15467 1 File: gawk.info, Node: Quick Installation, Next: Additional Configuration Options, Up: Unix Installation d15473 1 a15473 1 `gawk-3.1.3'. Like most GNU software, `gawk' is configured d15475 1 a15475 1 This program is a Bourne shell script that is generated automatically d15477 1 a15477 1 starting with *Note Top::.) d15484 4 a15487 4 The `config.h' file describes various facts about your system. You might want to edit the `Makefile' to change the `CFLAGS' variable, which controls the command-line options that are passed to the C compiler (such as optimization levels or compiling for debugging). d15489 2 a15490 2 Alternatively, you can add your own values for most `make' variables on the command line, such as `CC' and `CFLAGS', when running d15497 1 a15497 1 After you have run `configure' and possibly edited the `Makefile', d15502 3 a15504 51 Shortly thereafter, you should have an executable version of `gawk'. That's all there is to it! To verify that `gawk' is working properly, run `make check'. All of the tests should succeed. If these steps do not work, or if any of the tests fail, check the files in the `README_d' directory to see if you've found a known problem. If the failure is not described there, please send in a bug report (*note Bugs::.)  File: gawk.info, Node: Additional Configuration Options, Next: Configuration Philosophy, Prev: Quick Installation, Up: Unix Installation Additional Configuration Options -------------------------------- There are several additional options you may use on the `configure' command line when compiling `gawk' from scratch, including: `--enable-portals' Treat pathnames that begin with `/p' as BSD portal files when doing two-way I/O with the `|&' operator (*note Portal Files::). `--enable-switch' Enable the recognition and execution of C-style `switch' statements in `awk' programs (*note Switch Statement::.) `--with-included-gettext' Use the version of the `gettext' library that comes with `gawk'. This option should be used on systems that do _not_ use version 2 (or later) of the GNU C library. All known modern GNU/Linux systems use Glibc 2. Use this option on any other system. `--disable-lint' This option disables all lint checking within `gawk'. The `--lint' and `--lint-old' options (*note Options::) are accepted, but silently do nothing. Similarly, setting the `LINT' variable (*note User-modified::) has no effect on the running `awk' program. When used with GCC's automatic dead-code-elimination, this option cuts almost 200K bytes off the size of the `gawk' executable on GNU/Linux x86 systems. Results on other systems and with other compilers are likely to vary. Using this option may bring you some slight performance improvement. Using this option will cause some of the tests in the test suite to fail. This option may be removed at a later date. `--disable-nls' Disable all message-translation facilities. This is usually not desirable, but it may bring you some slight performance improvement. You should also use this option if `--with-included-gettext' doesn't work on your system. d15507 1 a15507 1 File: gawk.info, Node: Configuration Philosophy, Prev: Additional Configuration Options, Up: Unix Installation d15512 2 a15513 2 This minor node is of interest only if you know something about using the C language and the Unix operating system. d15517 2 a15518 2 routines that are specified by the ISO C standard and by the POSIX operating system interface standard. When using an ISO C compiler, d15521 3 a15523 3 Many Unix systems do not support all of either the ISO or the POSIX standards. The `missing_d' subdirectory in the `gawk' distribution contains replacement versions of those functions that are most likely d15526 9 a15534 8 The `config.h' file that `configure' creates contains definitions that describe features of the particular operating system where you are attempting to compile `gawk'. The three things described by this file are: what header files are available, so that they can be correctly included, what (supposedly) standard functions are actually available in your C libraries, and various miscellaneous facts about your variant of Unix. For example, there may not be an `st_blksize' element in the `stat' structure. In this case, `HAVE_ST_BLKSIZE' is undefined. d15538 5 a15542 5 available. To get around this, edit the file `custom.h'. Use an `#ifdef' that is appropriate for your system, and either `#define' any constants that `configure' should have defined but didn't, or `#undef' any constants that `configure' defined and should not have. `custom.h' is automatically included by `config.h'. d15547 5 a15551 434 You may be able to change this file and generate a new version of `configure' that works on your system (*note Bugs::, for information on how to report problems in configuring `gawk'). The same mechanism may be used to send in updates to `configure.in' and/or `custom.h'.  File: gawk.info, Node: Non-Unix Installation, Next: Unsupported, Prev: Unix Installation, Up: Installation Installation on Other Operating Systems ======================================= This minor node describes how to install `gawk' on various non-Unix systems. * Menu: * Amiga Installation:: Installing `gawk' on an Amiga. * BeOS Installation:: Installing `gawk' on BeOS. * PC Installation:: Installing and Compiling `gawk' on MS-DOS and OS/2. * VMS Installation:: Installing `gawk' on VMS.  File: gawk.info, Node: Amiga Installation, Next: BeOS Installation, Up: Non-Unix Installation Installing `gawk' on an Amiga ----------------------------- You can install `gawk' on an Amiga system using a Unix emulation environment, available via anonymous `ftp' from `ftp.ninemoons.com' in the directory `pub/ade/current'. This includes a shell based on `pdksh'. The primary component of this environment is a Unix emulation library, `ixemul.lib'. A more complete distribution for the Amiga is available on the Geek Gadgets CD-ROM, available from: CRONUS 1840 E. Warner Road #105-265 Tempe, AZ 85284 USA US Toll Free: (800) 804-0833 Phone: +1-602-491-0442 FAX: +1-602-491-0048 Email: WWW: `http://www.ninemoons.com' Anonymous `ftp' site: `ftp.ninemoons.com' Once you have the distribution, you can configure `gawk' simply by running `configure': configure -v m68k-amigaos Then run `make' and you should be all set! If these steps do not work, please send in a bug report (*note Bugs::).  File: gawk.info, Node: BeOS Installation, Next: PC Installation, Prev: Amiga Installation, Up: Non-Unix Installation Installing `gawk' on BeOS ------------------------- Since BeOS DR9, all the tools that you should need to build `gawk' are included with BeOS. The process is basically identical to the Unix process of running `configure' and then `make'. Full instructions are given below. You can compile `gawk' under BeOS by extracting the standard sources and running `configure'. You _must_ specify the location prefix for the installation directory. For BeOS DR9 and beyond, the best directory to use is `/boot/home/config', so the `configure' command is: configure --prefix=/boot/home/config This installs the compiled application into `/boot/home/config/bin', which is already specified in the standard `PATH'. Once the configuration process is completed, you can run `make', and then `make install': $ make ... $ make install BeOS uses `bash' as its shell; thus, you use `gawk' the same way you would under Unix. If these steps do not work, please send in a bug report (*note Bugs::).  File: gawk.info, Node: PC Installation, Next: VMS Installation, Prev: BeOS Installation, Up: Non-Unix Installation Installation on PC Operating Systems ------------------------------------ This minor node covers installation and usage of `gawk' on x86 machines running DOS, any version of Windows, or OS/2. In this minor node, the term "Windows32" refers to any of Windows-95/98/ME/NT/2000. The limitations of DOS (and DOS shells under Windows or OS/2) has meant that various "DOS extenders" are often used with programs such as `gawk'. The varying capabilities of Microsoft Windows 3.1 and Windows32 can add to the confusion. For an overview of the considerations, please refer to `README_d/README.pc' in the distribution. * Menu: * PC Binary Installation:: Installing a prepared distribution. * PC Compiling:: Compiling `gawk' for MS-DOS, Windows32, and OS/2. * PC Dynamic:: Compiling `gawk' for dynamic libraries. * PC Using:: Running `gawk' on MS-DOS, Windows32 and OS/2. * Cygwin:: Building and running `gawk' for Cygwin.  File: gawk.info, Node: PC Binary Installation, Next: PC Compiling, Up: PC Installation Installing a Prepared Distribution for PC Systems ................................................. If you have received a binary distribution prepared by the DOS maintainers, then `gawk' and the necessary support files appear under the `gnu' directory, with executables in `gnu/bin', libraries in `gnu/lib/awk', and manual pages under `gnu/man'. This is designed for easy installation to a `/gnu' directory on your drive--however, the files can be installed anywhere provided `AWKPATH' is set properly. Regardless of the installation directory, the first line of `igawk.cmd' and `igawk.bat' (in `gnu/bin') may need to be edited. The binary distribution contains a separate file describing the contents. In particular, it may include more than one version of the `gawk' executable. OS/2 (32 bit, EMX) binary distributions are prepared for the `/usr' directory of your preferred drive. Set `UNIXROOT' to your installation drive (e.g., `e:') if you want to install `gawk' onto another drive than the hardcoded default `c:'. Executables appear in `/usr/bin', libraries under `/usr/share/awk', manual pages under `/usr/man', Texinfo documentation under `/usr/info' and NLS files under `/usr/share/locale'. If you already have a file `/usr/info/dir' from another package _do not overwrite it!_ Instead enter the following commands at your prompt (replace `x:' by your installation drive): install-info --info-dir=x:/usr/info x:/usr/info/gawk.info install-info --info-dir=x:/usr/info x:/usr/info/gawkinet.info However, the files can be installed anywhere provided `AWKPATH' is set properly. The binary distribution may contain a separate file containing additional or more detailed installation instructions.  File: gawk.info, Node: PC Compiling, Next: PC Dynamic, Prev: PC Binary Installation, Up: PC Installation Compiling `gawk' for PC Operating Systems ......................................... `gawk' can be compiled for MS-DOS, Windows32, and OS/2 using the GNU development tools from DJ Delorie (DJGPP; MS-DOS only) or Eberhard Mattes (EMX; MS-DOS, Windows32 and OS/2). Microsoft Visual C/C++ can be used to build a Windows32 version, and Microsoft C/C++ can be used to build 16-bit versions for MS-DOS and OS/2. (As of `gawk' 3.1.2, the MSC version doesn't work. However, the maintainer is working on fixing it.) The file `README_d/README.pc' in the `gawk' distribution contains additional notes, and `pc/Makefile' contains important information on compilation options. To build `gawk' for MS-DOS, Windows32, and OS/2 (16 bit only; for 32 bit (EMX) you can use the `configure' script and skip the following paragraphs; for details see below), copy the files in the `pc' directory (_except_ for `ChangeLog') to the directory with the rest of the `gawk' sources. The `Makefile' contains a configuration section with comments and may need to be edited in order to work with your `make' utility. The `Makefile' contains a number of targets for building various MS-DOS, Windows32, and OS/2 versions. A list of targets is printed if the `make' command is given without a target. As an example, to build `gawk' using the DJGPP tools, enter `make djgpp'. Using `make' to run the standard tests and to install `gawk' requires additional Unix-like tools, including `sh', `sed', and `cp'. In order to run the tests, the `test/*.ok' files may need to be converted so that they have the usual DOS-style end-of-line markers. Most of the tests work properly with Stewartson's shell along with the companion utilities or appropriate GNU utilities. However, some editing of `test/Makefile' is required. It is recommended that you copy the file `pc/Makefile.tst' over the file `test/Makefile' as a replacement. Details can be found in `README_d/README.pc' and in the file `pc/Makefile.tst'. The 32 bit EMX version of `gawk' works "out of the box" under OS/2. In principle, it is possible to compile `gawk' the following way: $ ./configure $ make This is not recommended, though. To get an OMF executable you should use the following commands at your `sh' prompt: $ CPPFLAGS="-D__ST_MT_ERRNO__" $ export CPPFLAGS $ CFLAGS="-O2 -Zomf -Zmt" $ export CFLAGS $ LDFLAGS="-s -Zcrtdll -Zlinker /exepack:2 -Zlinker /pm:vio -Zstack 0x8000" $ export LDFLAGS $ RANLIB="echo" $ export RANLIB $ ./configure --prefix=c:/usr --without-included-gettext $ make AR=emxomfar These are just suggestions. You may use any other set of (self-consistent) environment variables and compiler flags. To get an FHS-compliant file hierarchy it is recommended to use the additional `configure' options `--infodir=c:/usr/share/info', `--mandir=c:/usr/share/man' and `--libexecdir=c:/usr/lib'. The internal `gettext' library tends to be problematic. It is therefore recommended to use either an external one (`--without-included-gettext') or to disable NLS entirely (`--disable-nls'). If you use GCC 2.95 or newer it is recommended to use also: $ LIBS="-lgcc" $ export LIBS You can also get an `a.out' executable if you prefer: $ CPPFLAGS="-D__ST_MT_ERRNO__" $ export CPPFLAGS $ CFLAGS="-O2 -Zmt" $ export CFLAGS $ LDFLAGS="-s -Zstack 0x8000" $ LIBS="-lgcc" $ unset RANLIB $ ./configure --prefix=c:/usr --without-included-gettext $ make *Note:* Even if the compiled `gawk.exe' (`a.out') executable contains a DOS header, it does _not_ work under DOS. To compile an executable that runs under DOS, `"-DPIPES_SIMULATED"' must be added to `CPPFLAGS'. But then some nonstandard extensions of `gawk' (e.g., `|&') do not work! After compilation the internal tests can be performed. Enter `make check CMP="diff -a"' at your command prompt. All tests but the `pid' test are expected to work properly. The `pid' test fails because child processes are not started by `fork()'. `make install' works as expected. *Note:* Most OS/2 ports of GNU `make' are not able to handle the Makefiles of this package. If you encounter any problems with `make' try GNU Make 3.79.1 or later versions. You should find the latest version on `http://www.unixos2.org/sw/pub/binary/make/' or on `ftp://hobbes.nmsu.edu/pub/os2/'.  File: gawk.info, Node: PC Dynamic, Next: PC Using, Prev: PC Compiling, Up: PC Installation Compiling `gawk' For Dynamic Libraries ...................................... To compile `gawk' with dynamic extension support, uncomment the definitions of `DYN_FLAGS', `DYN_EXP', `DYN_OBJ', and `DYN_MAKEXP' in the configuration section of the `Makefile'. There are two definitions for `DYN_MAKEXP': pick the one that matches your target. To build some of the example extension libraries, `cd' to the extension directory and copy `Makefile.pc' to `Makefile'. You can then build using the same two targets. To run the example `awk' scripts, you'll need to either change the call to the `extension' function to match the name of the library (for instance, change `"./ordchr.so"' to `"ordchr.dll"' or simply `"ordchr"'), or rename the library to match the call (for instance, rename `ordchr.dll' to `ordchr.so'). If you build `gawk.exe' with one compiler but want to build an extension library with the other, you need to copy the import library. Visual C uses a library called `gawk.lib', while MinGW uses a library called `libgawk.a'. These files are equivalent and will interoperate if you give them the correct name. The resulting shared libraries are also interoperable. To create your own extension library, you can use the examples as models, but you're essentially on your own. Post to `comp.lang.awk' or send electronic mail to if you have problems getting started. If you need to access functions or variables which are not exported by `gawk.exe', add them to `gawkw32.def' and rebuild. You should also add `ATTRIBUTE_EXPORTED' to the declaration in `awk.h' of any variables you add to `gawkw32.def'. Note that extension libraries have the name of the `awk' executable embedded in them at link time, so they will work only with `gawk.exe'. In particular, they won't work if you rename `gawk.exe' to `awk.exe' or if you try to use `pgawk.exe'. You can perform profiling by temporarily renaming `pgawk.exe' to `gawk.exe'. You can resolve this problem by changing the program name in the definition of `DYN_MAKEXP' for your compiler. On Windows32, libraries are sought first in the current directory, then in the directory containing `gawk.exe', and finally through the `PATH' environment variable.  File: gawk.info, Node: PC Using, Next: Cygwin, Prev: PC Dynamic, Up: PC Installation Using `gawk' on PC Operating Systems .................................... With the exception of the Cygwin environment, the `|&' operator and TCP/IP networking (*note TCP/IP Networking::) are not supported for MS-DOS or MS-Windows. EMX (OS/2 only) does support at least the `|&' operator. The OS/2 and MS-DOS versions of `gawk' search for program files as described in *Note AWKPATH Variable::. However, semicolons (rather than colons) separate elements in the `AWKPATH' variable. If `AWKPATH' is not set or is empty, then the default search path for OS/2 (16 bit) and MS-DOS versions is `".;c:/lib/awk;c:/gnu/lib/awk"'. The search path for OS/2 (32 bit, EMX) is determined by the prefix directory (most likely `/usr' or `c:/usr') that has been specified as an option of the `configure' script like it is the case for the Unix versions. If `c:/usr' is the prefix directory then the default search path contains `.' and `c:/usr/share/awk'. Additionally, to support binary distributions of `gawk' for OS/2 systems whose drive `c:' might not support long file names or might not exist at all, there is a special environment variable. If `UNIXROOT' specifies a drive then this specific drive is also searched for program files. E.g., if `UNIXROOT' is set to `e:' the complete default search path is `".;c:/usr/share/awk;e:/usr/share/awk"'. An `sh'-like shell (as opposed to `command.com' under MS-DOS or `cmd.exe' under OS/2) may be useful for `awk' programming. Ian Stewartson has written an excellent shell for MS-DOS and OS/2, Daisuke Aoyama has ported GNU `bash' to MS-DOS using the DJGPP tools, and several shells are available for OS/2, including `ksh'. The file `README_d/README.pc' in the `gawk' distribution contains information on these shells. Users of Stewartson's shell on DOS should examine its documentation for handling command lines; in particular, the setting for `gawk' in the shell configuration may need to be changed and the `ignoretype' option may also be of interest. Under OS/2 and DOS, `gawk' (and many other text programs) silently translate end-of-line `"\r\n"' to `"\n"' on input and `"\n"' to `"\r\n"' on output. A special `BINMODE' variable allows control over these translations and is interpreted as follows: * If `BINMODE' is `"r"', or `(BINMODE & 1)' is nonzero, then binary mode is set on read (i.e., no translations on reads). * If `BINMODE' is `"w"', or `(BINMODE & 2)' is nonzero, then binary mode is set on write (i.e., no translations on writes). * If `BINMODE' is `"rw"' or `"wr"', binary mode is set for both read and write (same as `(BINMODE & 3)'). * `BINMODE=NON-NULL-STRING' is the same as `BINMODE=3' (i.e., no translations on reads or writes). However, `gawk' issues a warning message if the string is not one of `"rw"' or `"wr"'. The modes for standard input and standard output are set one time only (after the command line is read, but before processing any of the `awk' program). Setting `BINMODE' for standard input or standard output is accomplished by using an appropriate `-v BINMODE=N' option on the command line. `BINMODE' is set at the time a file or pipe is opened and cannot be changed mid-stream. The name `BINMODE' was chosen to match `mawk' (*note Other Versions::). Both `mawk' and `gawk' handle `BINMODE' similarly; however, `mawk' adds a `-W BINMODE=N' option and an environment variable that can set `BINMODE', `RS', and `ORS'. The files `binmode[1-3].awk' (under `gnu/lib/awk' in some of the prepared distributions) have been chosen to match `mawk''s `-W BINMODE=N' option. These can be changed or discarded; in particular, the setting of `RS' giving the fewest "surprises" is open to debate. `mawk' uses `RS = "\r\n"' if binary mode is set on read, which is appropriate for files with the DOS-style end-of-line. To illustrate, the following examples set binary mode on writes for standard output and other files, and set `ORS' as the "usual" DOS-style end-of-line: gawk -v BINMODE=2 -v ORS="\r\n" ... or: gawk -v BINMODE=w -f binmode2.awk ... These give the same result as the `-W BINMODE=2' option in `mawk'. The following changes the record separator to `"\r\n"' and sets binary mode on reads, but does not affect the mode on standard input: gawk -v RS="\r\n" --source "BEGIN { BINMODE = 1 }" ... or: gawk -f binmode1.awk ... With proper quoting, in the first example the setting of `RS' can be moved into the `BEGIN' rule.  File: gawk.info, Node: Cygwin, Prev: PC Using, Up: PC Installation Using `gawk' In The Cygwin Environment ...................................... `gawk' can be used "out of the box" under Windows if you are using the Cygwin environment.(1) This environment provides an excellent simulation of Unix, using the GNU tools, such as `bash', the GNU Compiler Collection (GCC), GNU Make, and other GNU tools. Compilation and installation for Cygwin is the same as for a Unix system: tar -xvpzf gawk-3.1.3.tar.gz cd gawk-3.1.3 ./configure make When compared to GNU/Linux on the same system, the `configure' step on Cygwin takes considerably longer. However, it does finish, and then the `make' proceeds as usual. *Note:* The `|&' operator and TCP/IP networking (*note TCP/IP Networking::) are fully supported in the Cygwin environment. This is not true for any other environment for MS-DOS or MS-Windows. ---------- Footnotes ---------- (1) `http://www.cygwin.com' d15554 1 a15554 1 File: gawk.info, Node: VMS Installation, Prev: PC Installation, Up: Non-Unix Installation d15557 1 a15557 1 ---------------------------------------- d15559 1 a15559 1 This node describes how to compile and install `gawk' under VMS. d15569 1 a15569 1 File: gawk.info, Node: VMS Compilation, Next: VMS Installation Details, Up: VMS Installation d15572 1 a15572 1 ....................... d15575 3 a15577 3 issues all the necessary `CC' and `LINK' commands. There is also a `Makefile' for use with the `MMS' utility. From the source directory, use either: d15581 1 a15581 1 or: d15602 2 a15603 2 from those for VAX C V2.x but equally straightforward. No changes to `config.h' are needed. d15607 1 a15607 1 No changes to `config.h' are needed. d15609 2 a15610 3 `gawk' has been tested under VAX/VMS 5.5-1 using VAX C V3.2, and GNU C 1.40 and 2.3. It should work without modifications for VMS V4.6 and up. d15616 1 a15616 1 ........................ d15623 3 a15625 3 Substitute the actual location of `gawk.exe' for `$disk1:[gnubin]'. The symbol should be placed in the `login.com' of any user who wants to run `gawk', so that it is defined every time the user logs on. d15627 1 a15627 1 `sylogin.com' procedure, which allows all users to run `gawk'. d15634 1 a15634 2 the standard VMS library `HELPLIB'.) After loading the help text, the command: d15638 2 a15639 2 provides information about both the `gawk' implementation and the `awk' programming language. d15642 8 a15649 8 `awk' program files. For the `-f' option, if the specified file name has no device or directory path information in it, `gawk' looks in the current directory first, then in the directory specified by the translation of `AWK_LIBRARY' if the file is not found. If, after searching in both directories, the file still is not found, `gawk' appends the suffix `.awk' to the filename and retries the file search. If `AWK_LIBRARY' is not defined, that portion of the file search fails benignly. d15655 1 a15655 1 ..................... d15657 1 a15657 1 Command-line parsing and quoting conventions are significantly d15659 1 a15659 1 often need minor changes. They _are_ minor though, and all `awk' d15668 1 a15668 1 Note that uppercase and mixed-case text must be quoted. d15672 1 a15672 1 One side effect of dual command-line parsing is that if there is only a d15676 2 a15677 2 other dash-type options (or multiple parameters such as data files to process) are present, there is no ambiguity and `--' can be omitted. d15679 2 a15680 2 The default search path, when looking for `awk' program files specified by the `-f' option, is `"SYS$DISK:[],AWK_LIBRARY:"'. The d15684 1 a15684 1 translation and not a multitranslation `RMS' searchlist. d15690 1 a15690 1 ...................................... d15694 2 a15695 2 into a container file subsystem rather than into the ordinary VMS filesystem. Make sure that the two scripts, `configure' and d15702 1 a15702 1 The first command constructs files `config.h' and `Makefile' out of d15704 4 a15707 4 expectations. The second command compiles and links `gawk' using the C compiler directly; ignore any warnings from `make' about being unable to redefine `CC'. `configure' takes a very long time to execute, but at least it provides incremental feedback as it runs. d15712 2 a15713 2 Once built, `gawk' works like any other shell utility. Unlike the normal VMS port of `gawk', no special command-line manipulation is d15717 24 a15740 1 File: gawk.info, Node: Unsupported, Next: Bugs, Prev: Non-Unix Installation, Up: Installation d15742 9 a15750 2 Unsupported Operating System Ports ================================== d15752 11 a15762 2 This sections describes systems for which the `gawk' port is no longer supported. d15764 4 a15767 1 * Menu: d15769 9 a15777 2 * Atari Installation:: Installing `gawk' on the Atari ST. * Tandem Installation:: Installing `gawk' on a Tandem. d15780 1 a15780 1 File: gawk.info, Node: Atari Installation, Next: Tandem Installation, Up: Unsupported d15783 1 a15783 4 --------------------------------- The Atari port is no longer supported. It is included for those who might want to use it but it is no longer being actively maintained. d15787 2 a15788 2 large amount of memory with most `awk' programs, and should run on all Motorola processor-based models (called further ST, even if that is not d15793 7 a15799 7 uppercase. Maintaining case distinction in option flags is very important (*note Options::). These days this is the default and it may only be a problem for some very old machines. If your system does not preserve the case of option flags, you need to upgrade your tools. Support for I/O redirection is necessary to make it easy to import `awk' programs from other environments. Pipes are nice to have but not vital. d15803 2 a15804 2 * Atari Compiling:: Compiling `gawk' on Atari. * Atari Using:: Running `gawk' on Atari. d15807 1 a15807 1 File: gawk.info, Node: Atari Compiling, Next: Atari Using, Up: Atari Installation d15810 1 a15810 1 ................................ d15813 1 a15813 1 from `sizeof(void *)' requires an ISO C compiler. An initial port was d15815 1 a15815 1 four bytes wide but the other variant works as well. d15820 1 a15820 1 optimization level for this particular file, which may help. d15822 8 a15829 8 With a reasonable shell (`bash' will do), you have a pretty good chance that the `configure' utility will succeed, and in particular if you run GNU/Linux, MiNT or a similar operating system. Otherwise sample versions of `config.h' and `Makefile.st' are given in the `atari' subdirectory and can be edited and copied to the corresponding files in the main source directory. Even if `configure' produces something, it might be advisable to compare its results with the sample versions and possibly make adjustments. d15835 1 a15835 1 *Note Atari Using::. d15839 4 a15842 4 implementation of this function is provided in `unsupported/atari/system.c'. Depending upon your particular combination of shell and operating system, you might want to change the file to indicate that `system' is available. d15848 1 a15848 1 .............................. d15853 20 a15872 21 While executing, the Atari version of `gawk' creates a number of temporary files. When using `gcc' libraries for TOS, `gawk' looks for either of the environment variables, `TEMP' or `TMPDIR', in that order. If either one is found, its value is assumed to be a directory for temporary files. This directory must exist, and if you can spare the memory, it is a good idea to put it on a RAM drive. If neither `TEMP' nor `TMPDIR' are found, then `gawk' uses the current directory for its temporary files. The ST version of `gawk' searches for its program files, as described in *Note AWKPATH Variable::. The default value for the `AWKPATH' variable is taken from `DEFPATH' defined in `Makefile'. The sample `gcc'/TOS `Makefile' for the ST in the distribution sets `DEFPATH' to `".,c:\lib\awk,c:\gnu\lib\awk"'. The search path can be modified by explicitly setting `AWKPATH' to whatever you want. Note that colons cannot be used on the ST to separate elements in the `AWKPATH' variable, since they have another reserved meaning. Instead, you must use a comma to separate elements in the path. When recompiling, the separating character can be modified by initializing the `envsep' variable in `unsupported/atari/gawkmisc.atr' to another value. d15876 4 a15879 4 running under TOS. In some circumstances, the OS routines for file-handle pool processing lose track of certain events, causing the computer to crash and requiring a reboot. Often a warm reboot is sufficient. Fortunately, this happens infrequently and in rather d15882 3 a15884 2 `/dev/stdout', while other `print' statements use the default standard output, and a calling shell has redirected standard output to a file. d15887 9 a15895 9 libraries, it accepts both `/' and `\' as path separators. While this is convenient, it should be remembered that this removes one technically valid character (`/') from your file name. It may also create problems for external programs called via the `system' function, which may not support this convention. Whenever it is possible that a file created by `gawk' will be used by some other program, use only backslashes. Also remember that in `awk', backslashes in strings have to be doubled in order to get literal backslashes (*note Escape Sequences::). d15898 23 a15920 1 File: gawk.info, Node: Tandem Installation, Prev: Atari Installation, Up: Unsupported d15922 2 a15923 2 Installing `gawk' on a Tandem ----------------------------- d15925 1 a15925 2 The Tandem port is only minimally supported. The port's contributor no longer has access to a Tandem system. d15927 3 a15929 27 The Tandem port was done on a Cyclone machine running D20. The port is pretty clean and all facilities seem to work except for the I/O piping facilities (*note Getline/Pipe::, *Note Getline/Variable/Pipe::, and *Note Redirection::), which is just too foreign a concept for Tandem. To build a Tandem executable from source, download all of the files so that the file names on the Tandem box conform to the restrictions of D20. For example, `array.c' becomes `ARRAYC', and `awk.h' becomes `AWKH'. The totally Tandem-specific files are in the `tandem' "subvolume" (`unsupported/tandem' in the `gawk' distribution) and should be copied to the main source directory before building `gawk'. The file `compit' can then be used to compile and bind an executable. Alas, there is no `configure' or `make'. Usage is the same as for Unix, except that D20 requires all `{' and `}' characters to be escaped with `~' on the command line (but _not_ in script files). Also, the standard Tandem syntax for `/in filename,out filename/' must be used instead of the usual Unix `<' and `>' for file redirection. (Redirection options on `getline', `print' etc., are supported.) The `-mr VAL' option (*note Options::) has been "stolen" to enable Tandem users to process fixed-length records with no "end-of-line" character. That is, `-mr 74' tells `gawk' to read the input file as fixed 74-byte records. d15932 1 a15932 1 File: gawk.info, Node: Bugs, Next: Other Versions, Prev: Unsupported, Up: Installation d15953 9 a15961 4 idea of what kind of Unix system you're using, the compiler you used to compile `gawk', and the exact results `gawk' gave you. Also say what you expected to occur; this helps us decide whether the problem is really in the documentation. d15963 2 a15964 1 Once you have a precise problem, send email to . d15967 3 a15969 6 get this information with the command `gawk --version'. Using this address automatically sends a carbon copy of your mail to me. If necessary, I can be reached directly at . The bug reporting address is preferred since the email list is archived at the GNU Project. _All email should be in English, since that is my native language._ d15971 1 a15971 1 *Caution:* Do _not_ try to report bugs in `gawk' by posting to the d15974 1 a15974 1 see your posting. The steps described above are the official d15977 5 a15981 72 Non-bug suggestions are always welcome as well. If you have questions about things that are unclear in the documentation or are just obscure features, ask me; I will try to help you out, although I may not have the time to fix the problem. You can send me electronic mail at the Internet address noted previously. If you find bugs in one of the non-Unix ports of `gawk', please send an electronic mail message to the person who maintains that port. They are named in the following list, as well as in the `README' file in the `gawk' distribution. Information in the `README' file should be considered authoritative if it conflicts with this Info file. The people maintaining the non-Unix ports of `gawk' are as follows: Amiga Fred Fish, . BeOS Martin Brown, . MS-DOS Scott Deifik, and Darrel Hankerson, . MS-Windows Juan Grigera, . OS/2 The Unix for OS/2 team, . Tandem Stephen Davies, . VMS Pat Rankin, . If your bug is also reproducible under Unix, please send a copy of your report to the email list as well.  File: gawk.info, Node: Other Versions, Prev: Bugs, Up: Installation Other Freely Available `awk' Implementations ============================================ It's kind of fun to put comments like this in your awk code. `// Do C++ comments work? answer: yes! of course' Michael Brennan There are three other freely available `awk' implementations. This minor node briefly describes where to get them: Unix `awk' Brian Kernighan has made his implementation of `awk' freely available. You can retrieve this version via the World Wide Web from his home page.(1) It is available in several archive formats: Shell archive `http://cm.bell-labs.com/who/bwk/awk.shar' Compressed `tar' file `http://cm.bell-labs.com/who/bwk/awk.tar.gz' Zip file `http://cm.bell-labs.com/who/bwk/awk.zip' This version requires an ISO C (1990 standard) compiler; the C compiler from GCC (the GNU Compiler Collection) works quite nicely. *Note BTL::, for a list of extensions in this `awk' that are not in POSIX `awk'. `mawk' Michael Brennan has written an independent implementation of `awk', called `mawk'. It is available under the GPL (*note Copying::), just as `gawk' is. You can get it via anonymous `ftp' to the host `ftp.whidbey.net'. Change directory to `/pub/brennan'. Use "binary" or "image" mode, and retrieve `mawk1.3.3.tar.gz' (or the latest version that is there). `gunzip' may be used to decompress this file. Installation is similar to `gawk''s (*note Unix Installation::). d15983 5 a15987 1 `mawk' has the following extensions that are not in POSIX `awk': d15989 1 a15989 2 * The `fflush' built-in function for flushing buffered output (*note I/O Functions::). d15991 3 a15993 2 * The `**' and `**=' operators (*note Arithmetic Ops:: and also see *Note Assignment Ops::). d15995 2 a15996 2 * The use of `func' as an abbreviation for `function' (*note Definition Syntax::). d15998 2 a15999 1 * The `\x' escape sequence (*note Escape Sequences::). d16001 2 a16002 3 * The `/dev/stdout', and `/dev/stderr' special files (*note Special Files::). Use `"-"' instead of `"/dev/stdin"' with `mawk'. d16004 2 a16005 2 * The ability for `FS' and for the third argument to `split' to be null strings (*note Single Character Fields::). d16007 3 a16009 2 * The ability to delete all of an array at once with `delete ARRAY' (*note Delete::). d16011 2 a16012 1 * The ability for `RS' to be a regexp (*note Records::). d16014 2 a16015 2 * The `BINMODE' special variable for non-Unix operating systems (*note PC Using::). d16017 3 a16019 1 The next version of `mawk' will support `nextfile'. d16021 2 a16022 5 `awka' Written by Andrew Sumner, `awka' translates `awk' programs into C, compiles them, and links them with a library of functions that provides the core `awk' functionality. It also has a number of extensions. d16024 9 a16032 2 The `awk' translator is released under the GPL, and the library is under the LGPL. d16034 2 a16035 2 To get `awka', go to `http://awka.sourceforge.net'. You can reach Andrew Sumner at . d16037 4 a16040 7 `pawk' Nelson H.F. Beebe at the University of Utah has modified the Bell Labs `awk' to provide timing and profiling information. It is different from `pgawk' (*note Profiling::), in that it uses CPU-based profiling, not line-count profiling. You may find it at either `ftp://ftp.math.utah.edu/pub/pawk/pawk-20020210.tar.gz' or `http://www.math.utah.edu/pub/pawk/pawk-20020210.tar.gz'. d16042 4 d16047 3 a16049 3 ---------- Footnotes ---------- (1) `http://cm.bell-labs.com/who/bwk' d16052 1 a16052 1 File: gawk.info, Node: Notes, Next: Basic Concepts, Prev: Installation, Up: Top d16059 1 a16059 1 specifically to `gawk' and not to other implementations. d16063 1 a16063 2 * Compatibility Mode:: How to disable certain `gawk' extensions. a16064 2 * Dynamic Extensions:: Adding new built-in functions to `gawk'. d16066 1 d16069 1 a16069 1 File: gawk.info, Node: Compatibility Mode, Next: Additions, Up: Notes d16074 4 a16077 4 *Note POSIX/GNU::, for a summary of the GNU extensions to the `awk' language and program. All of these features can be turned off by invoking `gawk' with the `--traditional' option or with the `--posix' option. d16084 1 a16084 1 Prints out the parse stack information as the program is being d16087 1 a16087 1 This option is intended only for serious `gawk' developers and not d16092 1 a16092 1 File: gawk.info, Node: Additions, Next: Dynamic Extensions, Prev: Compatibility Mode, Up: Notes d16097 1 a16097 1 If you find that you want to enhance `gawk' in a significant d16099 2 a16100 2 free software; the source code is available and you are free to change it as you want (*note Copying::). d16102 2 a16103 2 This minor node discusses the ways you might want to change `gawk' as well as any considerations you should bear in mind. d16107 2 a16108 4 * Adding Code:: Adding code to the main body of `gawk'. * New Ports:: Porting `gawk' to a new operating system. d16111 1 a16111 1 File: gawk.info, Node: Adding Code, Next: New Ports, Up: Additions d16119 1 a16119 6 make it possible for me to include your changes: 1. Before building the new feature into `gawk' itself, consider writing it as an extension module (*note Dynamic Extensions::). If that's not possible, continue with the rest of the steps in this list. d16121 1 a16121 1 2. Get the latest version. It is much easier for me to integrate d16124 3 a16126 2 not be able to integrate them at all. (*Note Getting::, for information on getting the latest version of `gawk'.) d16128 1 a16128 1 3. See *note (Version)Top:: standards, GNU Coding Standards. This d16130 3 a16132 7 haven't read it, please do so, preferably _before_ starting to modify `gawk'. (The `GNU Coding Standards' are available from the GNU Project's `ftp' site, at `ftp://ftp.gnu.org/gnu/GNUinfo/standards.text'. An HTML version, suitable for reading with a WWW browser, is available at `http://www.gnu.org/prep/standards_toc.html'. Texinfo, Info, and DVI versions are also available.) d16134 1 a16134 1 4. Use the `gawk' coding style. The C code for `gawk' follows the d16137 2 a16138 2 particularly as regards to the placement of braces and the use of tabs. In brief, the coding rules for `gawk' are as follows: d16140 1 a16140 1 * Use ANSI/ISO style (prototype) function headers when defining d16149 3 d16153 1 a16153 1 (`if', `while', `for', `do', `switch', and `return'). d16158 1 a16158 1 * Put spaces around all C operators and after commas in d16161 3 a16163 3 * Do not use the comma operator to produce multiple side effects, except in `for' loop initialization and increment parts, and in macro bodies. d16170 2 a16171 2 `if', `while', and `for' statements, as well as in the `case's of `switch' statements, instead of just the plain pointer or d16174 3 a16176 7 * Use the `TRUE', `FALSE' and `NULL' symbolic constants and the character constant `'\0'' where appropriate, instead of `1' and `0'. * Use the `ISALPHA', `ISDIGIT', etc. macros, instead of the traditional lowercase versions; these macros are better behaved for non-ASCII character sets. d16184 3 a16186 3 the stack. Its use causes more portability trouble than is worth the minor benefit of not having to free the storage. Instead, use `malloc' and `free'. d16188 2 a16189 2 *Note:* If I have to reformat your code to follow the coding style used in `gawk', I may not bother to integrate your changes at all. d16191 1 a16191 1 5. Be prepared to sign the appropriate paperwork. In order for the d16193 1 a16193 1 changes in the public domain and submit a signed statement to that d16195 3 a16197 3 of these actions are easy to do and _many_ people have done so already. If you have questions, please contact me (*note Bugs::), or . d16199 2 a16200 2 6. Update the documentation. Along with your new code, please supply new sections and/or chapters for this Info file. If at all d16203 4 a16206 4 documentation at all). Conventions to be followed in `GAWK: Effective AWK Programming' are provided after the `@@bye' at the end of the Texinfo source file. If possible, please update the `man' page as well. d16211 1 a16211 1 7. Submit changes as context diffs or unified diffs. Use `diff -c -r d16213 5 a16217 5 with your version. (I find context diffs to be more readable but unified diffs are more compact.) I recommend using the GNU version of `diff'. Send the output produced by either run of `diff' to me when you submit your changes. (*Note Bugs::, for the electronic mail information.) a16223 4 8. Include an entry for the `ChangeLog' file with your submission. This helps further minimize the amount of work I have to do, making it easier for me to accept patches. d16225 3 a16227 3 you may write the new code, I have to maintain it and support it. If it isn't possible for me to do that with a minimum of extra work, then I probably will not. d16235 2 a16236 2 If you want to port `gawk' to a new operating system, there are several steps: d16238 2 a16239 2 1. Follow the guidelines in *Note Adding Code::, concerning coding style, submission of diffs, and so on. d16241 2 a16242 2 2. When doing a port, bear in mind that your code must coexist peacefully with the rest of `gawk' and the other ports. Avoid d16249 3 a16251 2 can, of course, distribute your changes on your own, as long as you comply with the GPL (*note Copying::). d16255 5 a16259 5 change them unless it is for a very good reason; i.e., changes are not out of the question, but changes to these files are scrutinized extra carefully. The files are `getopt.h', `getopt.c', `getopt1.c', `regex.h', `regex.c', `dfa.h', `dfa.c', `install-sh', and `mkinstalldirs'. d16263 3 a16265 3 to compile and run `gawk' on their systems. If noone volunteers to maintain a port, it becomes unsupported and it may be necessary to remove it from the distribution. d16275 1 a16275 1 machine or operating system for the port--for example, d16280 1 a16280 2 (Currently, this is only an issue for the PC operating system ports.) d16282 9 a16290 9 6. Supply a `Makefile' as well as any other C source and header files that are necessary for your operating system. All your code should be in a separate subdirectory, with a name that is the same as, or reminiscent of, either your operating system or the computer system. If possible, try to structure things so that it is not necessary to move files out of the subdirectory into the main source directory. If that is not possible, then be sure to avoid using names for your files that duplicate the names of files in the main source directory. d16294 1 a16294 1 steps needed to compile and/or install `gawk' for your system. d16298 4 a16301 541 the public domain and submit a signed statement to that effect, or assign the copyright in your code to the FSF. Both of these actions are easy to do and _many_ people have done so already. If you have questions, please contact me, or . Following these steps makes it much easier to integrate your changes into `gawk' and have them coexist happily with other operating systems' code that is already there. In the code that you supply and maintain, feel free to use a coding style and brace layout that suits your taste.  File: gawk.info, Node: Dynamic Extensions, Next: Future Extensions, Prev: Additions, Up: Notes Adding New Built-in Functions to `gawk' ======================================= Danger Will Robinson! Danger!! Warning! Warning! The Robot Beginning with `gawk' 3.1, it is possible to add new built-in functions to `gawk' using dynamically loaded libraries. This facility is available on systems (such as GNU/Linux) that support the `dlopen' and `dlsym' functions. This minor node describes how to write and use dynamically loaded extentions for `gawk'. Experience with programming in C or C++ is necessary when reading this minor node. *Caution:* The facilities described in this minor node are very much subject to change in the next `gawk' release. Be aware that you may have to re-do everything, perhaps from scratch, upon the next release. * Menu: * Internals:: A brief look at some `gawk' internals. * Sample Library:: A example of new functions.  