AWK(1) | General Commands Manual | AWK(1) |
awk
—
awk |
[-F fs]
[-v var=value]
[-safe ]
[-d [N]]
[prog | -f
filename] file ... |
awk |
-version |
awk
is the Bell Labs' implementation of the AWK
programming language as described in the The AWK Programming
Language by A. V. Aho, B. W. Kernighan, and P. J. Weinberger.
awk
scans each input
file for lines that match any of a set of patterns
specified literally in prog or in one or more files
specified as -f
filename. With
each pattern there can be an associated action that will be performed when a
line of a file matches the pattern. Each line is
matched against the pattern portion of every pattern-action statement; the
associated action is performed for each matched pattern. The file name
- means the standard input. Any
file of the form var=value is
treated as an assignment, not a filename, and is executed at the time it
would have been opened if it were a filename.
The options are as follows:
-d
[N]-f
filename-f
options may be
specified.-F
fs-mr
NNN, -mf
NNN-safe
system
() make
the program abort (with a warning message).-v
var=value-v
options may be present.-version
awk
version on standard output and
exit.An input line is normally made up of fields separated by white space, or by regular expression FS. The fields are denoted $1, $2, ..., while $0 refers to the entire line. If FS is null, the input line is split into one field per character.
A pattern-action statement has the form
pattern { action }
A missing { action } means print the line; a missing pattern always matches. Pattern-action statements are separated by newlines or semicolons.
An action is a sequence of statements. Statements are terminated by semicolons, newlines or right braces. An empty expression-list stands for $0. String constants are quoted " ", with the usual C escapes recognized within. Expressions take on string or numeric values as appropriate, and are built using the Operators (see next subsection). Variables may be scalars, array elements (denoted x[i]) or fields. Variables are initialized to the null string. Array subscripts may be any string, not necessarily numeric; this allows for a form of associative memory. Multiple subscripts such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.
awk
operators, in order of decreasing precedence, are:
(...)
$
++
--
^
**
form is also supported, and
**=
for the assignment operator).<
>
≤
≥
!=
==
~
!~
in
&&
||
?:
?
expr2
:
expr3 . If
expr1 is true, the result value is
expr2, otherwise it is expr3.
Only one of expr2 and expr3 is
evaluated.= +=
-=
*=
/= %= ^=
if
(
expression )
statement [else
statement]while
(
expression )
statementfor
(
expression ;
expression ;
expression )
statementfor
(
var in
array )
statementdo
statement while (
expression )
break
continue
delete
array [expression]delete
arrayexit
[expression]return
[expression]{
[statement ...] }
close
(expr)fflush
(expr)getline
[var]getline
returns 1 for a
successful input, 0 for end of file, and -1 for an error.getline
[var] <
file| getline
getline
; each call of
getline
returns the next line of output from
expr.next
nextfile
print
[expr-list] [>
file]print
statement prints its arguments on the
standard output (or to a file if > file
or to a
pipe if | expr is present), separated by the current
output field separator OFS, and terminated by the
output record separator ORS. Both
file and expr may be literal
names or parenthesized expressions; identical string values in different
statements denote the same open file.printf
format [,
expr-list] [>
file]atan2
(x,
y)/
y in radians. See also
atan2(3).cos
(expr)exp
(expr)int
(expr)log
(expr)rand
()sin
(expr)sqrt
(expr)srand
([expr])rand
())
and returns the previous seed.gensub
(r,
s, h,
[t])g
or
G
, then replace all matches of
r with s. Otherwise,
h is a number indicating which match of
r to replace. If no t is
supplied, $0 is used instead. Unlike
sub
() and gsub
(), the
modified string is returned as the result of the function, and the
original target is not changed. Note that the
\n sequences within replacement string
s supported by GNU awk
are
not supported at this moment.gsub
(r,
s, [t])sub
() except that all occurrences of the
regular expression are replaced; sub
() and
gsub
() return the number of replacements.index
(s,
t)length
([string])match
(s,
r)split
(s,
a, [fs])sprintf
(fmt,
expr, ...)sub
(r,
s, [t])substr
(s,
m, [n])tolower
(str)toupper
(str)awk
provides the following two functions for
obtaining time stamps and formatting them:
systime
()strftime
([format [,
timestamp]])systime
(). If
timestamp is missing, current time is used. If
format is missing, a default format equivalent to
the output of date(1) would be
used. See the specification of ANSI C
strftime(3) for the format
conversions which are supported.system
(cmd)! ||
&&
) of regular expressions and relational expressions. Regular
expressions are as in egrep(1).
Isolated regular expressions in a pattern apply to the entire line. Regular
expressions may also occur in relational expressions, using the operators
~
and !~
. /
re /
is a constant regular expression; any string (constant or
variable) may be used as a regular expression, except in the position of an
isolated regular expression in a pattern.
A pattern may consist of two patterns separated by a comma; in this case, the action is performed for all lines from an occurrence of the first pattern though an occurrence of the second.
A relational expression is one of the following:
in
array-name) in
array-namewhere a relop is any of the six relational
operators in C, and a matchop is either
~
(matches) or !~
(does not
match). A conditional is an arithmetic expression, a relational expression,
or a Boolean combination of these.
The special patterns BEGIN
and
END
may be used to capture control before the first
input line is read and after the last. BEGIN
and
END
do not combine with other patterns.
-F
fs.match
(); 0 if not match.match
(); -1 if no
match.function foo(a, b, c) { ...; return x }
Parameters are passed by value if scalar and by reference if array name; functions may be called recursively. Parameters are local to the function; all other variables are global. Thus local variables may be created by providing excess parameters in the function definition.
length($0) > 72
Print first two fields in opposite order:
{ print $2, $1 }
Same, with input fields separated by comma and/or blanks and tabs:
BEGIN { FS = ",[ \t]*|[ \t]+" } { print $2, $1 }
Add up first column, print sum and average:
{ s += $1 } END { print "sum is", s, " average is", s/NR }
Print all lines between start/stop pairs:
/start/, /stop/
Simulate echo(1):
BEGIN { # Simulate echo(1) for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i] printf "\n" exit }
Print an error message to standard error:
{ print "error!" > "/dev/stderr" }
A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Language, Addison-Wesley, 1988. ISBN 0-201-07981-X
AWK Language Programming, Edition 1.0, published by the Free Software Foundation, 1995
nawk
has been the default system
awk
since NetBSD 2.0,
replacing the previously used