File: gawk.info, Node: Internals, Next: Sample Library, Up: Dynamic Extensions A Minimal Introduction to `gawk' Internals ------------------------------------------ The truth is that `gawk' was not designed for simple extensibility. The facilities for adding functions using shared libraries work, but are something of a "bag on the side." Thus, this tour is brief and simplistic; would-be `gawk' hackers are encouraged to spend some time reading the source code before trying to write extensions based on the material presented here. Of particular note are the files `awk.h', `builtin.c', and `eval.c'. Reading `awk.y' in order to see how the parse tree is built would also be of use. With the disclaimers out of the way, the following types, structure members, functions, and macros are declared in `awk.h' and are of use when writing extensions. The next minor node shows how they are used: `AWKNUM' An `AWKNUM' is the internal type of `awk' floating-point numbers. Typically, it is a C `double'. `NODE' Just about everything is done using objects of type `NODE'. These contain both strings and numbers, as well as variables and arrays. `AWKNUM force_number(NODE *n)' This macro forces a value to be numeric. It returns the actual numeric value contained in the node. It may end up calling an internal `gawk' function. `void force_string(NODE *n)' This macro guarantees that a `NODE''s string value is current. It may end up calling an internal `gawk' function. It also guarantees that the string is zero-terminated. `n->param_cnt' The number of parameters actually passed in a function call at runtime. `n->stptr' `n->stlen' The data and length of a `NODE''s string value, respectively. The string is _not_ guaranteed to be zero-terminated. If you need to pass the string value to a C library function, save the value in `n->stptr[n->stlen]', assign `'\0'' to it, call the routine, and then restore the value. `n->type' The type of the `NODE'. This is a C `enum'. Values should be either `Node_var' or `Node_var_array' for function parameters. `n->vname' The "variable name" of a node. This is not of much use inside externally written extensions. `void assoc_clear(NODE *n)' Clears the associative array pointed to by `n'. Make sure that `n->type == Node_var_array' first. `NODE **assoc_lookup(NODE *symbol, NODE *subs, int reference)' Finds, and installs if necessary, array elements. `symbol' is the array, `subs' is the subscript. This is usually a value created with `tmp_string' (see below). `reference' should be `TRUE' if it is an error to use the value before it is created. Typically, `FALSE' is the correct value to use from extension functions. `NODE *make_string(char *s, size_t len)' Take a C string and turn it into a pointer to a `NODE' that can be stored appropriately. This is permanent storage; understanding of `gawk' memory management is helpful. `NODE *make_number(AWKNUM val)' Take an `AWKNUM' and turn it into a pointer to a `NODE' that can be stored appropriately. This is permanent storage; understanding of `gawk' memory management is helpful. `NODE *tmp_string(char *s, size_t len);' Take a C string and turn it into a pointer to a `NODE' that can be stored appropriately. This is temporary storage; understanding of `gawk' memory management is helpful. `NODE *tmp_number(AWKNUM val)' Take an `AWKNUM' and turn it into a pointer to a `NODE' that can be stored appropriately. This is temporary storage; understanding of `gawk' memory management is helpful. `NODE *dupnode(NODE *n)' Duplicate a node. In most cases, this increments an internal reference count instead of actually duplicating the entire `NODE'; understanding of `gawk' memory management is helpful. `void free_temp(NODE *n)' This macro releases the memory associated with a `NODE' allocated with `tmp_string' or `tmp_number'. Understanding of `gawk' memory management is helpful. `void make_builtin(char *name, NODE *(*func)(NODE *), int count)' Register a C function pointed to by `func' as new built-in function `name'. `name' is a regular C string. `count' is the maximum number of arguments that the function takes. The function should be written in the following manner: /* do_xxx --- do xxx function for gawk */ NODE * do_xxx(NODE *tree) { ... } `NODE *get_argument(NODE *tree, int i)' This function is called from within a C extension function to get the `i'-th argument from the function call. The first argument is argument zero. `void set_value(NODE *tree)' This function is called from within a C extension function to set the return value from the extension function. This value is what the `awk' program sees as the return value from the new `awk' function. `void update_ERRNO(void)' This function is called from within a C extension function to set the value of `gawk''s `ERRNO' variable, based on the current value of the C `errno' variable. It is provided as a convenience. An argument that is supposed to be an array needs to be handled with some extra code, in case the array being passed in is actually from a function parameter. In versions of `gawk' up to and including 3.1.2, the following boilerplate code shows how to do this: NODE *the_arg; the_arg = get_argument(tree, 2); /* assume need 3rd arg, 0-based */ /* if a parameter, get it off the stack */ if (the_arg->type == Node_param_list) the_arg = stack_ptr[the_arg->param_cnt]; /* parameter referenced an array, get it */ if (the_arg->type == Node_array_ref) the_arg = the_arg->orig_array; /* check type */ if (the_arg->type != Node_var && the_arg->type != Node_var_array) fatal("newfunc: third argument is not an array"); /* force it to be an array, if necessary, clear it */ the_arg->type = Node_var_array; assoc_clear(the_arg); For versions 3.1.3 and later, the internals changed. In particular, the interface was actually _simplified_ drastically. The following boilerplate code now suffices: NODE *the_arg; the_arg = get_argument(tree, 2); /* assume need 3rd arg, 0-based */ /* force it to be an array: */ the_arg = get_array(the_arg); /* if necessary, clear it: */ assoc_clear(the_arg); Again, you should spend time studying the `gawk' internals; don't just blindly copy this code.  File: gawk.info, Node: Sample Library, Prev: Internals, Up: Dynamic Extensions Directory and File Operation Built-ins -------------------------------------- Two useful functions that are not in `awk' are `chdir' (so that an `awk' program can change its directory) and `stat' (so that an `awk' program can gather information about a file). This minor node implements these functions for `gawk' in an external extension library. * Menu: * Internal File Description:: What the new functions will do. * Internal File Ops:: The code for internal file operations. * Using Internal File Ops:: How to use an external extension.  File: gawk.info, Node: Internal File Description, Next: Internal File Ops, Up: Sample Library Using `chdir' and `stat' ........................ This minor node shows how to use the new functions at the `awk' level once they've been integrated into the running `gawk' interpreter. Using `chdir' is very straightforward. It takes one argument, the new directory to change to: ... newdir = "/home/arnold/funstuff" ret = chdir(newdir) if (ret < 0) { printf("could not change to %s: %s\n", newdir, ERRNO) > "/dev/stderr" exit 1 } ... The return value is negative if the `chdir' failed, and `ERRNO' (*note Built-in Variables::) is set to a string indicating the error. Using `stat' is a bit more complicated. The C `stat' function fills in a structure that has a fair amount of information. The right way to model this in `awk' is to fill in an associative array with the appropriate information: file = "/home/arnold/.profile" fdata[1] = "x" # force `fdata' to be an array ret = stat(file, fdata) if (ret < 0) { printf("could not stat %s: %s\n", file, ERRNO) > "/dev/stderr" exit 1 } printf("size of %s is %d bytes\n", file, fdata["size"]) The `stat' function always clears the data array, even if the `stat' fails. It fills in the following elements: `"name"' The name of the file that was `stat''ed. `"dev"' `"ino"' The file's device and inode numbers, respectively. `"mode"' The file's mode, as a numeric value. This includes both the file's type and its permissions. `"nlink"' The number of hard links (directory entries) the file has. `"uid"' `"gid"' The numeric user and group ID numbers of the file's owner. `"size"' The size in bytes of the file. `"blocks"' The number of disk blocks the file actually occupies. This may not be a function of the file's size if the file has holes. `"atime"' `"mtime"' `"ctime"' The file's last access, modification, and inode update times, respectively. These are numeric timestamps, suitable for formatting with `strftime' (*note Built-in::). `"pmode"' The file's "printable mode." This is a string representation of the file's type and permissions, such as what is produced by `ls -l'--for example, `"drwxr-xr-x"'. `"type"' A printable string representation of the file's type. The value is one of the following: `"blockdev"' `"chardev"' The file is a block or character device ("special file"). `"directory"' The file is a directory. `"fifo"' The file is a named-pipe (also known as a FIFO). `"file"' The file is just a regular file. `"socket"' The file is an `AF_UNIX' ("Unix domain") socket in the filesystem. `"symlink"' The file is a symbolic link. Several additional elements may be present depending upon the operating system and the type of the file. You can test for them in your `awk' program by using the `in' operator (*note Reference to Elements::): `"blksize"' The preferred block size for I/O to the file. This field is not present on all POSIX-like systems in the C `stat' structure. `"linkval"' If the file is a symbolic link, this element is the name of the file the link points to (i.e., the value of the link). `"rdev"' `"major"' `"minor"' If the file is a block or character device file, then these values represent the numeric device number and the major and minor components of that number, respectively.  File: gawk.info, Node: Internal File Ops, Next: Using Internal File Ops, Prev: Internal File Description, Up: Sample Library C Code for `chdir' and `stat' ............................. Here is the C code for these extensions. They were written for GNU/Linux. The code needs some more work for complete portability to other POSIX-compliant systems:(1) #include "awk.h" #include /* do_chdir --- provide dynamically loaded chdir() builtin for gawk */ static NODE * do_chdir(tree) NODE *tree; { NODE *newdir; int ret = -1; newdir = get_argument(tree, 0); The file includes the `"awk.h"' header file for definitions for the `gawk' internals. It includes `' for access to the `major' and `minor' macros. By convention, for an `awk' function `foo', the function that implements it is called `do_foo'. The function should take a `NODE *' argument, usually called `tree', that represents the argument list to the function. The `newdir' variable represents the new directory to change to, retrieved with `get_argument'. Note that the first argument is numbered zero. This code actually accomplishes the `chdir'. It first forces the argument to be a string and passes the string value to the `chdir' system call. If the `chdir' fails, `ERRNO' is updated. The result of `force_string' has to be freed with `free_temp': if (newdir != NULL) { (void) force_string(newdir); ret = chdir(newdir->stptr); if (ret < 0) update_ERRNO(); free_temp(newdir); } Finally, the function returns the return value to the `awk' level, using `set_value'. Then it must return a value from the call to the new built-in (this value ignored by the interpreter): /* Set the return value */ set_value(tmp_number((AWKNUM) ret)); /* Just to make the interpreter happy */ return tmp_number((AWKNUM) 0); } The `stat' built-in is more involved. First comes a function that turns a numeric mode into a printable representation (e.g., 644 becomes `-rw-r--r--'). This is omitted here for brevity: /* format_mode --- turn a stat mode field into something readable */ static char * format_mode(fmode) unsigned long fmode; { ... } Next comes the actual `do_stat' function itself. First come the variable declarations and argument checking: /* do_stat --- provide a stat() function for gawk */ static NODE * do_stat(tree) NODE *tree; { NODE *file, *array; struct stat sbuf; int ret; char *msg; NODE **aptr; char *pmode; /* printable mode */ char *type = "unknown"; /* check arg count */ if (tree->param_cnt != 2) fatal( "stat: called with %d arguments, should be 2", tree->param_cnt); Then comes the actual work. First, we get the arguments. Then, we always clear the array. To get the file information, we use `lstat', in case the file is a symbolic link. If there's an error, we set `ERRNO' and return: /* * directory is first arg, * array to hold results is second */ file = get_argument(tree, 0); array = get_argument(tree, 1); /* empty out the array */ assoc_clear(array); /* lstat the file, if error, set ERRNO and return */ (void) force_string(file); ret = lstat(file->stptr, & sbuf); if (ret < 0) { update_ERRNO(); set_value(tmp_number((AWKNUM) ret)); free_temp(file); return tmp_number((AWKNUM) 0); } Now comes the tedious part: filling in the array. Only a few of the calls are shown here, since they all follow the same pattern: /* fill in the array */ aptr = assoc_lookup(array, tmp_string("name", 4), FALSE); *aptr = dupnode(file); aptr = assoc_lookup(array, tmp_string("mode", 4), FALSE); *aptr = make_number((AWKNUM) sbuf.st_mode); aptr = assoc_lookup(array, tmp_string("pmode", 5), FALSE); pmode = format_mode(sbuf.st_mode); *aptr = make_string(pmode, strlen(pmode)); When done, we free the temporary value containing the file name, set the return value, and return: free_temp(file); /* Set the return value */ set_value(tmp_number((AWKNUM) ret)); /* Just to make the interpreter happy */ return tmp_number((AWKNUM) 0); } Finally, it's necessary to provide the "glue" that loads the new function(s) into `gawk'. By convention, each library has a routine named `dlload' that does the job: /* dlload --- load new builtins in this library */ NODE * dlload(tree, dl) NODE *tree; void *dl; { make_builtin("chdir", do_chdir, 1); make_builtin("stat", do_stat, 2); return tmp_number((AWKNUM) 0); } And that's it! As an exercise, consider adding functions to implement system calls such as `chown', `chmod', and `umask'. ---------- Footnotes ---------- (1) This version is edited slightly for presentation. The complete version can be found in `extension/filefuncs.c' in the `gawk' distribution.  File: gawk.info, Node: Using Internal File Ops, Prev: Internal File Ops, Up: Sample Library Integrating the Extensions .......................... Now that the code is written, it must be possible to add it at runtime to the running `gawk' interpreter. First, the code must be compiled. Assuming that the functions are in a file named `filefuncs.c', and IDIR is the location of the `gawk' include files, the following steps create a GNU/Linux shared library: $ gcc -shared -DHAVE_CONFIG_H -c -O -g -IIDIR filefuncs.c $ ld -o filefuncs.so -shared filefuncs.o d16303 3 a16305 6 Once the library exists, it is loaded by calling the `extension' built-in function. This function takes two arguments: the name of the library to load and the name of a function to call when the library is first loaded. This function adds the new functions to `gawk'. It returns the value returned by the initialization function within the shared library: d16307 2 a16308 37 # file testff.awk BEGIN { extension("./filefuncs.so", "dlload") chdir(".") # no-op data[1] = 1 # force `data' to be an array print "Info for testff.awk" ret = stat("testff.awk", data) print "ret =", ret for (i in data) printf "data[\"%s\"] = %s\n", i, data[i] print "testff.awk modified:", strftime("%m %d %y %H:%M:%S", data["mtime"]) } Here are the results of running the program: $ gawk -f testff.awk -| Info for testff.awk -| ret = 0 -| data["blksize"] = 4096 -| data["mtime"] = 932361936 -| data["mode"] = 33188 -| data["type"] = file -| data["dev"] = 2065 -| data["gid"] = 10 -| data["ino"] = 878597 -| data["ctime"] = 971431797 -| data["blocks"] = 2 -| data["nlink"] = 1 -| data["name"] = testff.awk -| data["atime"] = 971608519 -| data["pmode"] = -rw-r--r-- -| data["size"] = 607 -| data["uid"] = 2076 -| testff.awk modified: 07 19 99 08:25:36 d16311 1 a16311 1 File: gawk.info, Node: Future Extensions, Prev: Dynamic Extensions, Up: Notes d16318 1 a16318 1 d16322 3 a16324 3 This minor node briefly lists extensions and possible improvements that indicate the directions we are currently considering for `gawk'. The file `FUTURES' in the `gawk' distribution lists these extensions as d16327 2 a16328 2 Following is a list of probable future changes visible at the `awk' language level: d16330 6 a16335 17 Loadable module interface It is not clear that the `awk'-level interface to the modules facility is as good as it should be. The interface needs to be redesigned, particularly taking namespace issues into account, as well as possibly including issues such as library search path order and versioning. `RECLEN' variable for fixed-length records Along with `FIELDWIDTHS', this would speed up the processing of fixed-length records. `PROCINFO["RS"]' would be `"RS"' or `"RECLEN"', depending upon which kind of record processing is in effect. Additional `printf' specifiers The 1999 ISO C standard added a number of additional `printf' format specifiers. These should be evaluated for possible inclusion in `gawk'. d16341 5 a16345 3 Large character sets It would be nice if `gawk' could handle UTF-8 and other character sets that are larger than eight bits. d16350 11 a16360 2 Following is a list of probable improvements that will make `gawk''s source code easier to work with: d16362 31 a16392 32 Loadable module mechanics The current extension mechanism works (*note Dynamic Extensions::), but is rather primitive. It requires a fair amount of manual work to create and integrate a loadable module. Nor is the current mechanism as portable as might be desired. The GNU `libtool' package provides a number of features that would make using loadable modules much easier. `gawk' should be changed to use `libtool'. Loadable module internals The API to its internals that `gawk' "exports" should be revised. Too many things are needlessly exposed. A new API should be designed and implemented to make module writing easier. Better array subscript management `gawk''s management of array subscript storage could use revamping, so that using the same value to index multiple arrays only stores one copy of the index value. Integrating the DBUG library Integrating Fred Fish's DBUG library would be helpful during development, but it's a lot of work to do. Following is a list of probable improvements that will make `gawk' perform better: Compilation of `awk' programs `gawk' uses a Bison (YACC-like) parser to convert the script given it into a syntax tree; the syntax tree is then executed by a simple recursive evaluator. This method incurs a lot of overhead, since the recursive evaluator performs many procedure calls to do even the simplest things. d16400 1 a16400 1 An easier possibility might be for an intermediate phase of `gawk' d16407 2 a16408 309 Finally, the programs in the test suite could use documenting in this Info file. *Note Additions::, if you are interested in tackling any of these projects.  File: gawk.info, Node: Basic Concepts, Next: Glossary, Prev: Notes, Up: Top Basic Programming Concepts ************************** This major node attempts to define some of the basic concepts and terms that are used throughout the rest of this Info file. As this Info file is specifically about `awk', and not about computer programming in general, the coverage here is by necessity fairly cursory and simplistic. (If you need more background, there are many other introductory texts that you should refer to instead.) * Menu: * Basic High Level:: The high level view. * Basic Data Typing:: A very quick intro to data types. * Floating Point Issues:: Stuff to know about floating-point numbers.  File: gawk.info, Node: Basic High Level, Next: Basic Data Typing, Up: Basic Concepts What a Program Does =================== At the most basic level, the job of a program is to process some input data and produce results. _______ +------+ / \ +---------+ | Data | -----> < Program > -----> | Results | +------+ \_______/ +---------+ The "program" in the figure can be either a compiled program(1) (such as `ls'), or it may be "interpreted". In the latter case, a machine-executable program such as `awk' reads your program, and then uses the instructions in your program to process the data. When you write a program, it usually consists of the following, very basic set of steps: ______ +----------------+ / More \ No +----------+ | Initialization | -------> < Data > -------> | Clean Up | +----------------+ ^ \ ? / +----------+ | +--+-+ | | Yes | | | V | +---------+ +-----+ Process | +---------+ Initialization These are the things you do before actually starting to process data, such as checking arguments, initializing any data you need to work with, and so on. This step corresponds to `awk''s `BEGIN' rule (*note BEGIN/END::). If you were baking a cake, this might consist of laying out all the mixing bowls and the baking pan, and making sure you have all the ingredients that you need. Processing This is where the actual work is done. Your program reads data, one logical chunk at a time, and processes it as appropriate. In most programming languages, you have to manually manage the reading of data, checking to see if there is more each time you read a chunk. `awk''s pattern-action paradigm (*note Getting Started::) handles the mechanics of this for you. In baking a cake, the processing corresponds to the actual labor: breaking eggs, mixing the flour, water, and other ingredients, and then putting the cake into the oven. Clean Up Once you've processed all the data, you may have things you need to do before exiting. This step corresponds to `awk''s `END' rule (*note BEGIN/END::). After the cake comes out of the oven, you still have to wrap it in plastic wrap to keep anyone from tasting it, as well as wash the mixing bowls and utensils. An "algorithm" is a detailed set of instructions necessary to accomplish a task, or process data. It is much the same as a recipe for baking a cake. Programs implement algorithms. Often, it is up to you to design the algorithm and implement it, simultaneously. The "logical chunks" we talked about previously are called "records", similar to the records a company keeps on employees, a school keeps for students, or a doctor keeps for patients. Each record has many component parts, such as first and last names, date of birth, address, and so on. The component parts are referred to as the "fields" of the record. The act of reading data is termed "input", and that of generating results, not too surprisingly, is termed "output". They are often referred to together as "input/output," and even more often, as "I/O" for short. (You will also see "input" and "output" used as verbs.) `awk' manages the reading of data for you, as well as the breaking it up into records and fields. Your program's job is to tell `awk' what to with the data. You do this by describing "patterns" in the data to look for, and "actions" to execute when those patterns are seen. This "data-driven" nature of `awk' programs usually makes them both easier to write and easier to read. ---------- Footnotes ---------- (1) Compiled programs are typically written in lower-level languages such as C, C++, Fortran, or Ada, and then translated, or "compiled", into a form that the computer can execute directly.  File: gawk.info, Node: Basic Data Typing, Next: Floating Point Issues, Prev: Basic High Level, Up: Basic Concepts Data Values in a Computer ========================= In a program, you keep track of information and values in things called "variables". A variable is just a name for a given value, such as `first_name', `last_name', `address', and so on. `awk' has several predefined variables, and it has special names to refer to the current input record and the fields of the record. You may also group multiple associated values under one name, as an array. Data, particularly in `awk', consists of either numeric values, such as 42 or 3.1415927, or string values. String values are essentially anything that's not a number, such as a name. Strings are sometimes referred to as "character data", since they store the individual characters that comprise them. Individual variables, as well as numeric and string variables, are referred to as "scalar" values. Groups of values, such as arrays, are not scalars. Within computers, there are two kinds of numeric values: "integers" and "floating-point". In school, integer values were referred to as "whole" numbers--that is, numbers without any fractional part, such as 1, 42, or -17. The advantage to integer numbers is that they represent values exactly. The disadvantage is that their range is limited. On most modern systems, this range is -2,147,483,648 to 2,147,483,647. Integer values come in two flavors: "signed" and "unsigned". Signed values may be negative or positive, with the range of values just described. Unsigned values are always positive. On most modern systems, the range is from 0 to 4,294,967,295. Floating-point numbers represent what are called "real" numbers; i.e., those that do have a fractional part, such as 3.1415927. The advantage to floating-point numbers is that they can represent a much larger range of values. The disadvantage is that there are numbers that they cannot represent exactly. `awk' uses "double-precision" floating-point numbers, which can hold more digits than "single-precision" floating-point numbers. Floating-point issues are discussed more fully in *Note Floating Point Issues::. At the very lowest level, computers store values as groups of binary digits, or "bits". Modern computers group bits into groups of eight, called "bytes". Advanced applications sometimes have to manipulate bits directly, and `gawk' provides functions for doing so. While you are probably used to the idea of a number without a value (i.e., zero), it takes a bit more getting used to the idea of zero-length character data. Nevertheless, such a thing exists. It is called the "null string". The null string is character data that has no value. In other words, it is empty. It is written in `awk' programs like this: `""'. Humans are used to working in decimal; i.e., base 10. In base 10, numbers go from 0 to 9, and then "roll over" into the next column. (Remember grade school? 42 is 4 times 10 plus 2.) There are other number bases though. Computers commonly use base 2 or "binary", base 8 or "octal", and base 16 or "hexadecimal". In binary, each column represents two times the value in the column to its right. Each column may contain either a 0 or a 1. Thus, binary 1010 represents 1 times 8, plus 0 times 4, plus 1 times 2, plus 0 times 1, or decimal 10. Octal and hexadecimal are discussed more in *Note Nondecimal-numbers::. Programs are written in programming languages. Hundreds, if not thousands, of programming languages exist. One of the most popular is the C programming language. The C language had a very strong influence on the design of the `awk' language. There have been several versions of C. The first is often referred to as "K&R" C, after the initials of Brian Kernighan and Dennis Ritchie, the authors of the first book on C. (Dennis Ritchie created the language, and Brian Kernighan was one of the creators of `awk'.) In the mid-1980s, an effort began to produce an international standard for C. This work culminated in 1989, with the production of the ANSI standard for C. This standard became an ISO standard in 1990. Where it makes sense, POSIX `awk' is compatible with 1990 ISO C. In 1999, a revised ISO C standard was approved and released. Future versions of `gawk' will be as compatible as possible with this standard.  File: gawk.info, Node: Floating Point Issues, Prev: Basic Data Typing, Up: Basic Concepts Floating-Point Number Caveats ============================= As mentioned earlier, floating-point numbers represent what are called "real" numbers, i.e., those that have a fractional part. `awk' uses double-precision floating-point numbers to represent all numeric values. This minor node describes some of the issues involved in using floating-point numbers. There is a very nice paper on floating-point arithmetic by David Goldberg, "What Every Computer Scientist Should Know About Floating-point Arithmetic," `ACM Computing Surveys' *23*, 1 (1991-03), 5-48.(1) This is worth reading if you are interested in the details, but it does require a background in computer science. Internally, `awk' keeps both the numeric value (double-precision floating-point) and the string value for a variable. Separately, `awk' keeps track of what type the variable has (*note Typing and Comparison::), which plays a role in how variables are used in comparisons. It is important to note that the string value for a number may not reflect the full value (all the digits) that the numeric value actually contains. The following program (`values.awk') illustrates this: { $1 = $2 + $3 # see it for what it is printf("$1 = %.12g\n", $1) # use CONVFMT a = "<" $1 ">" print "a =", a # use OFMT print "$1 =", $1 } This program shows the full value of the sum of `$2' and `$3' using `printf', and then prints the string values obtained from both automatic conversion (via `CONVFMT') and from printing (via `OFMT'). Here is what happens when the program is run: $ echo 2 3.654321 1.2345678 | awk -f values.awk -| $1 = 4.8888888 -| a = <4.88889> -| $1 = 4.88889 This makes it clear that the full numeric value is different from what the default string representations show. `CONVFMT''s default value is `"%.6g"', which yields a value with at least six significant digits. For some applications, you might want to change it to specify more precision. On most modern machines, most of the time, 17 digits is enough to capture a floating-point number's value exactly.(2) Unlike numbers in the abstract sense (such as what you studied in high school or college math), numbers stored in computers are limited in certain ways. They cannot represent an infinite number of digits, nor can they always represent things exactly. In particular, floating-point numbers cannot always represent values exactly. Here is an example: $ awk '{ printf("%010d\n", $1 * 100) }' 515.79 -| 0000051579 515.80 -| 0000051579 515.81 -| 0000051580 515.82 -| 0000051582 Ctrl-d This shows that some values can be represented exactly, whereas others are only approximated. This is not a "bug" in `awk', but simply an artifact of how computers represent numbers. Another peculiarity of floating-point numbers on modern systems is that they often have more than one representation for the number zero! In particular, it is possible to represent "minus zero" as well as regular, or "positive" zero. This example shows that negative and positive zero are distinct values when stored internally, but that they are in fact equal to each other, as well as to "regular" zero: $ gawk 'BEGIN { mz = -0 ; pz = 0 > printf "-0 = %g, +0 = %g, (-0 == +0) -> %d\n", mz, pz, mz == pz > printf "mz == 0 -> %d, pz == 0 -> %d\n", mz == 0, pz == 0 > }' -| -0 = -0, +0 = 0, (-0 == +0) -> 1 -| mz == 0 -> 1, pz == 0 -> 1 It helps to keep this in mind should you process numeric data that contains negative zero values; the fact that the zero is negative is noted and can affect comparisons. ---------- Footnotes ---------- (1) `http://www.validlab.com/goldberg/paper.ps'. d16410 2 a16411 2 (2) Pathological cases can require up to 752 digits (!), but we doubt that you need to worry about this. d16414 1 a16414 1 File: gawk.info, Node: Glossary, Next: Copying, Prev: Basic Concepts, Up: Top d16422 2 a16423 2 Actions are always enclosed in curly braces. (*Note Action Overview::.) d16427 2 a16428 2 assembler completely as `sed' and `awk' scripts. It is thousands of lines long, including machine descriptions for several eight-bit d16430 1 a16430 2 been better written in another language. You can get it from `ftp://ftp.freefriends.org/arnold/Awkstuff/aaa.tgz'. d16435 1 a16435 7 formatting commands, using `awk' and `sh'. It is available over the Internet from `ftp://ftp.freefriends.org/arnold/Awkstuff/awf.tgz'. Anchor The regexp metacharacters `^' and `$', which force the match to the beginning or end of the string, respectively. d16440 1 a16440 11 C++ programming languages. These standards often become international standards as well. See also "ISO." Array A grouping of multiple values under the same name. Most languages just provide sequential arrays. `awk' provides associative arrays. Assertion A statement in a program that a condition is true at this point in the program. Useful for reasoning about how a program is supposed to behave. d16446 1 a16446 5 Assignment Ops::. Associative Array Arrays in which the indices may be numbers or strings, not just sequential integers in a fixed range. d16461 2 a16462 2 The GNU version of the standard shell (the Bourne-Again SHell). See also "Bourne Shell." a16466 14 Bit Short for "Binary Digit." All values in computer memory ultimately reduce to binary digits: values that are either zero or one. Groups of bits may be interpreted differently--as integers, floating-point numbers, character data, addresses of other memory objects, or other data. `awk' lets you work with floating-point numbers and strings. `gawk' lets you manipulate bit values with the built-in functions described in *Note Bitwise Functions::. Computers are often defined by how many bits they use to represent integer values. Typical systems are 32-bit systems, but 64-bit systems are becoming increasingly popular, and 16-bit systems are waning in popularity. d16468 1 a16468 1 Named after the English mathematician Boole. See also "Logical d16473 3 a16475 3 originally written by Steven R. Bourne. Many shells (`bash', `ksh', `pdksh', `zsh') are generally upwardly compatible with the Bourne shell. d16479 3 a16481 5 numerical, I/O-related, and string computations. Examples are `sqrt' (for the square root of a number) and `substr' (for a substring of a string). `gawk' provides functions for timestamp management, bit manipulation, and runtime string translation. (*Note Built-in::.) d16484 7 a16490 8 `ARGC', `ARGV', `CONVFMT', `ENVIRON', `FILENAME', `FNR', `FS', `NF', `NR', `OFMT', `OFS', `ORS', `RLENGTH', `RSTART', `RS', and `SUBSEP' are the variables that have special meaning to `awk'. In addition, `ARGIND', `BINMODE', `ERRNO', `FIELDWIDTHS', `IGNORECASE', `LINT', `PROCINFO', `RT', and `TEXTDOMAIN' are the variables that have special meaning to `gawk'. Changing some of them affects `awk''s running environment. (*Note Built-in Variables::.) a16505 7 In general, `gawk' attempts to be as similar to the 1990 version of ISO C as makes sense. Future versions of `gawk' may adopt features from the newer 1999 standard, as appropriate. C++ A popular object-oriented programming language derived from C. d16518 1 a16518 10 `http://cm.bell-labs.com/netlib/typesetting/chem.gz'. Coprocess A subordinate program with which two-way communications is possible. Compiler A program that translates human-readable source code into machine-executable object code. The object code is then executed directly by the computer. See also "Interpreter." d16522 2 a16523 1 statements may be nested. (*Note Statements::.) d16527 1 a16527 1 another, producing a new string. For example, the string `foo' d16529 1 a16529 1 (*Note Concatenation::.) d16534 1 a16534 1 is true, the value of the whole expression is the value of EXPR2; d16536 2 a16537 1 and EXPR3 is evaluated. (*Note Conditional Exp::.) d16543 2 a16544 1 process. (*Note Typing and Comparison::.) d16553 1 a16553 1 Such areas are marked in this Info file with "(d.c.)" in the text a16555 5 Data Driven A description of `awk' programs, where you specify the data you are interested in processing, and what to do when that data is seen. d16558 2 a16559 6 converted into strings and vice versa, as needed. (*Note Conversion::.) Deadlock The situation in which two communicating processes are each waiting for the other to perform an action. d16561 1 a16561 1 Double-Precision d16563 4 a16566 4 parts. Double-precision numbers keep track of more digits than do single-precision numbers, but operations on them are sometimes more expensive. This is the way `awk' stores numeric values. It is the C type `double'. d16572 1 a16572 1 (*Note Computed Regexps::.) a16582 9 Epoch The date used as the "beginning of time" for timestamps. Time values in Unix systems are represented as seconds since the epoch, with library functions available for converting these values into standard date and time formats. The epoch on Unix and POSIX systems is 1970-01-01 00:00:00 UTC. See also "GMT" and "UTC." d16584 3 a16586 6 A special sequence of characters used for describing nonprinting characters, such as `\n' for newline or `\033' for the ASCII ESC (Escape) character. (*Note Escape Sequences::.) FDL See "Free Documentation License." d16590 1 a16590 1 separated by whitespace (or by a separator regexp that you can d16593 8 a16600 11 built-in variable `FIELDWIDTHS' to describe their lengths. (*Note Field Separators::, and *Note Constant Size::.) Flag A variable whose truth value indicates the existence or nonexistence of some condition. Floating-Point Number Often referred to in mathematical terms as a "rational" or real number, this is just a number that can have a fractional part. See also "Double-Precision" and "Single-Precision." d16604 1 a16604 2 `strftime' and `sprintf' functions, and are used in the `printf' statement as well. Also, data conversions from numbers to strings d16606 1 a16606 6 variable `CONVFMT'. (*Note Control Letters::.) Free Documentation License This document describes the terms under which this Info file is published and may be copied. (*Note GNU Free Documentation License::.) d16611 2 a16612 1 and also allows you to define your own. (*Note Functions::.) d16618 1 a16618 1 A nonprofit organization dedicated to the production and d16628 2 a16629 6 code may be distributed. (*Note Copying::.) GMT "Greenwich Mean Time." This is the old term for UTC. It is the time of day used as the epoch for Unix and POSIX systems. See also "Epoch" and "UTC." a16635 9 GNU/Linux A variant of the GNU system using the Linux kernel, instead of the Free Software Foundation's Hurd kernel. Linux is a stable, efficient, full-featured clone of Unix that has been ported to a variety of architectures. It is most popular on PC-class systems, but runs well on a variety of other systems too. The Linux kernel source code is available under the terms of the GNU General Public License, which is perhaps its most important aspect. d16641 1 a16641 1 `A' representing 10, `B' representing 11, and so on, up to `F' for d16643 1 a16643 1 indicate their base. Thus, `0x12' is 18 (1 times 16 plus 2). d16650 3 a16652 3 A single chunk of data that is read in by `awk'. Usually, an `awk' input record consists of one line of text. (*Note Records::.) d16655 1 a16655 25 A whole number, i.e., a number that does not have a fractional part. Internationalization The process of writing or modifying a program so that it can use multiple languages without requiring further source code changes. Interpreter A program that reads human-readable source code directly, and uses the instructions in it to process data and produce results. `awk' is typically (but not always) implemented as an interpreter. See also "Compiler." Interval Expression A component of a regular expression that lets you specify repeated matches of some part of the regexp. Interval expressions were not traditionally available in `awk' programs. ISO The International Standards Organization. This organization produces international standards for many things, including programming languages, such as C and C++. In the computer arena, important standards like those for C, C++, and POSIX become both American national and ISO international standards simultaneously. This Info file refers to Standard C as "ISO C" throughout. a16665 15 Lesser General Public License This document describes the terms under which binary library archives or shared objects, and their source code may be distributed. Linux See "GNU/Linux." LGPL See "Lesser General Public License." Localization The process of providing the data necessary for an internationalized program to work in a particular language. a16677 10 Matching The act of testing a string against a regular expression. If the regexp describes the contents of the string, it is said to "match" it. Metacharacters Characters used within a regexp that do not stand for themselves. Instead, they denote regular expression operations, such as repetition, grouping, or alternation. d16680 1 a16680 1 `awk' programs by placing two double quote characters next to each d16685 3 a16687 3 A numeric-valued data object. Modern `awk' implementations use double-precision floating-point to represent numbers. Very old `awk' implementations use single-precision floating-point. a16693 3 P1003.2 See "POSIX." d16701 2 a16702 2 the input record against a regular expression. (*Note Pattern Overview::.) d16705 7 a16711 11 The name for a series of standards that specify a Portable Operating System interface. The "IX" denotes the Unix heritage of these standards. The main standard of interest for `awk' users is `IEEE Standard for Information Technology, Standard 1003.2-1992, Portable Operating System Interface (POSIX) Part 2: Shell and Utilities'. Informally, this standard is often referred to as simply "P1003.2." Precedence The order in which operations are performed when operators are used without explicit parentheses. d16715 3 a16717 3 library functions and not for the main `awk' program. Special care must be taken when naming such variables and functions. (*Note Library Names::.) d16720 3 a16722 3 A sequence of consecutive lines from the input file(s). A pattern can specify ranges of input lines for `awk' to process or it can specify single lines. (*Note Pattern Overview::.) d16729 2 a16730 3 Redirection means performing input from something other than the standard input stream, or performing output to something other than the standard output stream. d16733 1 a16733 1 to a file or a system command, using the `>', `>>', `|', and `|&' d16735 3 a16737 2 the `<', `|', and `|&' operators. (*Note Redirection::, and *Note Getline::.) d16745 1 a16745 1 escape sequences. (*Note Regexp::.) d16753 2 a16754 2 when you write the `awk' program and cannot be changed during its execution. (*Note Regexp Usage::.) a16767 13 Scalar A single value, be it a number or a string. Regular variables are scalars; arrays and functions are not. Search Path In `gawk', a list of directories to search for `awk' program source files. In the shell, a list of directories to search for executable programs. Seed The initial value, or starting point, for a sequence of random numbers. a16770 5 Shell The command interpreter for Unix and POSIX-compliant systems. The shell works both interactively, and as a programming language for batch files, or shell scripts. d16773 3 a16775 3 value of the entire expression is determinable from evaluating just the lefthand side of these operators, the righthand side is not evaluated. (*Note Boolean Ops::.) d16780 2 a16781 2 decrement expressions, and function calls have side effects. (*Note Assignment Ops::.) d16783 1 a16783 1 Single-Precision d16785 5 a16789 5 parts. Single-precision numbers keep track of fewer digits than do double-precision numbers, but operations on them are sometimes less expensive in terms of CPU time. This is the type used by some very old versions of `awk' to store numeric values. It is the C type `float'. d16796 2 a16797 2 handed directly to the underlying operating system--for example, `/dev/stderr'. (*Note Special Files::.) d16803 2 a16804 2 before starting to do anything, as well as with interactive programs which require input from the user. d16808 3 a16810 3 string'. Constant strings are written with double quotes in the `awk' language and may contain escape sequences. (*Note Escape Sequences::.) a16815 9 Text Domain A unique name that identifies an application. Used for grouping messages that are translated at runtime into the local language. Timestamp A value in the "seconds since the epoch" format used by Unix and POSIX systems. Used for the `gawk' functions `mktime', `strftime', and `systime'. See also "Epoch" and "UTC." d16819 2 a16820 2 universities around the world and later moved into commercial environments as a software development system and network server d16823 1 a16823 7 (such as GNU/Linux, NetBSD, FreeBSD, and OpenBSD). UTC The accepted abbreviation for "Universal Coordinated Time." This is standard time in Greenwich, England, which is used as a reference time for day and date calculations. See also "Epoch" and "GMT." d16826 1 a16826 1 A sequence of space, TAB, or newline characters occurring inside d16830 1 a16830 1 File: gawk.info, Node: Copying, Next: GNU Free Documentation License, Prev: Glossary, Up: Top d16832 1 a16832 1 GNU General Public License d16836 1 d16838 1 a16838 1 59 Temple Place, Suite 330, Boston, MA 02111, USA d16895 1 d16991 1 a16991 1 allowed only for noncommercial distribution and only if you d17141 1 a17141 1 Copyright (C) YEAR NAME OF AUTHOR d17155 1 a17155 1 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. d17163 1 a17163 1 Gnomovision version 69, Copyright (C) YEAR NAME OF AUTHOR d17191 1 a17191 432 GNU Lesser General Public License instead of this License.  File: gawk.info, Node: GNU Free Documentation License, Next: Index, Prev: Copying, Up: Top GNU Free Documentation License ****************************** Version 1.2, November 2002 Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. PREAMBLE The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others. 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If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software. d17194 1 a17194 1 File: gawk.info, Node: Index, Prev: GNU Free Documentation License, Up: Top d17201 11 a17211 64 * ! (exclamation point), ! operator: Boolean Ops. * ! (exclamation point), ! operator <1>: Egrep Program. * ! (exclamation point), ! operator: Precedence. * ! (exclamation point), != operator <1>: Precedence. * ! (exclamation point), != operator: Typing and Comparison. * ! (exclamation point), !~ operator <1>: Expression Patterns. * ! (exclamation point), !~ operator <2>: Precedence. * ! (exclamation point), !~ operator <3>: Typing and Comparison. * ! (exclamation point), !~ operator <4>: Regexp Constants. * ! (exclamation point), !~ operator <5>: Computed Regexps. * ! (exclamation point), !~ operator <6>: Case-sensitivity. * ! (exclamation point), !~ operator: Regexp Usage. * ! operator <1>: Egrep Program. * ! operator: Ranges. * " (double quote) <1>: Quoting. * " (double quote): Read Terminal. * " (double quote), regexp constants: Computed Regexps. * # (number sign), #! (executable scripts): Executable Scripts. * # (number sign), #! (executable scripts), portability issues with: Executable Scripts. * # (number sign), commenting: Comments. * $ (dollar sign): Regexp Operators. * $ (dollar sign), $ field operator <1>: Precedence. * $ (dollar sign), $ field operator: Fields. * $ (dollar sign), incrementing fields and arrays: Increment Ops. * $ field operator: Fields. * % (percent sign), % operator: Precedence. * % (percent sign), %= operator <1>: Precedence. * % (percent sign), %= operator: Assignment Ops. * & (ampersand), && operator <1>: Precedence. * & (ampersand), && operator: Boolean Ops. * & (ampersand), gsub/gensub/sub functions and: Gory Details. * ' (single quote) <1>: Quoting. * ' (single quote) <2>: Long. * ' (single quote): One-shot. * ' (single quote), vs. apostrophe: Comments. * ' (single quote), with double quotes: Quoting. * () (parentheses): Regexp Operators. * () (parentheses), pgawk program: Profiling. * * (asterisk), * operator, as multiplication operator: Precedence. * * (asterisk), * operator, as regexp operator: Regexp Operators. * * (asterisk), * operator, null strings, matching: Gory Details. * * (asterisk), ** operator <1>: Options. * * (asterisk), ** operator <2>: Precedence. * * (asterisk), ** operator: Arithmetic Ops. * * (asterisk), **= operator <1>: Options. * * (asterisk), **= operator <2>: Precedence. * * (asterisk), **= operator: Assignment Ops. * * (asterisk), *= operator <1>: Precedence. * * (asterisk), *= operator: Assignment Ops. * + (plus sign): Regexp Operators. * + (plus sign), + operator: Precedence. * + (plus sign), ++ operator <1>: Precedence. * + (plus sign), ++ operator: Increment Ops. * + (plus sign), += operator <1>: Precedence. * + (plus sign), += operator: Assignment Ops. * + (plus sign), decrement/increment operators: Increment Ops. * , (comma), in range patterns: Ranges. * - (hyphen), - operator: Precedence. * - (hyphen), -- (decrement/increment) operator: Precedence. * - (hyphen), -- operator: Increment Ops. * - (hyphen), -= operator <1>: Precedence. * - (hyphen), -= operator: Assignment Ops. * - (hyphen), filenames beginning with: Options. * - (hyphen), in character lists: Character Lists. a17215 7 * --disable-lint configuration option: Additional Configuration Options. * --disable-nls configuration option: Additional Configuration Options. * --dump-variables option <1>: Library Names. * --dump-variables option: Options. * --enable-portals configuration option <1>: Additional Configuration Options. * --enable-portals configuration option: Portal Files. * --enable-switch configuration option: Additional Configuration Options. a17217 2 * --gen-po option <1>: Options. * --gen-po option: String Extraction. d17219 1 a17219 2 * --lint option <1>: Options. * --lint option: Command Line. a17220 3 * --non-decimal-data option <1>: Options. * --non-decimal-data option: Nondecimal Data. * --non-decimal-data option, strtonum function and: Nondecimal Data. a17221 4 * --posix option, --traditional option and: Options. * --profile option <1>: Options. * --profile option: Profiling. * --re-interval option: Options. a17223 1 * --traditional option, --posix option and: Options. d17226 3 a17228 3 * --with-included-gettext configuration option <1>: Additional Configuration Options. * --with-included-gettext configuration option: Gawk I18N. * --with-included-gettext configuration option, configuring gawk with: Additional Configuration Options. a17229 7 * -F option <1>: Options. * -F option: Command Line Field Separator. * -f option: Long. * -F option, -Ft sets FS to TAB: Options. * -f option, on command line: Options. * -F option, troubleshooting: Known Bugs. * -mf/-mr options: Options. a17230 1 * -v option, variables, assigning: Assignment Options. d17232 26 a17257 88 * . (period): Regexp Operators. * .mo files: Explaining gettext. * .mo files, converting from .po: I18N Example. * .mo files, specifying directory of <1>: Programmer i18n. * .mo files, specifying directory of: Explaining gettext. * .po files <1>: Translator i18n. * .po files: Explaining gettext. * .po files, converting to .mo: I18N Example. * / (forward slash): Regexp. * / (forward slash), / operator: Precedence. * / (forward slash), /= operator <1>: Precedence. * / (forward slash), /= operator: Assignment Ops. * / (forward slash), /= operator, vs. /=.../ regexp constant: Assignment Ops. * / (forward slash), patterns and: Expression Patterns. * /= operator vs. /=.../ regexp constant: Assignment Ops. * /dev/... special files (gawk): Special FD. * /inet/ files (gawk): TCP/IP Networking. * /p files (gawk): Portal Files. * ; (semicolon): Statements/Lines. * ; (semicolon), AWKPATH variable and: PC Using. * ; (semicolon), separating statements in actions <1>: Statements. * ; (semicolon), separating statements in actions: Action Overview. * < (left angle bracket), < operator <1>: Precedence. * < (left angle bracket), < operator: Typing and Comparison. * < (left angle bracket), < operator (I/O): Getline/File. * < (left angle bracket), <= operator <1>: Precedence. * < (left angle bracket), <= operator: Typing and Comparison. * = (equals sign), = operator: Assignment Ops. * = (equals sign), == operator <1>: Precedence. * = (equals sign), == operator: Typing and Comparison. * > (right angle bracket), > operator <1>: Precedence. * > (right angle bracket), > operator: Typing and Comparison. * > (right angle bracket), > operator (I/O): Redirection. * > (right angle bracket), >= operator <1>: Precedence. * > (right angle bracket), >= operator: Typing and Comparison. * > (right angle bracket), >> operator (I/O) <1>: Precedence. * > (right angle bracket), >> operator (I/O): Redirection. * ? (question mark) <1>: GNU Regexp Operators. * ? (question mark): Regexp Operators. * ? (question mark), ?: operator: Precedence. * [] (square brackets): Regexp Operators. * \ (backslash) <1>: Regexp Operators. * \ (backslash) <2>: Quoting. * \ (backslash) <3>: Comments. * \ (backslash): Read Terminal. * \ (backslash), \" escape sequence: Escape Sequences. * \ (backslash), \' operator (gawk): GNU Regexp Operators. * \ (backslash), \/ escape sequence: Escape Sequences. * \ (backslash), \< operator (gawk): GNU Regexp Operators. * \ (backslash), \> operator (gawk): GNU Regexp Operators. * \ (backslash), \` operator (gawk): GNU Regexp Operators. * \ (backslash), \a escape sequence: Escape Sequences. * \ (backslash), \b escape sequence: Escape Sequences. * \ (backslash), \B operator (gawk): GNU Regexp Operators. * \ (backslash), \f escape sequence: Escape Sequences. * \ (backslash), \n escape sequence: Escape Sequences. * \ (backslash), \NNN escape sequence: Escape Sequences. * \ (backslash), \r escape sequence: Escape Sequences. * \ (backslash), \t escape sequence: Escape Sequences. * \ (backslash), \v escape sequence: Escape Sequences. * \ (backslash), \W operator (gawk): GNU Regexp Operators. * \ (backslash), \w operator (gawk): GNU Regexp Operators. * \ (backslash), \x escape sequence: Escape Sequences. * \ (backslash), \y operator (gawk): GNU Regexp Operators. * \ (backslash), as field separators: Command Line Field Separator. * \ (backslash), continuing lines and <1>: Egrep Program. * \ (backslash), continuing lines and: Statements/Lines. * \ (backslash), continuing lines and, comments and: Statements/Lines. * \ (backslash), continuing lines and, in csh <1>: Statements/Lines. * \ (backslash), continuing lines and, in csh: More Complex. * \ (backslash), gsub/gensub/sub functions and: Gory Details. * \ (backslash), in character lists: Character Lists. * \ (backslash), in escape sequences: Escape Sequences. * \ (backslash), in escape sequences, POSIX and: Escape Sequences. * \ (backslash), regexp constants: Computed Regexps. * ^ (caret) <1>: GNU Regexp Operators. * ^ (caret): Regexp Operators. * ^ (caret), ^ operator <1>: Options. * ^ (caret), ^ operator: Precedence. * ^ (caret), ^= operator <1>: Options. * ^ (caret), ^= operator <2>: Precedence. * ^ (caret), ^= operator: Assignment Ops. * ^ (caret), in character lists: Character Lists. * _ (underscore), _ C macro: Explaining gettext. * _ (underscore), in names of private variables: Library Names. * _ (underscore), translatable string: Programmer i18n. * _gr_init user-defined function: Group Functions. * _pw_init user-defined function: Passwd Functions. d17259 10 a17268 26 * account information <1>: Group Functions. * account information: Passwd Functions. * actions: Action Overview. * actions, control statements in: Statements. * actions, default: Very Simple. * actions, empty: Very Simple. * adding, features to gawk: Adding Code. * adding, fields: Changing Fields. * adding, functions to gawk: Dynamic Extensions. * advanced features, buffering: I/O Functions. * advanced features, close function: Close Files And Pipes. * advanced features, constants, values of: Nondecimal-numbers. * advanced features, data files as single record: Records. * advanced features, fixed-width data: Constant Size. * advanced features, FNR/NR variables: Auto-set. * advanced features, gawk: Advanced Features. * advanced features, gawk, BSD portals: Portal Files. * advanced features, gawk, network programming: TCP/IP Networking. * advanced features, gawk, nondecimal input data: Nondecimal Data. * advanced features, gawk, processes, communicating with: Two-way I/O. * advanced features, network connections, See Also networks, connections: Advanced Features. * advanced features, null strings, matching: Gory Details. * advanced features, operators, precedence: Increment Ops. * advanced features, piping into sh: Redirection. * advanced features, regexp constants: Assignment Ops. * Aho, Alfred <1>: Contributors. d17270 2 a17271 7 * alarm clock example program: Alarm Program. * alarm.awk program: Alarm Program. * algorithms: Basic High Level. * Alpha (DEC): Manual History. * amazing awk assembler (aaa): Glossary. * amazingly workable formatter (awf): Glossary. * ambiguity, syntactic: /= operator vs. /=.../ regexp constant: Assignment Ops. d17273 13 a17285 21 * ampersand (&), && operator: Boolean Ops. * ampersand (&), &&operator: Precedence. * ampersand (&), gsub/gensub/sub functions and: Gory Details. * AND bitwise operation: Bitwise Functions. * and Boolean-logic operator: Boolean Ops. * and function (gawk): Bitwise Functions. * ANSI: Glossary. * archeologists: Bugs. * ARGC/ARGV variables <1>: ARGC and ARGV. * ARGC/ARGV variables: Auto-set. * ARGC/ARGV variables, command-line arguments: Other Arguments. * ARGC/ARGV variables, portability and: Executable Scripts. * ARGIND variable: Auto-set. * ARGIND variable, command-line arguments: Other Arguments. * arguments, command-line <1>: Other Arguments. * arguments, command-line <2>: ARGC and ARGV. * arguments, command-line: Auto-set. * arguments, command-line, invoking awk: Command Line. * arguments, in function calls: Function Calls. * arguments, processing: Getopt Function. * arguments, retrieving: Internals. d17287 5 a17291 2 * arrays: Arrays. * arrays, as parameters to functions: Function Caveats. d17293 2 a17294 2 * arrays, associative, clearing: Internals. * arrays, associative, library functions and: Library Names. d17296 2 a17297 16 * arrays, elements, assigning: Assigning Elements. * arrays, elements, deleting: Delete. * arrays, elements, installing: Internals. * arrays, elements, order of: Scanning an Array. * arrays, elements, referencing: Reference to Elements. * arrays, elements, retrieving number of: String Functions. * arrays, for statement and: Scanning an Array. * arrays, IGNORECASE variable and: Array Intro. * arrays, indexing: Array Intro. * arrays, merging into strings: Join Function. * arrays, multidimensional: Multi-dimensional. * arrays, multidimensional, scanning: Multi-scanning. * arrays, names of: Arrays. * arrays, scanning: Scanning an Array. * arrays, sorting: Array Sorting. * arrays, sorting, IGNORECASE variable and: Array Sorting. d17299 3 a17301 3 * arrays, subscripts: Numeric Array Subscripts. * arrays, subscripts, uninitialized variables as: Uninitialized Subscripts. * artificial intelligence, gawk and: Distribution contents. d17303 2 a17304 6 * asort function (gawk) <1>: String Functions. * asort function (gawk): Array Sorting. * asort function (gawk), arrays, sorting: Array Sorting. * asorti function (gawk): String Functions. * assert function (C library): Assert Function. * assert user-defined function: Assert Function. d17307 1 a17307 5 * assignment operators, evaluation order: Assignment Ops. * assignment operators, lvalues/rvalues: Assignment Ops. * assignments as filenames: Ignoring Assigns. * assoc_clear internal function: Internals. * assoc_lookup internal function: Internals. d17309 1 a17309 12 * asterisk (*), * operator, as multiplication operator: Precedence. * asterisk (*), * operator, as regexp operator: Regexp Operators. * asterisk (*), * operator, null strings, matching: Gory Details. * asterisk (*), ** operator <1>: Options. * asterisk (*), ** operator <2>: Precedence. * asterisk (*), ** operator: Arithmetic Ops. * asterisk (*), **= operator <1>: Options. * asterisk (*), **= operator <2>: Precedence. * asterisk (*), **= operator: Assignment Ops. * asterisk (*), *= operator <1>: Precedence. * asterisk (*), *= operator: Assignment Ops. * atan2 function: Numeric Functions. d17311 21 a17331 51 * awf (amazingly workable formatter) program: Glossary. * awk language, POSIX version: Assignment Ops. * awk programs <1>: Two Rules. * awk programs <2>: Executable Scripts. * awk programs: Getting Started. * awk programs, complex: When. * awk programs, documenting <1>: Library Names. * awk programs, documenting: Comments. * awk programs, examples of: Sample Programs. * awk programs, execution of: Next Statement. * awk programs, internationalizing <1>: Programmer i18n. * awk programs, internationalizing: I18N Functions. * awk programs, lengthy: Long. * awk programs, lengthy, assertions: Assert Function. * awk programs, location of: Options. * awk programs, one-line examples: Very Simple. * awk programs, profiling: Profiling. * awk programs, profiling, enabling: Options. * awk programs, running <1>: Long. * awk programs, running: Running gawk. * awk programs, running, from shell scripts: One-shot. * awk programs, running, without input files: Read Terminal. * awk programs, shell variables in: Using Shell Variables. * awk, function of: Getting Started. * awk, gawk and <1>: This Manual. * awk, gawk and: Preface. * awk, history of: History. * awk, implementation issues, pipes: Redirection. * awk, implementations: Other Versions. * awk, implementations, limits: Getline Notes. * awk, invoking: Command Line. * awk, new vs. old: Names. * awk, new vs. old, OFMT variable: Conversion. * awk, POSIX and: Preface. * awk, POSIX and, See Also POSIX awk: Preface. * awk, regexp constants and: Typing and Comparison. * awk, See Also gawk: Preface. * awk, terms describing: This Manual. * awk, uses for <1>: When. * awk, uses for <2>: Getting Started. * awk, uses for: Preface. * awk, versions of <1>: V7/SVR3.1. * awk, versions of: Names. * awk, versions of, changes between SVR3.1 and SVR4: SVR4. * awk, versions of, changes between SVR4 and POSIX awk: POSIX. * awk, versions of, changes between V7 and SVR3.1: V7/SVR3.1. * awk, versions of, See Also Bell Laboratories awk: BTL. * awk.h file (internal): Internals. * awka compiler for awk: Other Versions. * AWKNUM internal type: Internals. * AWKPATH environment variable <1>: PC Using. d17333 7 a17339 37 * awkprof.out file: Profiling. * awksed.awk program: Simple Sed. * awkvars.out file: Options. * backslash (\) <1>: Regexp Operators. * backslash (\) <2>: Quoting. * backslash (\) <3>: Comments. * backslash (\): Read Terminal. * backslash (\), \" escape sequence: Escape Sequences. * backslash (\), \' operator (gawk): GNU Regexp Operators. * backslash (\), \/ escape sequence: Escape Sequences. * backslash (\), \< operator (gawk): GNU Regexp Operators. * backslash (\), \> operator (gawk): GNU Regexp Operators. * backslash (\), \` operator (gawk): GNU Regexp Operators. * backslash (\), \a escape sequence: Escape Sequences. * backslash (\), \b escape sequence: Escape Sequences. * backslash (\), \B operator (gawk): GNU Regexp Operators. * backslash (\), \f escape sequence: Escape Sequences. * backslash (\), \n escape sequence: Escape Sequences. * backslash (\), \NNN escape sequence: Escape Sequences. * backslash (\), \r escape sequence: Escape Sequences. * backslash (\), \t escape sequence: Escape Sequences. * backslash (\), \v escape sequence: Escape Sequences. * backslash (\), \W operator (gawk): GNU Regexp Operators. * backslash (\), \w operator (gawk): GNU Regexp Operators. * backslash (\), \x escape sequence: Escape Sequences. * backslash (\), \y operator (gawk): GNU Regexp Operators. * backslash (\), as field separators: Command Line Field Separator. * backslash (\), continuing lines and <1>: Egrep Program. * backslash (\), continuing lines and: Statements/Lines. * backslash (\), continuing lines and, comments and: Statements/Lines. * backslash (\), continuing lines and, in csh <1>: Statements/Lines. * backslash (\), continuing lines and, in csh: More Complex. * backslash (\), gsub/gensub/sub functions and: Gory Details. * backslash (\), in character lists: Character Lists. * backslash (\), in escape sequences: Escape Sequences. * backslash (\), in escape sequences, POSIX and: Escape Sequences. * backslash (\), regexp constants: Computed Regexps. d17341 6 a17346 45 * Beebe, Nelson: Acknowledgments. * Beebe, Nelson H.F.: Other Versions. * BEGIN pattern <1>: BEGIN/END. * BEGIN pattern <2>: Field Separators. * BEGIN pattern: Records. * BEGIN pattern, assert user-defined function and: Assert Function. * BEGIN pattern, Boolean patterns and: Expression Patterns. * BEGIN pattern, exit statement and: Exit Statement. * BEGIN pattern, getline and: Getline Notes. * BEGIN pattern, headings, adding: Print Examples. * BEGIN pattern, next/nextfile statements and <1>: Next Statement. * BEGIN pattern, next/nextfile statements and: I/O And BEGIN/END. * BEGIN pattern, OFS/ORS variables, assigning values to: Output Separators. * BEGIN pattern, operators and: Using BEGIN/END. * BEGIN pattern, pgawk program: Profiling. * BEGIN pattern, print statement and: I/O And BEGIN/END. * BEGIN pattern, pwcat program: Passwd Functions. * BEGIN pattern, running awk programs and: Cut Program. * BEGIN pattern, TEXTDOMAIN variable and: Programmer i18n. * beginfile user-defined function: Filetrans Function. * Bell Laboratories awk extensions: BTL. * Benzinger, Michael: Contributors. * BeOS: BeOS Installation. * Berry, Karl: Acknowledgments. * binary input/output: User-modified. * bindtextdomain function (C library): Explaining gettext. * bindtextdomain function (gawk) <1>: Programmer i18n. * bindtextdomain function (gawk): I18N Functions. * bindtextdomain function (gawk), portability and: I18N Portability. * BINMODE variable <1>: PC Using. * BINMODE variable: User-modified. * bits2str user-defined function: Bitwise Functions. * bitwise, complement: Bitwise Functions. * bitwise, operations: Bitwise Functions. * bitwise, shift: Bitwise Functions. * body, in actions: Statements. * body, in loops: While Statement. * Boolean expressions: Boolean Ops. * Boolean expressions, as patterns: Expression Patterns. * Boolean operators, See Boolean expressions: Boolean Ops. * Bourne shell, quoting rules for: Quoting. * braces ({}), actions and: Action Overview. * braces ({}), pgawk program: Profiling. * braces ({}), statements, grouping: Statements. * bracket expressions, See character lists: Regexp Operators. d17348 1 d17350 7 a17356 14 * Brennan, Michael <2>: Simple Sed. * Brennan, Michael <3>: Two-way I/O. * Brennan, Michael: Delete. * Broder, Alan J.: Contributors. * Brown, Martin <1>: Bugs. * Brown, Martin <2>: Contributors. * Brown, Martin: Acknowledgments. * BSD portals: Portal Files. * BSD-based operating systems: Glossary. * Buening, Andreas <1>: Contributors. * Buening, Andreas: Acknowledgments. * buffering, input/output <1>: Two-way I/O. * buffering, input/output: I/O Functions. * buffering, interactive vs. noninteractive: I/O Functions. d17358 2 a17359 5 * buffers, operators for: GNU Regexp Operators. * bug reports, email address, bug-gawk@@gnu.org: Bugs. * bug-gawk@@gnu.org bug reporting address: Bugs. * built-in functions: Functions. * built-in functions, evaluation order: Calling Built-in. d17361 2 a17362 3 * built-in variables, -v option, setting with: Options. * built-in variables, conveying information: Auto-set. * built-in variables, user-modifiable: User-modified. d17365 7 a17371 16 * caret (^) <1>: GNU Regexp Operators. * caret (^): Regexp Operators. * caret (^), ^ operator <1>: Options. * caret (^), ^ operator: Precedence. * caret (^), ^= operator <1>: Options. * caret (^), ^= operator <2>: Precedence. * caret (^), ^= operator: Assignment Ops. * caret (^), in character lists: Character Lists. * case keyword: Switch Statement. * case sensitivity, array indices and: Array Intro. * case sensitivity, converting case: String Functions. * case sensitivity, example programs: Library Functions. * case sensitivity, gawk: Case-sensitivity. * case sensitivity, regexps and <1>: User-modified. * case sensitivity, regexps and: Case-sensitivity. * case sensitivity, string comparisons and: User-modified. d17373 2 a17374 9 * character lists <1>: Character Lists. * character lists: Regexp Operators. * character lists, character classes: Character Lists. * character lists, collating elements: Character Lists. * character lists, collating symbols: Character Lists. * character lists, complemented: Regexp Operators. * character lists, equivalence classes: Character Lists. * character lists, non-ASCII: Character Lists. * character lists, range expressions: Character Lists. d17376 18 a17393 40 * character sets (machine character encodings): Glossary. * character sets, See Also character lists: Regexp Operators. * characters, counting: Wc Program. * characters, transliterating: Translate Program. * characters, values of as numbers: Ordinal Functions. * Chassell, Robert J.: Acknowledgments. * chdir function, implementing in gawk: Sample Library. * chem utility: Glossary. * chr user-defined function: Ordinal Functions. * Cliff random numbers: Cliff Random Function. * cliff_rand user-defined function: Cliff Random Function. * close function <1>: I/O Functions. * close function <2>: Close Files And Pipes. * close function <3>: Getline/Pipe. * close function: Getline/Variable/File. * close function, return values: Close Files And Pipes. * close function, two-way pipes and: Two-way I/O. * Close, Diane <1>: Contributors. * Close, Diane: Manual History. * collating elements: Character Lists. * collating symbols: Character Lists. * columns, aligning: Print Examples. * columns, cutting: Cut Program. * comma (,), in range patterns: Ranges. * command line, arguments <1>: Other Arguments. * command line, arguments <2>: ARGC and ARGV. * command line, arguments: Auto-set. * command line, formats: Running gawk. * command line, FS on, setting: Command Line Field Separator. * command line, invoking awk from: Command Line. * command line, options <1>: Options. * command line, options <2>: Command Line Field Separator. * command line, options: Long. * command line, options, end of: Options. * command line, variables, assigning on: Assignment Options. * command-line options, processing: Getopt Function. * command-line options, string extraction: String Extraction. * commenting: Comments. * commenting, backslash continuation and: Statements/Lines. * comp.lang.awk newsgroup: Bugs. d17395 9 a17403 22 * comparison expressions, as patterns: Expression Patterns. * comparison expressions, string vs. regexp: Typing and Comparison. * compatibility mode (gawk), extensions: POSIX/GNU. * compatibility mode (gawk), file names: Special Caveats. * compatibility mode (gawk), hexadecimal numbers: Nondecimal-numbers. * compatibility mode (gawk), octal numbers: Nondecimal-numbers. * compatibility mode (gawk), specifying: Options. * compiled programs <1>: Glossary. * compiled programs: Basic High Level. * compl function (gawk): Bitwise Functions. * complement, bitwise: Bitwise Functions. * compound statements, control statements and: Statements. * concatenating: Concatenation. * conditional expressions: Conditional Exp. * configuration option, --disable-lint: Additional Configuration Options. * configuration option, --disable-nls: Additional Configuration Options. * configuration option, --enable-portals: Additional Configuration Options. * configuration option, --enable-switch: Additional Configuration Options. * configuration option, --with-included-gettext <1>: Additional Configuration Options. * configuration option, --with-included-gettext: Gawk I18N. * configuration options, gawk: Additional Configuration Options. * constants, nondecimal: Nondecimal Data. d17405 1 d17407 14 a17420 23 * control statements: Statements. * converting, case: String Functions. * converting, dates to timestamps: Time Functions. * converting, during subscripting: Numeric Array Subscripts. * converting, numbers: Conversion. * converting, numbers, to strings: Bitwise Functions. * converting, strings to numbers: Conversion. * CONVFMT variable <1>: User-modified. * CONVFMT variable: Conversion. * CONVFMT variable, array subscripts and: Numeric Array Subscripts. * coprocesses <1>: Two-way I/O. * coprocesses: Redirection. * coprocesses, closing: Close Files And Pipes. * coprocesses, getline from: Getline/Coprocess. * cos function: Numeric Functions. * counting: Wc Program. * csh utility: Statements/Lines. * csh utility, backslash continuation and: More Complex. * csh utility, POSIXLY_CORRECT environment variable: Options. * csh utility, |& operator, comparison with: Two-way I/O. * ctime user-defined function: Function Example. * currency symbols, localization: Explaining gettext. * custom.h file: Configuration Philosophy. d17422 30 a17451 51 * cut.awk program: Cut Program. * d.c., See dark corner: Conventions. * dark corner <1>: Glossary. * dark corner <2>: Truth Values. * dark corner <3>: Assignment Ops. * dark corner <4>: Format Modifiers. * dark corner: Conventions. * dark corner, array subscripts: Uninitialized Subscripts. * dark corner, break statement: Break Statement. * dark corner, close function: Close Files And Pipes. * dark corner, command-line arguments: Assignment Options. * dark corner, continue statement: Continue Statement. * dark corner, CONVFMT variable: Conversion. * dark corner, escape sequences: Other Arguments. * dark corner, escape sequences, for metacharacters: Escape Sequences. * dark corner, exit statement: Exit Statement. * dark corner, field separators: Field Splitting Summary. * dark corner, FILENAME variable <1>: Auto-set. * dark corner, FILENAME variable: Getline Notes. * dark corner, FNR/NR variables: Auto-set. * dark corner, format-control characters: Control Letters. * dark corner, FS as null string: Single Character Fields. * dark corner, input files: Records. * dark corner, invoking awk: Command Line. * dark corner, multiline records: Multiple Line. * dark corner, NF variable, decrementing: Changing Fields. * dark corner, OFMT variable: OFMT. * dark corner, regexp constants: Using Constant Regexps. * dark corner, regexp constants, /= operator and: Assignment Ops. * dark corner, regexp constants, as arguments to user-defined functions: Using Constant Regexps. * dark corner, split function: String Functions. * dark corner, strings, storing: Records. * data, fixed-width: Constant Size. * data-driven languages: Basic High Level. * database, group, reading: Group Functions. * database, users, reading: Passwd Functions. * date utility, GNU: Time Functions. * date utility, POSIX: Time Functions. * dates, converting to timestamps: Time Functions. * dates, information related to, localization: Explaining gettext. * Davies, Stephen <1>: Bugs. * Davies, Stephen: Contributors. * dcgettext function (gawk) <1>: Programmer i18n. * dcgettext function (gawk): I18N Functions. * dcgettext function (gawk), portability and: I18N Portability. * dcngettext function (gawk) <1>: Programmer i18n. * dcngettext function (gawk): I18N Functions. * dcngettext function (gawk), portability and: I18N Portability. * deadlocks: Two-way I/O. * debugging gawk: Known Bugs. * debugging gawk, bug reports: Bugs. d17453 3 a17455 1 * default keyword: Switch Statement. d17457 1 a17457 2 * Deifik, Scott <2>: Contributors. * Deifik, Scott: Acknowledgments. d17459 1 a17459 1 * deleting elements in arrays: Delete. d17461 25 a17485 39 * differences in awk and gawk, ARGC/ARGV variables: ARGC and ARGV. * differences in awk and gawk, ARGIND variable: Auto-set. * differences in awk and gawk, array elements, deleting: Delete. * differences in awk and gawk, AWKPATH environment variable: AWKPATH Variable. * differences in awk and gawk, BEGIN/END patterns: I/O And BEGIN/END. * differences in awk and gawk, BINMODE variable <1>: PC Using. * differences in awk and gawk, BINMODE variable: User-modified. * differences in awk and gawk, close function: Close Files And Pipes. * differences in awk and gawk, ERRNO variable: Auto-set. * differences in awk and gawk, error messages: Special FD. * differences in awk and gawk, FIELDWIDTHS variable: User-modified. * differences in awk and gawk, function arguments (gawk): Calling Built-in. * differences in awk and gawk, getline command: Getline. * differences in awk and gawk, IGNORECASE variable: User-modified. * differences in awk and gawk, implementation limitations <1>: Redirection. * differences in awk and gawk, implementation limitations: Getline Notes. * differences in awk and gawk, input/output operators <1>: Redirection. * differences in awk and gawk, input/output operators: Getline/Coprocess. * differences in awk and gawk, line continuations: Conditional Exp. * differences in awk and gawk, LINT variable: User-modified. * differences in awk and gawk, match function: String Functions. * differences in awk and gawk, next/nextfile statements: Nextfile Statement. * differences in awk and gawk, print/printf statements: Format Modifiers. * differences in awk and gawk, PROCINFO array: Auto-set. * differences in awk and gawk, record separators: Records. * differences in awk and gawk, regexp constants: Using Constant Regexps. * differences in awk and gawk, regular expressions: Case-sensitivity. * differences in awk and gawk, RS/RT variables: Records. * differences in awk and gawk, RT variable: Auto-set. * differences in awk and gawk, single-character fields: Single Character Fields. * differences in awk and gawk, split function: String Functions. * differences in awk and gawk, strings: Scalar Constants. * differences in awk and gawk, strings, storing: Records. * differences in awk and gawk, strtonum function (gawk): String Functions. * differences in awk and gawk, TEXTDOMAIN variable: User-modified. * differences in awk and gawk, trunc-mod operation: Arithmetic Ops. * directories, changing: Sample Library. * directories, searching <1>: Igawk Program. * directories, searching: AWKPATH Variable. d17487 4 a17490 16 * do-while statement <1>: Do Statement. * do-while statement: Regexp Usage. * documentation, of awk programs: Library Names. * documentation, online: Manual History. * documents, searching: Dupword Program. * dollar sign ($): Regexp Operators. * dollar sign ($), $ field operator <1>: Precedence. * dollar sign ($), $ field operator: Fields. * dollar sign ($), incrementing fields and arrays: Increment Ops. * double quote (") <1>: Quoting. * double quote ("): Read Terminal. * double quote ("), regexp constants: Computed Regexps. * double-precision floating-point: Basic Data Typing. * Drepper, Ulrich: Acknowledgments. * dupnode internal function: Internals. * dupword.awk program: Dupword Program. d17492 7 a17498 10 * egrep utility <1>: Egrep Program. * egrep utility: Character Lists. * egrep.awk program: Egrep Program. * elements in arrays: Reference to Elements. * elements in arrays, assigning: Assigning Elements. * elements in arrays, deleting: Delete. * elements in arrays, order of: Scanning an Array. * elements in arrays, scanning: Scanning an Array. * email address for bug reports, bug-gawk@@gnu.org: Bugs. * EMISTERED: TCP/IP Networking. d17500 23 a17522 35 * empty strings, See null strings: Regexp Field Splitting. * END pattern: BEGIN/END. * END pattern, assert user-defined function and: Assert Function. * END pattern, backslash continuation and: Egrep Program. * END pattern, Boolean patterns and: Expression Patterns. * END pattern, exit statement and: Exit Statement. * END pattern, next/nextfile statements and <1>: Next Statement. * END pattern, next/nextfile statements and: I/O And BEGIN/END. * END pattern, operators and: Using BEGIN/END. * END pattern, pgawk program: Profiling. * END pattern, print statement and: I/O And BEGIN/END. * endfile user-defined function: Filetrans Function. * endgrent function (C library): Group Functions. * endgrent user-defined function: Group Functions. * endpwent function (C library): Passwd Functions. * endpwent user-defined function: Passwd Functions. * ENVIRON variable: Auto-set. * environment variables: Auto-set. * epoch, definition of: Glossary. * equals sign (=), = operator: Assignment Ops. * equals sign (=), == operator <1>: Precedence. * equals sign (=), == operator: Typing and Comparison. * EREs (Extended Regular Expressions): Character Lists. * ERRNO variable <1>: Internals. * ERRNO variable <2>: Auto-set. * ERRNO variable: Getline. * error handling: Special FD. * error handling, ERRNO variable and: Auto-set. * error output: Special FD. * escape processing, gsub/gensub/sub functions: Gory Details. * escape sequences: Escape Sequences. * escape sequences, unrecognized: Options. * evaluation order: Increment Ops. * evaluation order, concatenation: Concatenation. * evaluation order, functions: Calling Built-in. d17524 1 a17524 12 * exclamation point (!), ! operator <1>: Egrep Program. * exclamation point (!), ! operator <2>: Precedence. * exclamation point (!), ! operator: Boolean Ops. * exclamation point (!), != operator <1>: Precedence. * exclamation point (!), != operator: Typing and Comparison. * exclamation point (!), !~ operator <1>: Expression Patterns. * exclamation point (!), !~ operator <2>: Precedence. * exclamation point (!), !~ operator <3>: Typing and Comparison. * exclamation point (!), !~ operator <4>: Regexp Constants. * exclamation point (!), !~ operator <5>: Computed Regexps. * exclamation point (!), !~ operator <6>: Case-sensitivity. * exclamation point (!), !~ operator: Regexp Usage. d17526 12 a17537 28 * exp function: Numeric Functions. * expand utility: Very Simple. * expressions: Expressions. * expressions, as patterns: Expression Patterns. * expressions, assignment: Assignment Ops. * expressions, Boolean: Boolean Ops. * expressions, comparison: Typing and Comparison. * expressions, conditional: Conditional Exp. * expressions, matching, See comparison expressions: Typing and Comparison. * expressions, selecting: Conditional Exp. * Extended Regular Expressions (EREs): Character Lists. * extension function (gawk): Using Internal File Ops. * extensions, Bell Laboratories awk: BTL. * extensions, in gawk, not in POSIX awk: POSIX/GNU. * extensions, mawk: Other Versions. * extract.awk program: Extract Program. * extraction, of marked strings (internationalization): String Extraction. * false, logical: Truth Values. * FDL (Free Documentation License): GNU Free Documentation License. * features, adding to gawk: Adding Code. * features, advanced, See advanced features: Obsolete. * features, deprecated: Obsolete. * features, undocumented: Undocumented. * Fenlason, Jay <1>: Contributors. * Fenlason, Jay: History. * fflush function: I/O Functions. * fflush function, unsupported: Options. * field numbers: Nonconstant Fields. d17539 18 a17556 91 * field operators, dollar sign as: Fields. * field separators <1>: User-modified. * field separators: Field Separators. * field separators, choice of: Field Separators. * field separators, FIELDWIDTHS variable and: User-modified. * field separators, in multiline records: Multiple Line. * field separators, on command line: Command Line Field Separator. * field separators, POSIX and <1>: Field Splitting Summary. * field separators, POSIX and: Fields. * field separators, regular expressions as <1>: Regexp Field Splitting. * field separators, regular expressions as: Field Separators. * field separators, See Also OFS: Changing Fields. * field separators, spaces as: Cut Program. * fields <1>: Basic High Level. * fields <2>: Fields. * fields: Reading Files. * fields, adding: Changing Fields. * fields, changing contents of: Changing Fields. * fields, cutting: Cut Program. * fields, examining: Fields. * fields, number of: Fields. * fields, numbers: Nonconstant Fields. * fields, printing: Print Examples. * fields, separating: Field Separators. * fields, single-character: Single Character Fields. * FIELDWIDTHS variable <1>: User-modified. * FIELDWIDTHS variable: Constant Size. * file descriptors: Special FD. * file names, distinguishing: Auto-set. * file names, in compatibility mode: Special Caveats. * file names, standard streams in gawk: Special FD. * FILENAME variable <1>: Auto-set. * FILENAME variable: Reading Files. * FILENAME variable, getline, setting with: Getline Notes. * filenames, assignments as: Ignoring Assigns. * files, .mo: Explaining gettext. * files, .mo, converting from .po: I18N Example. * files, .mo, specifying directory of <1>: Programmer i18n. * files, .mo, specifying directory of: Explaining gettext. * files, .po <1>: Translator i18n. * files, .po: Explaining gettext. * files, .po, converting to .mo: I18N Example. * files, /dev/... special files: Special FD. * files, /inet/ (gawk): TCP/IP Networking. * files, /p (gawk): Portal Files. * files, as single records: Records. * files, awk programs in: Long. * files, awkprof.out: Profiling. * files, awkvars.out: Options. * files, closing: I/O Functions. * files, descriptors, See file descriptors: Special FD. * files, for process information: Special Process. * files, group: Group Functions. * files, information about, retrieving: Sample Library. * files, initialization and cleanup: Filetrans Function. * files, input, See input files: Read Terminal. * files, log, timestamps in: Time Functions. * files, managing: Data File Management. * files, managing, data file boundaries: Filetrans Function. * files, message object: Explaining gettext. * files, message object, converting from portable object files: I18N Example. * files, message object, specifying directory of <1>: Programmer i18n. * files, message object, specifying directory of: Explaining gettext. * files, multiple passes over: Other Arguments. * files, multiple, duplicating output into: Tee Program. * files, output, See output files: Close Files And Pipes. * files, password: Passwd Functions. * files, portable object <1>: Translator i18n. * files, portable object: Explaining gettext. * files, portable object, converting to message object files: I18N Example. * files, portable object, generating: Options. * files, portal: Portal Files. * files, processing, ARGIND variable and: Auto-set. * files, reading: Rewind Function. * files, reading, multiline records: Multiple Line. * files, searching for regular expressions: Egrep Program. * files, skipping: File Checking. * files, source, search path for: Igawk Program. * files, splitting: Split Program. * files, Texinfo, extracting programs from: Extract Program. * Fish, Fred <1>: Bugs. * Fish, Fred: Contributors. * fixed-width data: Constant Size. * flag variables <1>: Tee Program. * flag variables: Boolean Ops. * floating-point: Floating Point Issues. * floating-point, numbers: Basic Data Typing. * floating-point, numbers, AWKNUM internal type: Internals. * FNR variable <1>: Auto-set. * FNR variable: Records. * FNR variable, changing: Auto-set. d17558 18 a17575 60 * for statement, in arrays: Scanning an Array. * force_number internal function: Internals. * force_string internal function: Internals. * format specifiers, mixing regular with positional specifiers: Printf Ordering. * format specifiers, printf statement: Control Letters. * format specifiers, strftime function (gawk): Time Functions. * format strings: Basic Printf. * formats, numeric output: OFMT. * formatting output: Printf. * forward slash (/): Regexp. * forward slash (/), / operator: Precedence. * forward slash (/), /= operator <1>: Precedence. * forward slash (/), /= operator: Assignment Ops. * forward slash (/), /= operator, vs. /=.../ regexp constant: Assignment Ops. * forward slash (/), patterns and: Expression Patterns. * Free Documentation License (FDL): GNU Free Documentation License. * Free Software Foundation (FSF) <1>: Glossary. * Free Software Foundation (FSF) <2>: Getting. * Free Software Foundation (FSF): Manual History. * free_temp internal macro: Internals. * FreeBSD: Glossary. * FS variable <1>: User-modified. * FS variable: Field Separators. * FS variable, --field-separator option and: Options. * FS variable, as null string: Single Character Fields. * FS variable, as TAB character: Options. * FS variable, changing value of <1>: Known Bugs. * FS variable, changing value of: Field Separators. * FS variable, running awk programs and: Cut Program. * FS variable, setting from command line: Command Line Field Separator. * FSF (Free Software Foundation) <1>: Glossary. * FSF (Free Software Foundation) <2>: Getting. * FSF (Free Software Foundation): Manual History. * function calls: Function Calls. * functions, arrays as parameters to: Function Caveats. * functions, built-in <1>: Functions. * functions, built-in: Function Calls. * functions, built-in, adding to gawk: Dynamic Extensions. * functions, built-in, evaluation order: Calling Built-in. * functions, defining: Definition Syntax. * functions, library: Library Functions. * functions, library, assertions: Assert Function. * functions, library, associative arrays and: Library Names. * functions, library, C library: Getopt Function. * functions, library, character values as numbers: Ordinal Functions. * functions, library, Cliff random numbers: Cliff Random Function. * functions, library, command-line options: Getopt Function. * functions, library, example program for using: Igawk Program. * functions, library, group database, reading: Group Functions. * functions, library, managing data files: Data File Management. * functions, library, managing time: Gettimeofday Function. * functions, library, merging arrays into strings: Join Function. * functions, library, nextfile statement: Nextfile Function. * functions, library, rounding numbers: Round Function. * functions, library, user database, reading: Passwd Functions. * functions, names of <1>: Definition Syntax. * functions, names of: Arrays. * functions, recursive: Definition Syntax. * functions, return values, setting: Internals. * functions, string-translation: I18N Functions. d17578 18 a17595 113 * functions, user-defined, calling: Function Caveats. * functions, user-defined, counts: Profiling. * functions, user-defined, library of: Library Functions. * functions, user-defined, next/nextfile statements and <1>: Nextfile Statement. * functions, user-defined, next/nextfile statements and: Next Statement. * G-d: Acknowledgments. * Garfinkle, Scott: Contributors. * gawk, awk and <1>: This Manual. * gawk, awk and: Preface. * gawk, bitwise operations in: Bitwise Functions. * gawk, break statement in: Break Statement. * gawk, built-in variables and: Built-in Variables. * gawk, character classes and: Character Lists. * gawk, coding style in: Adding Code. * gawk, command-line options: GNU Regexp Operators. * gawk, comparison operators and: Typing and Comparison. * gawk, configuring: Configuration Philosophy. * gawk, configuring, options: Additional Configuration Options. * gawk, continue statement in: Continue Statement. * gawk, debugging: Known Bugs. * gawk, distribution: Distribution contents. * gawk, escape sequences: Escape Sequences. * gawk, extensions, disabling: Options. * gawk, features, adding: Adding Code. * gawk, features, advanced: Advanced Features. * gawk, fflush function in: I/O Functions. * gawk, field separators and: User-modified. * gawk, FIELDWIDTHS variable in: User-modified. * gawk, file names in: Special Files. * gawk, format-control characters: Control Letters. * gawk, function arguments and: Calling Built-in. * gawk, functions, adding: Dynamic Extensions. * gawk, hexadecimal numbers and: Nondecimal-numbers. * gawk, IGNORECASE variable in: User-modified. * gawk, implementation issues: Notes. * gawk, implementation issues, debugging: Compatibility Mode. * gawk, implementation issues, downward compatibility: Compatibility Mode. * gawk, implementation issues, limits: Getline Notes. * gawk, implementation issues, pipes: Redirection. * gawk, installing: Installation. * gawk, internals: Internals. * gawk, internationalization and, See internationalization: Internationalization. * gawk, interpreter, adding code to <1>: Future Extensions. * gawk, interpreter, adding code to: Using Internal File Ops. * gawk, interval expressions and: Regexp Operators. * gawk, line continuation in: Conditional Exp. * gawk, LINT variable in: User-modified. * gawk, list of contributors to: Contributors. * gawk, MS-DOS version of: PC Using. * gawk, newlines in: Statements/Lines. * gawk, next file statement in: Nextfile Statement. * gawk, nextfile statement in <1>: Nextfile Function. * gawk, nextfile statement in: Nextfile Statement. * gawk, octal numbers and: Nondecimal-numbers. * gawk, OS/2 version of: PC Using. * gawk, regexp constants and: Using Constant Regexps. * gawk, regular expressions, case sensitivity: Case-sensitivity. * gawk, regular expressions, operators: GNU Regexp Operators. * gawk, regular expressions, precedence: Regexp Operators. * gawk, See Also awk: Preface. * gawk, source code, obtaining: Getting. * gawk, splitting fields and: Constant Size. * gawk, string-translation functions: I18N Functions. * gawk, timestamps: Time Functions. * gawk, uses for: Preface. * gawk, versions of, information about, printing: Options. * gawk, word-boundary operator: GNU Regexp Operators. * General Public License (GPL): Glossary. * General Public License, See GPL: Manual History. * gensub function (gawk) <1>: String Functions. * gensub function (gawk): Using Constant Regexps. * gensub function (gawk), escape processing: Gory Details. * get_argument internal function: Internals. * getgrent function (C library): Group Functions. * getgrent user-defined function: Group Functions. * getgrgid function (C library): Group Functions. * getgrgid user-defined function: Group Functions. * getgrnam function (C library): Group Functions. * getgrnam user-defined function: Group Functions. * getgruser function (C library): Group Functions. * getgruser function, user-defined: Group Functions. * getline command: Reading Files. * getline command, _gr_init user-defined function: Group Functions. * getline command, _pw_init function: Passwd Functions. * getline command, coprocesses, using from <1>: Close Files And Pipes. * getline command, coprocesses, using from: Getline/Coprocess. * getline command, deadlock and: Two-way I/O. * getline command, explicit input with: Getline. * getline command, FILENAME variable and: Getline Notes. * getline command, return values: Getline. * getline command, variants: Getline Summary. * getopt function (C library): Getopt Function. * getopt user-defined function: Getopt Function. * getpwent function (C library): Passwd Functions. * getpwent user-defined function: Passwd Functions. * getpwnam function (C library): Passwd Functions. * getpwnam user-defined function: Passwd Functions. * getpwuid function (C library): Passwd Functions. * getpwuid user-defined function: Passwd Functions. * getservbyname function (C library): TCP/IP Networking. * gettext function (C library): Explaining gettext. * gettext library: Explaining gettext. * gettext library, locale categories: Explaining gettext. * gettimeofday user-defined function: Gettimeofday Function. * GNITS mailing list: Acknowledgments. * GNU awk, See gawk: Preface. * GNU Free Documentation License: GNU Free Documentation License. * GNU General Public License: Glossary. * GNU Lesser General Public License: Glossary. * GNU long options <1>: Options. * GNU long options: Command Line. * GNU long options, printing list of: Options. * GNU Project <1>: Glossary. a17596 8 * GNU/Linux <1>: Glossary. * GNU/Linux <2>: Atari Compiling. * GNU/Linux <3>: Additional Configuration Options. * GNU/Linux <4>: I18N Example. * GNU/Linux: Manual History. * GPL (General Public License) <1>: Glossary. * GPL (General Public License): Manual History. * GPL (General Public License), printing: Options. d17598 1 a17598 3 * Grigera, Juan <1>: Bugs. * Grigera, Juan: Contributors. * group database, reading: Group Functions. d17600 3 a17602 5 * groups, information about: Group Functions. * gsub function <1>: String Functions. * gsub function: Using Constant Regexps. * gsub function, arguments of: String Functions. * gsub function, escape processing: Gory Details. d17604 11 a17614 18 * Hankerson, Darrel <2>: Contributors. * Hankerson, Darrel: Acknowledgments. * Hartholz, Elaine: Acknowledgments. * Hartholz, Marshall: Acknowledgments. * Hasegawa, Isamu <1>: Contributors. * Hasegawa, Isamu: Acknowledgments. * hexadecimal numbers: Nondecimal-numbers. * hexadecimal, values, enabling interpretation of: Options. * histsort.awk program: History Sorting. * Hughes, Phil: Acknowledgments. * HUP signal: Profiling. * hyphen (-), - operator: Precedence. * hyphen (-), -- (decrement/increment) operators: Precedence. * hyphen (-), -- operator: Increment Ops. * hyphen (-), -= operator <1>: Precedence. * hyphen (-), -= operator: Assignment Ops. * hyphen (-), filenames beginning with: Options. * hyphen (-), in character lists: Character Lists. d17616 10 a17625 17 * id.awk program: Id Program. * if statement <1>: If Statement. * if statement: Regexp Usage. * if statement, actions, changing: Ranges. * igawk.sh program: Igawk Program. * IGNORECASE variable <1>: User-modified. * IGNORECASE variable: Case-sensitivity. * IGNORECASE variable, array sorting and: Array Sorting. * IGNORECASE variable, array subscripts and: Array Intro. * IGNORECASE variable, in example programs: Library Functions. * implementation issues, gawk: Notes. * implementation issues, gawk, debugging: Compatibility Mode. * implementation issues, gawk, limits <1>: Redirection. * implementation issues, gawk, limits: Getline Notes. * in operator <1>: Id Program. * in operator <2>: For Statement. * in operator <3>: Precedence. a17626 2 * in operator, arrays and <1>: Scanning an Array. * in operator, arrays and: Reference to Elements. d17628 1 a17628 2 * index function: String Functions. * indexing arrays: Array Intro. d17630 2 a17631 6 * input files: Reading Files. * input files, closing: Close Files And Pipes. * input files, counting elements in: Wc Program. * input files, examples: Sample Data Files. * input files, reading: Reading Files. * input files, running awk without: Read Terminal. a17632 1 * input files, variable assignments and: Other Arguments. a17634 1 * input, data, nondecimal: Nondecimal Data. d17636 2 a17637 4 * input, files, See input files: Multiple Line. * input, multiline records: Multiple Line. * input, splitting into records: Records. * input, standard <1>: Special FD. a17638 4 * input/output, binary: User-modified. * input/output, from BEGIN and END: I/O And BEGIN/END. * input/output, two-way: Two-way I/O. * insomnia, cure for: Alarm Program. d17641 2 a17642 2 * installation, beos: BeOS Installation. * installation, tandem: Tandem Installation. d17644 3 a17646 18 * installing gawk: Installation. * int function: Numeric Functions. * INT signal (MS-DOS): Profiling. * integers: Basic Data Typing. * integers, unsigned: Basic Data Typing. * interacting with other programs: I/O Functions. * internationalization <1>: I18N and L10N. * internationalization: I18N Functions. * internationalization, localization <1>: Internationalization. * internationalization, localization: User-modified. * internationalization, localization, character classes: Character Lists. * internationalization, localization, gawk and: Internationalization. * internationalization, localization, locale categories: Explaining gettext. * internationalization, localization, marked strings: Programmer i18n. * internationalization, localization, portability and: I18N Portability. * internationalizing a program: Explaining gettext. * interpreted programs <1>: Glossary. * interpreted programs: Basic High Level. d17649 3 a17651 1 * ISO: Glossary. d17653 8 a17660 12 * ISO Latin-1: Glossary. * Jacobs, Andrew: Passwd Functions. * Jaegermann, Michal <1>: Contributors. * Jaegermann, Michal: Acknowledgments. * Jedi knights: Undocumented. * join user-defined function: Join Function. * Kahrs, Ju"rgen <1>: Contributors. * Kahrs, Ju"rgen: Acknowledgments. * Kenobi, Obi-Wan: Undocumented. * Kernighan, Brian <1>: Basic Data Typing. * Kernighan, Brian <2>: Other Versions. * Kernighan, Brian <3>: Contributors. a17661 3 * Kernighan, Brian <5>: Concatenation. * Kernighan, Brian <6>: Acknowledgments. * Kernighan, Brian <7>: Conventions. d17663 22 a17684 67 * kill command, dynamic profiling: Profiling. * Knights, jedi: Undocumented. * Kwok, Conrad: Contributors. * labels.awk program: Labels Program. * languages, data-driven: Basic High Level. * LC_ALL locale category: Explaining gettext. * LC_COLLATE locale category: Explaining gettext. * LC_CTYPE locale category: Explaining gettext. * LC_MESSAGES locale category: Explaining gettext. * LC_MESSAGES locale category, bindtextdomain function (gawk): Programmer i18n. * LC_MONETARY locale category: Explaining gettext. * LC_NUMERIC locale category: Explaining gettext. * LC_RESPONSE locale category: Explaining gettext. * LC_TIME locale category: Explaining gettext. * left angle bracket (<), < operator <1>: Precedence. * left angle bracket (<), < operator: Typing and Comparison. * left angle bracket (<), < operator (I/O): Getline/File. * left angle bracket (<), <= operator <1>: Precedence. * left angle bracket (<), <= operator: Typing and Comparison. * left shift, bitwise: Bitwise Functions. * leftmost longest match: Multiple Line. * length function: String Functions. * Lesser General Public License (LGPL): Glossary. * LGPL (Lesser General Public License): Glossary. * libraries of awk functions: Library Functions. * libraries of awk functions, assertions: Assert Function. * libraries of awk functions, associative arrays and: Library Names. * libraries of awk functions, character values as numbers: Ordinal Functions. * libraries of awk functions, command-line options: Getopt Function. * libraries of awk functions, example program for using: Igawk Program. * libraries of awk functions, group database, reading: Group Functions. * libraries of awk functions, managing, data files: Data File Management. * libraries of awk functions, managing, time: Gettimeofday Function. * libraries of awk functions, merging arrays into strings: Join Function. * libraries of awk functions, nextfile statement: Nextfile Function. * libraries of awk functions, rounding numbers: Round Function. * libraries of awk functions, user database, reading: Passwd Functions. * line breaks: Statements/Lines. * line continuations: Boolean Ops. * line continuations, gawk: Conditional Exp. * line continuations, in print statement: Print Examples. * line continuations, with C shell: More Complex. * lines, blank, printing: Print. * lines, counting: Wc Program. * lines, duplicate, removing: History Sorting. * lines, matching ranges of: Ranges. * lines, skipping between markers: Ranges. * lint checking: User-modified. * lint checking, array elements: Delete. * lint checking, array subscripts: Uninitialized Subscripts. * lint checking, empty programs: Command Line. * lint checking, issuing warnings: Options. * lint checking, POSIXLY_CORRECT environment variable: Options. * lint checking, undefined functions: Function Caveats. * LINT variable: User-modified. * Linux <1>: Glossary. * Linux <2>: Atari Compiling. * Linux <3>: Additional Configuration Options. * Linux <4>: I18N Example. * Linux: Manual History. * locale categories: Explaining gettext. * localization: I18N and L10N. * localization, See internationalization, localization: I18N and L10N. * log files, timestamps in: Time Functions. * log function: Numeric Functions. * logical false/true: Truth Values. * logical operators, See Boolean expressions: Boolean Ops. d17686 2 a17687 4 * long options: Command Line. * loops: While Statement. * loops, continue statements and: For Statement. * loops, count for header: Profiling. d17689 1 a17689 10 * loops, See Also while statement: While Statement. * Lost In Space: Dynamic Extensions. * ls utility: More Complex. * lshift function (gawk): Bitwise Functions. * lvalues/rvalues: Assignment Ops. * mailing labels, printing: Labels Program. * mailing list, GNITS: Acknowledgments. * make_builtin internal function: Internals. * make_number internal function: Internals. * make_string internal function: Internals. d17691 29 a17719 50 * marked string extraction (internationalization): String Extraction. * marked strings, extracting: String Extraction. * Marx, Groucho: Increment Ops. * match function: String Functions. * match function, RSTART/RLENGTH variables: String Functions. * matching, expressions, See comparison expressions: Typing and Comparison. * matching, leftmost longest: Multiple Line. * matching, null strings: Gory Details. * mawk program: Other Versions. * McPhee, Patrick: Contributors. * memory, releasing: Internals. * memory, setting limits: Options. * message object files: Explaining gettext. * message object files, converting from portable object files: I18N Example. * message object files, specifying directory of <1>: Programmer i18n. * message object files, specifying directory of: Explaining gettext. * metacharacters, escape sequences for: Escape Sequences. * mktime function (gawk): Time Functions. * modifiers, in format specifiers: Format Modifiers. * monetary information, localization: Explaining gettext. * msgfmt utility: I18N Example. * names, arrays/variables <1>: Library Names. * names, arrays/variables: Arrays. * names, functions <1>: Library Names. * names, functions: Definition Syntax. * namespace issues <1>: Library Names. * namespace issues: Arrays. * namespace issues, functions: Definition Syntax. * nawk utility: Names. * negative zero: Floating Point Issues. * NetBSD: Glossary. * networks, programming: TCP/IP Networking. * networks, support for: Special Network. * newlines <1>: Options. * newlines <2>: Boolean Ops. * newlines: Statements/Lines. * newlines, as field separators: Field Separators. * newlines, as record separators: Records. * newlines, in dynamic regexps: Computed Regexps. * newlines, in regexp constants: Computed Regexps. * newlines, printing: Print Examples. * newlines, separating statements in actions <1>: Statements. * newlines, separating statements in actions: Action Overview. * next file statement: POSIX/GNU. * next file statement, deprecated: Obsolete. * next file statement, in gawk: Nextfile Statement. * next statement <1>: Next Statement. * next statement: Boolean Ops. * next statement, BEGIN/END patterns and: I/O And BEGIN/END. * next statement, user-defined functions and: Next Statement. d17721 18 a17738 47 * nextfile statement, BEGIN/END patterns and: I/O And BEGIN/END. * nextfile statement, implementing: Nextfile Function. * nextfile statement, in gawk: Nextfile Statement. * nextfile statement, next file statement and: Obsolete. * nextfile statement, user-defined functions and: Nextfile Statement. * nextfile user-defined function: Nextfile Function. * NF variable <1>: Auto-set. * NF variable: Fields. * NF variable, decrementing: Changing Fields. * noassign.awk program: Ignoring Assigns. * NODE internal type: Internals. * nodes, duplicating: Internals. * not Boolean-logic operator: Boolean Ops. * NR variable <1>: Auto-set. * NR variable: Records. * NR variable, changing: Auto-set. * null strings <1>: Basic Data Typing. * null strings <2>: Truth Values. * null strings <3>: Regexp Field Splitting. * null strings: Records. * null strings, array elements and: Delete. * null strings, as array subscripts: Uninitialized Subscripts. * null strings, converting numbers to strings: Conversion. * null strings, matching: Gory Details. * null strings, quoting and: Quoting. * number sign (#), #! (executable scripts): Executable Scripts. * number sign (#), #! (executable scripts), portability issues with: Executable Scripts. * number sign (#), commenting: Comments. * numbers: Internals. * numbers, as array subscripts: Numeric Array Subscripts. * numbers, as values of characters: Ordinal Functions. * numbers, Cliff random: Cliff Random Function. * numbers, converting: Conversion. * numbers, converting, to strings <1>: Bitwise Functions. * numbers, converting, to strings: User-modified. * numbers, floating-point: Basic Data Typing. * numbers, floating-point, AWKNUM internal type: Internals. * numbers, hexadecimal: Nondecimal-numbers. * numbers, NODE internal type: Internals. * numbers, octal: Nondecimal-numbers. * numbers, random: Numeric Functions. * numbers, rounding: Round Function. * numeric, constants: Scalar Constants. * numeric, output format: OFMT. * numeric, strings: Typing and Comparison. * numeric, values: Internals. * oawk utility: Names. d17740 11 a17750 17 * octal numbers: Nondecimal-numbers. * octal values, enabling interpretation of: Options. * OFMT variable <1>: User-modified. * OFMT variable <2>: Conversion. * OFMT variable: OFMT. * OFMT variable, POSIX awk and: OFMT. * OFS variable <1>: User-modified. * OFS variable <2>: Output Separators. * OFS variable: Changing Fields. * OpenBSD: Glossary. * operating systems, BSD-based <1>: Portal Files. * operating systems, BSD-based: Manual History. * operating systems, PC, gawk on: PC Using. * operating systems, PC, gawk on, installing: PC Installation. * operating systems, porting gawk to: New Ports. * operating systems, See Also GNU/Linux, PC operating systems, Unix: Installation. * operations, bitwise: Bitwise Functions. d17753 5 a17757 13 * operators, assignment, evaluation order: Assignment Ops. * operators, Boolean, See Boolean expressions: Boolean Ops. * operators, decrement/increment: Increment Ops. * operators, GNU-specific: GNU Regexp Operators. * operators, input/output <1>: Precedence. * operators, input/output <2>: Redirection. * operators, input/output <3>: Getline/Coprocess. * operators, input/output <4>: Getline/Pipe. * operators, input/output: Getline/File. * operators, logical, See Boolean expressions: Boolean Ops. * operators, precedence <1>: Precedence. * operators, precedence: Increment Ops. * operators, relational, See operators, comparison: Typing and Comparison. d17761 11 a17771 21 * operators, string-matching, for buffers: GNU Regexp Operators. * operators, word-boundary (gawk): GNU Regexp Operators. * options, command-line <1>: Options. * options, command-line <2>: Command Line Field Separator. * options, command-line: Long. * options, command-line, end of: Options. * options, command-line, invoking awk: Command Line. * options, command-line, processing: Getopt Function. * options, deprecated: Obsolete. * options, long <1>: Options. * options, long: Command Line. * options, printing list of: Options. * OR bitwise operation: Bitwise Functions. * or Boolean-logic operator: Boolean Ops. * or function (gawk): Bitwise Functions. * ord user-defined function: Ordinal Functions. * order of evaluation, concatenation: Concatenation. * ORS variable <1>: User-modified. * ORS variable: Output Separators. * output field separator, See OFS variable: Changing Fields. * output record separator, See ORS variable: Output Separators. a17773 3 * output, duplicating into files: Tee Program. * output, files, closing: Close Files And Pipes. * output, format specifier, OFMT: OFMT. d17775 2 a17776 9 * output, pipes: Redirection. * output, printing, See printing: Printing. * output, records: Output Separators. * output, standard: Special FD. * P1003.2 POSIX standard: Glossary. * param_cnt internal variable: Internals. * parameters, number of: Internals. * parentheses (): Regexp Operators. * parentheses (), pgawk program: Profiling. d17778 10 a17787 16 * patterns: Patterns and Actions. * patterns, comparison expressions as: Expression Patterns. * patterns, counts: Profiling. * patterns, default: Very Simple. * patterns, empty: Empty. * patterns, expressions as: Regexp Patterns. * patterns, ranges in: Ranges. * patterns, regexp constants as: Expression Patterns. * patterns, types of: Pattern Overview. * pawk profiling Bell Labs awk: Other Versions. * PC operating systems, gawk on: PC Using. * PC operating systems, gawk on, installing: PC Installation. * percent sign (%), % operator: Precedence. * percent sign (%), %= operator <1>: Precedence. * percent sign (%), %= operator: Assignment Ops. * period (.): Regexp Operators. d17789 10 a17798 44 * Peters, Arno: Contributors. * Peterson, Hal: Contributors. * pgawk program: Profiling. * pgawk program, awkprof.out file: Profiling. * pgawk program, dynamic profiling: Profiling. * pipes, closing: Close Files And Pipes. * pipes, input: Getline/Pipe. * pipes, output: Redirection. * plus sign (+): Regexp Operators. * plus sign (+), + operator: Precedence. * plus sign (+), ++ operator <1>: Precedence. * plus sign (+), ++ operator: Increment Ops. * plus sign (+), += operator <1>: Precedence. * plus sign (+), += operator: Assignment Ops. * plus sign (+), decrement/increment operators: Increment Ops. * portability: Escape Sequences. * portability, #! (executable scripts): Executable Scripts. * portability, ** operator and: Arithmetic Ops. * portability, **= operator and: Assignment Ops. * portability, ARGV variable: Executable Scripts. * portability, backslash continuation and: Statements/Lines. * portability, backslash in escape sequences: Escape Sequences. * portability, close function and: Close Files And Pipes. * portability, data files as single record: Records. * portability, deleting array elements: Delete. * portability, example programs: Library Functions. * portability, fflush function and: I/O Functions. * portability, functions, defining: Definition Syntax. * portability, gawk: New Ports. * portability, gettext library and: Explaining gettext. * portability, internationalization and: I18N Portability. * portability, length function: String Functions. * portability, new awk vs. old awk: Conversion. * portability, next statement in user-defined functions: Function Caveats. * portability, NF variable, decrementing: Changing Fields. * portability, operators: Increment Ops. * portability, operators, not in POSIX awk: Precedence. * portability, POSIXLY_CORRECT environment variable: Options. * portability, substr function: String Functions. * portable object files <1>: Translator i18n. * portable object files: Explaining gettext. * portable object files, converting to message object files: I18N Example. * portable object files, generating: Options. * portal files: Portal Files. a17799 4 * positional specifiers, printf statement <1>: Printf Ordering. * positional specifiers, printf statement: Format Modifiers. * positional specifiers, printf statement, mixing with regular formats: Printf Ordering. * positive zero: Floating Point Issues. d17801 17 a17817 30 * POSIX awk: This Manual. * POSIX awk, **= operator and: Assignment Ops. * POSIX awk, < operator and: Getline/File. * POSIX awk, arithmetic operators and: Arithmetic Ops. * POSIX awk, backslashes in string constants: Escape Sequences. * POSIX awk, BEGIN/END patterns: I/O And BEGIN/END. * POSIX awk, break statement and: Break Statement. * POSIX awk, changes in awk versions: POSIX. * POSIX awk, character lists and: Character Lists. * POSIX awk, character lists and, character classes: Character Lists. * POSIX awk, continue statement and: Continue Statement. * POSIX awk, CONVFMT variable and: User-modified. * POSIX awk, date utility and: Time Functions. * POSIX awk, field separators and <1>: Field Splitting Summary. * POSIX awk, field separators and: Fields. * POSIX awk, FS variable and: User-modified. * POSIX awk, function keyword in: Definition Syntax. * POSIX awk, functions and, gsub/sub: Gory Details. * POSIX awk, functions and, length: String Functions. * POSIX awk, GNU long options and: Options. * POSIX awk, interval expressions in: Regexp Operators. * POSIX awk, next/nextfile statements and: Next Statement. * POSIX awk, numeric strings and: Typing and Comparison. * POSIX awk, OFMT variable and <1>: Conversion. * POSIX awk, OFMT variable and: OFMT. * POSIX awk, period (.), using: Regexp Operators. * POSIX awk, printf format strings and: Format Modifiers. * POSIX awk, regular expressions and: Regexp Operators. * POSIX awk, timestamps and: Time Functions. * POSIX awk, | I/O operator and: Getline/Pipe. a17818 3 * POSIX, awk and: Preface. * POSIX, gawk extensions not included in: POSIX/GNU. * POSIX, programs, implementing in awk: Clones. d17820 1 a17820 2 * precedence <1>: Precedence. * precedence: Increment Ops. d17822 1 a17822 19 * print statement: Printing. * print statement, BEGIN/END patterns and: I/O And BEGIN/END. * print statement, commas, omitting: Print Examples. * print statement, I/O operators in: Precedence. * print statement, line continuations and: Print Examples. * print statement, OFMT variable and: User-modified. * print statement, See Also redirection, of output: Redirection. * print statement, sprintf function and: Round Function. * printf statement <1>: Printf. * printf statement: Printing. * printf statement, columns, aligning: Print Examples. * printf statement, format-control characters: Control Letters. * printf statement, I/O operators in: Precedence. * printf statement, modifiers: Format Modifiers. * printf statement, positional specifiers <1>: Printf Ordering. * printf statement, positional specifiers: Format Modifiers. * printf statement, positional specifiers, mixing with regular formats: Printf Ordering. * printf statement, See Also redirection, of output: Redirection. * printf statement, sprintf function and: Round Function. d17824 2 d17827 5 a17831 15 * printing, list of options: Options. * printing, mailing labels: Labels Program. * printing, unduplicated lines of text: Uniq Program. * printing, user information: Id Program. * private variables: Library Names. * process information, files for: Special Process. * processes, two-way communications with: Two-way I/O. * processing data: Basic High Level. * PROCINFO array <1>: Group Functions. * PROCINFO array <2>: Passwd Functions. * PROCINFO array <3>: Auto-set. * PROCINFO array: Special Caveats. * profiling awk programs: Profiling. * profiling awk programs, dynamically: Profiling. * profiling gawk, See pgawk program: Profiling. d17833 3 a17835 14 * programmers, attractiveness of: Two-way I/O. * programming conventions, --non-decimal-data option: Nondecimal Data. * programming conventions, ARGC/ARGV variables: Auto-set. * programming conventions, exit statement: Exit Statement. * programming conventions, function parameters: Return Statement. * programming conventions, functions, calling: Calling Built-in. * programming conventions, functions, writing: Definition Syntax. * programming conventions, gawk internals: Internal File Ops. * programming conventions, nextfile statement: Nextfile Function. * programming conventions, private variable names: Library Names. * programming language, recipe for: History. * programming languages, data-driven vs. procedural: Getting Started. * programming, basic steps: Basic High Level. * programming, concepts: Basic Concepts. d17837 4 a17840 9 * question mark (?) <1>: GNU Regexp Operators. * question mark (?): Regexp Operators. * question mark (?), ?: operator: Precedence. * QUIT signal (MS-DOS): Profiling. * quoting <1>: Comments. * quoting <2>: Long. * quoting: Read Terminal. * quoting, rules for: Quoting. * quoting, tricks for: Quoting. d17842 1 a17842 3 * rand function: Numeric Functions. * random numbers, Cliff: Cliff Random Function. * random numbers, rand/srand functions: Numeric Functions. d17844 12 a17855 23 * range expressions: Character Lists. * range patterns: Ranges. * Rankin, Pat <1>: Bugs. * Rankin, Pat <2>: Contributors. * Rankin, Pat <3>: Assignment Ops. * Rankin, Pat: Acknowledgments. * raw sockets: TCP/IP Networking. * readable data files, checking: File Checking. * readable.awk program: File Checking. * recipe for a programming language: History. * record separators <1>: User-modified. * record separators: Records. * record separators, changing: Records. * record separators, regular expressions as: Records. * record separators, with multiline records: Multiple Line. * records <1>: Basic High Level. * records: Reading Files. * records, multiline: Multiple Line. * records, printing: Print. * records, splitting input into: Records. * records, terminating: Records. * records, treating files as: Records. * recursive functions: Definition Syntax. d17858 20 a17877 19 * reference counting, sorting arrays: Array Sorting. * regexp constants <1>: Typing and Comparison. * regexp constants <2>: Regexp Constants. * regexp constants: Regexp Usage. * regexp constants, /=.../, /= operator and: Assignment Ops. * regexp constants, as patterns: Expression Patterns. * regexp constants, in gawk: Using Constant Regexps. * regexp constants, slashes vs. quotes: Computed Regexps. * regexp constants, vs. string constants: Computed Regexps. * regexp, See regular expressions: Regexp. * regular expressions: Regexp. * regular expressions as field separators: Field Separators. * regular expressions, anchors in: Regexp Operators. * regular expressions, as field separators: Regexp Field Splitting. * regular expressions, as patterns <1>: Regexp Patterns. * regular expressions, as patterns: Regexp Usage. * regular expressions, as record separators: Records. * regular expressions, case sensitivity <1>: User-modified. * regular expressions, case sensitivity: Case-sensitivity. d17879 12 a17890 47 * regular expressions, constants, See regexp constants: Regexp Usage. * regular expressions, dynamic: Computed Regexps. * regular expressions, dynamic, with embedded newlines: Computed Regexps. * regular expressions, gawk, command-line options: GNU Regexp Operators. * regular expressions, interval expressions and: Options. * regular expressions, leftmost longest match: Leftmost Longest. * regular expressions, operators <1>: Regexp Operators. * regular expressions, operators: Regexp Usage. * regular expressions, operators, for buffers: GNU Regexp Operators. * regular expressions, operators, for words: GNU Regexp Operators. * regular expressions, operators, gawk: GNU Regexp Operators. * regular expressions, operators, precedence of: Regexp Operators. * regular expressions, searching for: Egrep Program. * relational operators, See comparison operators: Typing and Comparison. * return statement, user-defined functions: Return Statement. * return values, close function: Close Files And Pipes. * rev user-defined function: Function Example. * rewind user-defined function: Rewind Function. * right angle bracket (>), > operator <1>: Precedence. * right angle bracket (>), > operator: Typing and Comparison. * right angle bracket (>), > operator (I/O): Redirection. * right angle bracket (>), >= operator <1>: Precedence. * right angle bracket (>), >= operator: Typing and Comparison. * right angle bracket (>), >> operator (I/O) <1>: Precedence. * right angle bracket (>), >> operator (I/O): Redirection. * right shift, bitwise: Bitwise Functions. * Ritchie, Dennis: Basic Data Typing. * RLENGTH variable: Auto-set. * RLENGTH variable, match function and: String Functions. * Robbins, Arnold <1>: Future Extensions. * Robbins, Arnold <2>: Bugs. * Robbins, Arnold <3>: Contributors. * Robbins, Arnold <4>: Alarm Program. * Robbins, Arnold <5>: Passwd Functions. * Robbins, Arnold <6>: Getline/Pipe. * Robbins, Arnold: Command Line Field Separator. * Robbins, Bill: Getline/Pipe. * Robbins, Harry: Acknowledgments. * Robbins, Jean: Acknowledgments. * Robbins, Miriam <1>: Passwd Functions. * Robbins, Miriam <2>: Getline/Pipe. * Robbins, Miriam: Acknowledgments. * Robinson, Will: Dynamic Extensions. * robot, the: Dynamic Extensions. * Rommel, Kai Uwe <1>: Contributors. * Rommel, Kai Uwe: Acknowledgments. * round user-defined function: Round Function. d17892 7 a17898 12 * rounding numbers: Round Function. * RS variable <1>: User-modified. * RS variable: Records. * RS variable, multiline records and: Multiple Line. * rshift function (gawk): Bitwise Functions. * RSTART variable: Auto-set. * RSTART variable, match function and: String Functions. * RT variable <1>: Auto-set. * RT variable <2>: Multiple Line. * RT variable: Records. * Rubin, Paul <1>: Contributors. * Rubin, Paul: History. d17900 12 a17911 14 * rvalues/lvalues: Assignment Ops. * scalar values: Basic Data Typing. * Schreiber, Bert: Acknowledgments. * Schreiber, Rita: Acknowledgments. * search paths <1>: VMS Running. * search paths: PC Using. * search paths, for source files <1>: VMS Running. * search paths, for source files <2>: Igawk Program. * search paths, for source files: AWKPATH Variable. * searching: String Functions. * searching, files for regular expressions: Egrep Program. * searching, for words: Dupword Program. * sed utility <1>: Glossary. * sed utility <2>: Simple Sed. d17913 5 a17917 19 * semicolon (;): Statements/Lines. * semicolon (;), AWKPATH variable and: PC Using. * semicolon (;), separating statements in actions <1>: Statements. * semicolon (;), separating statements in actions: Action Overview. * separators, field: User-modified. * separators, field, FIELDWIDTHS variable and: User-modified. * separators, field, POSIX and: Fields. * separators, for records: Records. * separators, for records, regular expressions as: Records. * separators, for statements in actions: Action Overview. * separators, record: User-modified. * separators, subscript: User-modified. * set_value internal function: Internals. * shells, piping commands into: Redirection. * shells, quoting: Using Shell Variables. * shells, quoting, rules for: Quoting. * shells, scripts: One-shot. * shells, variables: Using Shell Variables. * shift, bitwise: Bitwise Functions. d17919 7 a17925 36 * side effects <1>: Increment Ops. * side effects: Concatenation. * side effects, array indexing: Reference to Elements. * side effects, asort function: Array Sorting. * side effects, assignment expressions: Assignment Ops. * side effects, Boolean operators: Boolean Ops. * side effects, conditional expressions: Conditional Exp. * side effects, decrement/increment operators: Increment Ops. * side effects, FILENAME variable: Getline Notes. * side effects, function calls: Function Calls. * side effects, statements: Action Overview. * signals, HUP/SIGHUP: Profiling. * signals, INT/SIGINT (MS-DOS): Profiling. * signals, QUIT/SIGQUIT (MS-DOS): Profiling. * signals, USR1/SIGUSR1: Profiling. * sin function: Numeric Functions. * single quote (') <1>: Quoting. * single quote (') <2>: Long. * single quote ('): One-shot. * single quote ('), vs. apostrophe: Comments. * single quote ('), with double quotes: Quoting. * single-character fields: Single Character Fields. * single-precision floating-point: Basic Data Typing. * Skywalker, Luke: Undocumented. * sleep utility: Alarm Program. * sockets: TCP/IP Networking. * sort function, arrays, sorting: Array Sorting. * sort utility: Word Sorting. * sort utility, coprocesses and: Two-way I/O. * sorting characters in different languages: Explaining gettext. * source code, awka: Other Versions. * source code, Bell Laboratories awk: Other Versions. * source code, gawk: Gawk Distribution. * source code, mawk: Other Versions. * source code, mixing: Options. * source files, search path for: Igawk Program. d17927 1 a17927 3 * Spencer, Henry: Glossary. * split function: String Functions. * split function, array elements, deleting: Delete. d17929 5 a17933 11 * split.awk program: Split Program. * sprintf function <1>: String Functions. * sprintf function: OFMT. * sprintf function, OFMT variable and: User-modified. * sprintf function, print/printf statements and: Round Function. * sqrt function: Numeric Functions. * square brackets ([]): Regexp Operators. * srand function: Numeric Functions. * Stallman, Richard <1>: Glossary. * Stallman, Richard <2>: Contributors. * Stallman, Richard <3>: Acknowledgments. d17935 3 a17937 1 * standard input <1>: Special FD. d17939 7 a17945 13 * standard output: Special FD. * stat function, implementing in gawk: Sample Library. * statements, compound, control statements and: Statements. * statements, control, in actions: Statements. * statements, multiple: Statements/Lines. * stlen internal variable: Internals. * stptr internal variable: Internals. * stream editors <1>: Simple Sed. * stream editors: Field Splitting Summary. * strftime function (gawk): Time Functions. * string constants: Scalar Constants. * string constants, vs. regexp constants: Computed Regexps. * string extraction (internationalization): String Extraction. d17948 9 a17956 33 * strings: Internals. * strings, converting: Conversion. * strings, converting, numbers to <1>: Bitwise Functions. * strings, converting, numbers to: User-modified. * strings, empty, See null strings: Records. * strings, extracting: String Extraction. * strings, for localization: Programmer i18n. * strings, length of: Scalar Constants. * strings, merging arrays into: Join Function. * strings, NODE internal type: Internals. * strings, null: Regexp Field Splitting. * strings, numeric: Typing and Comparison. * strings, splitting: String Functions. * strtonum function (gawk): String Functions. * strtonum function (gawk), --non-decimal-data option and: Nondecimal Data. * sub function <1>: String Functions. * sub function: Using Constant Regexps. * sub function, arguments of: String Functions. * sub function, escape processing: Gory Details. * subscript separators: User-modified. * subscripts in arrays, multidimensional: Multi-dimensional. * subscripts in arrays, multidimensional, scanning: Multi-scanning. * subscripts in arrays, numbers as: Numeric Array Subscripts. * subscripts in arrays, uninitialized variables as: Uninitialized Subscripts. * SUBSEP variable: User-modified. * SUBSEP variable, multidimensional arrays: Multi-dimensional. * substr function: String Functions. * Sumner, Andrew: Other Versions. * switch statement: Switch Statement. * syntactic ambiguity: /= operator vs. /=.../ regexp constant: Assignment Ops. * system function: I/O Functions. * systime function (gawk): Time Functions. * tandem: Tandem Installation. a17957 2 * TCP/IP: TCP/IP Networking. * TCP/IP, support for: Special Network. d17959 3 a17961 30 * tee.awk program: Tee Program. * terminating records: Records. * testbits.awk program: Bitwise Functions. * Texinfo <1>: Adding Code. * Texinfo <2>: Distribution contents. * Texinfo <3>: Extract Program. * Texinfo <4>: Dupword Program. * Texinfo <5>: Library Functions. * Texinfo <6>: Sample Data Files. * Texinfo: Conventions. * Texinfo, chapter beginnings in files: Regexp Operators. * Texinfo, extracting programs from source files: Extract Program. * text, printing: Print. * text, printing, unduplicated lines of: Uniq Program. * textdomain function (C library): Explaining gettext. * TEXTDOMAIN variable <1>: Programmer i18n. * TEXTDOMAIN variable: User-modified. * TEXTDOMAIN variable, BEGIN pattern and: Programmer i18n. * TEXTDOMAIN variable, portability and: I18N Portability. * tilde (~), ~ operator <1>: Expression Patterns. * tilde (~), ~ operator <2>: Precedence. * tilde (~), ~ operator <3>: Typing and Comparison. * tilde (~), ~ operator <4>: Regexp Constants. * tilde (~), ~ operator <5>: Computed Regexps. * tilde (~), ~ operator <6>: Case-sensitivity. * tilde (~), ~ operator: Regexp Usage. * time, alarm clock example program: Alarm Program. * time, localization and: Explaining gettext. * time, managing: Gettimeofday Function. * time, retrieving: Time Functions. d17963 1 a17963 1 * timestamps, converting dates to: Time Functions. d17965 4 a17968 37 * tmp_number internal function: Internals. * tmp_string internal function: Internals. * tolower function: String Functions. * toupper function: String Functions. * tr utility: Translate Program. * translate.awk program: Translate Program. * troubleshooting, --non-decimal-data option: Options. * troubleshooting, -F option: Known Bugs. * troubleshooting, == operator: Typing and Comparison. * troubleshooting, awk uses FS not IFS: Field Separators. * troubleshooting, backslash before nonspecial character: Escape Sequences. * troubleshooting, division: Arithmetic Ops. * troubleshooting, fatal errors, field widths, specifying: Constant Size. * troubleshooting, fatal errors, printf format strings: Format Modifiers. * troubleshooting, fflush function: I/O Functions. * troubleshooting, function call syntax: Function Calls. * troubleshooting, gawk <1>: Compatibility Mode. * troubleshooting, gawk: Known Bugs. * troubleshooting, gawk, bug reports: Bugs. * troubleshooting, gawk, fatal errors, function arguments: Calling Built-in. * troubleshooting, getline function: File Checking. * troubleshooting, gsub/sub functions: String Functions. * troubleshooting, match function: String Functions. * troubleshooting, print statement, omitting commas: Print Examples. * troubleshooting, printing: Redirection. * troubleshooting, quotes with file names: Special FD. * troubleshooting, readable data files: File Checking. * troubleshooting, regexp constants vs. string constants: Computed Regexps. * troubleshooting, string concatenation: Concatenation. * troubleshooting, substr function: String Functions. * troubleshooting, system function: I/O Functions. * troubleshooting, typographical errors, global variables: Options. * true, logical: Truth Values. * Trueman, David <1>: Contributors. * Trueman, David <2>: Acknowledgments. * Trueman, David: History. * trunc-mod operation: Arithmetic Ops. d17971 2 a17972 1 * type internal variable: Internals. a17973 3 * underscore (_), _ C macro: Explaining gettext. * underscore (_), in names of private variables: Library Names. * underscore (_), translatable string: Programmer i18n. d17977 9 a17985 18 * uniq.awk program: Uniq Program. * Unix: Glossary. * Unix awk, backslashes in escape sequences: Escape Sequences. * Unix awk, close function and: Close Files And Pipes. * Unix awk, password files, field separators and: Command Line Field Separator. * Unix, awk scripts and: Executable Scripts. * unsigned integers: Basic Data Typing. * update_ERRNO internal function: Internals. * user database, reading: Passwd Functions. * user-defined, functions: User-defined. * user-defined, functions, counts: Profiling. * user-defined, variables: Variables. * user-modifiable variables: User-modified. * users, information about, printing: Id Program. * users, information about, retrieving: Passwd Functions. * USR1 signal: Profiling. * values, numeric: Basic Data Typing. * values, string: Basic Data Typing. d17987 1 a17987 34 * variables <1>: Basic Data Typing. * variables: Other Features. * variables, assigning on command line: Assignment Options. * variables, built-in <1>: Built-in Variables. * variables, built-in: Using Variables. * variables, built-in, -v option, setting with: Options. * variables, built-in, conveying information: Auto-set. * variables, flag: Boolean Ops. * variables, getline command into, using <1>: Getline/Variable/Coprocess. * variables, getline command into, using <2>: Getline/Variable/Pipe. * variables, getline command into, using <3>: Getline/Variable/File. * variables, getline command into, using: Getline/Variable. * variables, global, for library functions: Library Names. * variables, global, printing list of: Options. * variables, initializing: Using Variables. * variables, names of: Arrays. * variables, private: Library Names. * variables, setting: Options. * variables, shadowing: Definition Syntax. * variables, types of: Assignment Ops. * variables, types of, comparison expressions and: Typing and Comparison. * variables, uninitialized, as array subscripts: Uninitialized Subscripts. * variables, user-defined: Variables. * vertical bar (|): Regexp Operators. * vertical bar (|), | operator (I/O) <1>: Precedence. * vertical bar (|), | operator (I/O): Getline/Pipe. * vertical bar (|), |& I/O operator (I/O): Two-way I/O. * vertical bar (|), |& operator (I/O) <1>: Precedence. * vertical bar (|), |& operator (I/O): Getline/Coprocess. * vertical bar (|), |& operator (I/O), two-way communications: Portal Files. * vertical bar (|), || operator <1>: Precedence. * vertical bar (|), || operator: Boolean Ops. * vname internal variable: Internals. * w utility: Constant Size. a17988 1 * warnings, issuing: Options. d17990 1 a17990 2 * wc.awk program: Wc Program. * Weinberger, Peter <1>: Contributors. d17992 2 a17993 7 * while statement <1>: While Statement. * while statement: Regexp Usage. * whitespace, as field separators: Field Separators. * whitespace, functions, calling: Calling Built-in. * whitespace, newlines as: Options. * Williams, Kent: Contributors. * Woods, John: Contributors. d17996 7 a18002 33 * word-boundary operator (gawk): GNU Regexp Operators. * wordfreq.awk program: Word Sorting. * words, counting: Wc Program. * words, duplicate, searching for: Dupword Program. * words, usage counts, generating: Word Sorting. * xgettext utility: String Extraction. * XOR bitwise operation: Bitwise Functions. * xor function (gawk): Bitwise Functions. * Zaretskii, Eli: Acknowledgments. * zero, negative vs. positive: Floating Point Issues. * zerofile.awk program: Empty Files. * Zoulas, Christos: Contributors. * {} (braces), actions and: Action Overview. * {} (braces), pgawk program: Profiling. * {} (braces), statements, grouping: Statements. * | (vertical bar): Regexp Operators. * | (vertical bar), | operator (I/O) <1>: Precedence. * | (vertical bar), | operator (I/O) <2>: Redirection. * | (vertical bar), | operator (I/O): Getline/Pipe. * | (vertical bar), |& operator (I/O) <1>: Two-way I/O. * | (vertical bar), |& operator (I/O) <2>: Precedence. * | (vertical bar), |& operator (I/O) <3>: Redirection. * | (vertical bar), |& operator (I/O): Getline/Coprocess. * | (vertical bar), |& operator (I/O), pipes, closing: Close Files And Pipes. * | (vertical bar), |& operator (I/O), two-way communications: Portal Files. * | (vertical bar), || operator <1>: Precedence. * | (vertical bar), || operator: Boolean Ops. * ~ (tilde), ~ operator <1>: Expression Patterns. * ~ (tilde), ~ operator <2>: Precedence. * ~ (tilde), ~ operator <3>: Typing and Comparison. * ~ (tilde), ~ operator <4>: Regexp Constants. * ~ (tilde), ~ operator <5>: Computed Regexps. * ~ (tilde), ~ operator: Case-sensitivity. d18007 231 a18237 342 Node: Top1322 Node: Foreword26888 Node: Preface31212 Ref: Preface-Footnote-134094 Node: History34326 Node: Names36541 Ref: Names-Footnote-138016 Node: This Manual38088 Ref: This Manual-Footnote-142846 Node: Conventions42946 Node: Manual History44823 Ref: Manual History-Footnote-148271 Ref: Manual History-Footnote-248312 Node: How To Contribute48386 Node: Acknowledgments48984 Node: Getting Started52789 Node: Running gawk55160 Node: One-shot56341 Node: Read Terminal57557 Ref: Read Terminal-Footnote-159206 Node: Long59377 Node: Executable Scripts60744 Ref: Executable Scripts-Footnote-162640 Ref: Executable Scripts-Footnote-262791 Node: Comments63242 Node: Quoting65601 Node: Sample Data Files69515 Node: Very Simple72548 Node: Two Rules77148 Node: More Complex79290 Ref: More Complex-Footnote-182204 Ref: More Complex-Footnote-282652 Node: Statements/Lines82735 Ref: Statements/Lines-Footnote-187094 Node: Other Features87359 Node: When88206 Node: Regexp90173 Node: Regexp Usage91626 Node: Escape Sequences93673 Node: Regexp Operators99413 Ref: Regexp Operators-Footnote-1106515 Ref: Regexp Operators-Footnote-2106662 Node: Character Lists106760 Node: GNU Regexp Operators111229 Node: Case-sensitivity114795 Ref: Case-sensitivity-Footnote-1117813 Node: Leftmost Longest118048 Node: Computed Regexps119234 Node: Locales122641 Node: Reading Files124668 Node: Records126424 Ref: Records-Footnote-1134517 Node: Fields134554 Ref: Fields-Footnote-1137578 Node: Nonconstant Fields137664 Node: Changing Fields139860 Node: Field Separators145136 Node: Regexp Field Splitting148619 Node: Single Character Fields151075 Node: Command Line Field Separator152117 Node: Field Splitting Summary155547 Ref: Field Splitting Summary-Footnote-1158730 Node: Constant Size158831 Node: Multiple Line163306 Ref: Multiple Line-Footnote-1169011 Node: Getline169190 Node: Plain Getline171253 Node: Getline/Variable173267 Node: Getline/File174399 Node: Getline/Variable/File175714 Node: Getline/Pipe177264 Node: Getline/Variable/Pipe179317 Node: Getline/Coprocess180415 Node: Getline/Variable/Coprocess181646 Node: Getline Notes182351 Node: Getline Summary183985 Node: Printing184692 Node: Print186320 Node: Print Examples187641 Node: Output Separators190421 Node: OFMT192177 Node: Printf193527 Node: Basic Printf194441 Node: Control Letters195967 Node: Format Modifiers198654 Node: Printf Examples203656 Node: Redirection206364 Node: Special Files212947 Node: Special FD213576 Node: Special Process216593 Node: Special Network218799 Node: Special Caveats219632 Ref: Special Caveats-Footnote-1220821 Node: Close Files And Pipes221204 Ref: Close Files And Pipes-Footnote-1228105 Ref: Close Files And Pipes-Footnote-2228253 Node: Expressions228401 Node: Constants230589 Node: Scalar Constants231265 Ref: Scalar Constants-Footnote-1232111 Node: Nondecimal-numbers232293 Node: Regexp Constants235345 Node: Using Constant Regexps235809 Node: Variables238891 Node: Using Variables239542 Node: Assignment Options241043 Node: Conversion242911 Ref: Conversion-Footnote-1247679 Node: Arithmetic Ops247788 Node: Concatenation250285 Node: Assignment Ops252980 Node: Increment Ops259186 Node: Truth Values262674 Node: Typing and Comparison263719 Ref: Typing and Comparison-Footnote-1270152 Node: Boolean Ops270297 Node: Conditional Exp274291 Node: Function Calls276021 Node: Precedence278914 Node: Patterns and Actions282332 Node: Pattern Overview283385 Node: Regexp Patterns284814 Node: Expression Patterns285348 Node: Ranges288889 Node: BEGIN/END291969 Node: Using BEGIN/END292709 Ref: Using BEGIN/END-Footnote-1295428 Node: I/O And BEGIN/END295542 Node: Empty297796 Node: Using Shell Variables298095 Node: Action Overview300371 Node: Statements302723 Node: If Statement304574 Node: While Statement306064 Node: Do Statement308087 Node: For Statement309227 Node: Switch Statement312358 Node: Break Statement314216 Node: Continue Statement316264 Node: Next Statement318159 Node: Nextfile Statement320430 Node: Exit Statement323018 Node: Built-in Variables325078 Node: User-modified326168 Ref: User-modified-Footnote-1333402 Node: Auto-set333464 Ref: Auto-set-Footnote-1341317 Node: ARGC and ARGV341522 Node: Arrays345226 Node: Array Intro347133 Node: Reference to Elements351326 Node: Assigning Elements353188 Node: Array Example353650 Node: Scanning an Array355373 Node: Delete357640 Ref: Delete-Footnote-1360017 Node: Numeric Array Subscripts360074 Node: Uninitialized Subscripts362256 Node: Multi-dimensional363857 Node: Multi-scanning366870 Node: Array Sorting368478 Node: Functions371826 Node: Built-in372560 Node: Calling Built-in373525 Node: Numeric Functions375483 Ref: Numeric Functions-Footnote-1379226 Ref: Numeric Functions-Footnote-2379552 Node: String Functions379821 Ref: String Functions-Footnote-1399010 Ref: String Functions-Footnote-2399139 Ref: String Functions-Footnote-3399386 Node: Gory Details399473 Ref: Gory Details-Footnote-1406035 Ref: Gory Details-Footnote-2406086 Node: I/O Functions406293 Ref: I/O Functions-Footnote-1412864 Node: Time Functions412955 Ref: Time Functions-Footnote-1423681 Ref: Time Functions-Footnote-2423749 Ref: Time Functions-Footnote-3423907 Ref: Time Functions-Footnote-4424018 Ref: Time Functions-Footnote-5424143 Ref: Time Functions-Footnote-6424370 Node: Bitwise Functions424632 Ref: Bitwise Functions-Footnote-1429291 Node: I18N Functions429475 Node: User-defined431187 Node: Definition Syntax431963 Node: Function Example436313 Node: Function Caveats438894 Node: Return Statement442751 Node: Dynamic Typing445409 Node: Internationalization446147 Node: I18N and L10N447565 Node: Explaining gettext448245 Ref: Explaining gettext-Footnote-1453152 Ref: Explaining gettext-Footnote-2453391 Node: Programmer i18n453560 Node: Translator i18n457778 Node: String Extraction458563 Ref: String Extraction-Footnote-1459504 Node: Printf Ordering459630 Ref: Printf Ordering-Footnote-1462373 Node: I18N Portability462437 Ref: I18N Portability-Footnote-1464875 Node: I18N Example464938 Ref: I18N Example-Footnote-1467550 Node: Gawk I18N467622 Node: Advanced Features468444 Node: Nondecimal Data469837 Node: Two-way I/O471389 Ref: Two-way I/O-Footnote-1476885 Node: TCP/IP Networking476962 Node: Portal Files479381 Node: Profiling480018 Node: Invoking Gawk487644 Node: Command Line488821 Node: Options489599 Ref: Options-Footnote-1500961 Node: Other Arguments500986 Node: AWKPATH Variable503660 Ref: AWKPATH Variable-Footnote-1506394 Node: Obsolete506654 Node: Undocumented507647 Node: Known Bugs507899 Node: Library Functions508491 Ref: Library Functions-Footnote-1511470 Node: Library Names511641 Ref: Library Names-Footnote-1515107 Ref: Library Names-Footnote-2515326 Node: General Functions515412 Node: Nextfile Function516348 Node: Assert Function520713 Node: Round Function524016 Node: Cliff Random Function525528 Ref: Cliff Random Function-Footnote-1526511 Node: Ordinal Functions526582 Ref: Ordinal Functions-Footnote-1529656 Node: Join Function529872 Ref: Join Function-Footnote-1531621 Node: Gettimeofday Function531821 Node: Data File Management535543 Node: Filetrans Function536168 Node: Rewind Function539598 Node: File Checking541048 Node: Empty Files542089 Node: Ignoring Assigns544318 Node: Getopt Function545860 Ref: Getopt Function-Footnote-1556912 Node: Passwd Functions557113 Ref: Passwd Functions-Footnote-1565797 Node: Group Functions565885 Node: Sample Programs573907 Node: Running Examples574581 Node: Clones575302 Node: Cut Program576427 Node: Egrep Program586158 Ref: Egrep Program-Footnote-1593942 Node: Id Program594052 Node: Split Program597683 Node: Tee Program601150 Node: Uniq Program603821 Node: Wc Program611238 Ref: Wc Program-Footnote-1615491 Node: Miscellaneous Programs615686 Node: Dupword Program616675 Node: Alarm Program618695 Node: Translate Program623271 Ref: Translate Program-Footnote-1627526 Ref: Translate Program-Footnote-2627763 Node: Labels Program627897 Ref: Labels Program-Footnote-1631222 Node: Word Sorting631306 Node: History Sorting635593 Node: Extract Program637425 Node: Simple Sed644799 Node: Igawk Program647863 Ref: Igawk Program-Footnote-1662668 Ref: Igawk Program-Footnote-2662869 Node: Language History663007 Node: V7/SVR3.1664374 Node: SVR4666449 Node: POSIX667883 Node: BTL669388 Node: POSIX/GNU670907 Node: Contributors677998 Node: Installation681436 Node: Gawk Distribution682388 Node: Getting682867 Node: Extracting684087 Node: Distribution contents685466 Node: Unix Installation690677 Node: Quick Installation691263 Node: Additional Configuration Options692956 Node: Configuration Philosophy694905 Node: Non-Unix Installation697260 Node: Amiga Installation697842 Node: BeOS Installation698929 Node: PC Installation700073 Node: PC Binary Installation701294 Node: PC Compiling703124 Node: PC Dynamic707660 Node: PC Using710008 Node: Cygwin714608 Ref: Cygwin-Footnote-1715583 Node: VMS Installation715615 Node: VMS Compilation716134 Node: VMS Installation Details717698 Node: VMS Running719315 Node: VMS POSIX720899 Node: Unsupported722163 Node: Atari Installation722561 Node: Atari Compiling723841 Node: Atari Using725713 Node: Tandem Installation728545 Node: Bugs730216 Node: Other Versions733501 Ref: Other Versions-Footnote-1737100 Node: Notes737142 Node: Compatibility Mode737815 Node: Additions738604 Node: Adding Code739349 Node: New Ports745372 Node: Dynamic Extensions749424 Node: Internals750440 Node: Sample Library757218 Node: Internal File Description757868 Node: Internal File Ops761548 Ref: Internal File Ops-Footnote-1766964 Node: Using Internal File Ops767112 Node: Future Extensions769133 Node: Basic Concepts773214 Node: Basic High Level773952 Ref: Basic High Level-Footnote-1777979 Node: Basic Data Typing778173 Node: Floating Point Issues782605 Ref: Floating Point Issues-Footnote-1786485 Ref: Floating Point Issues-Footnote-2786538 Node: Glossary786647 Node: Copying810256 Node: GNU Free Documentation License829453 Node: Index851856 @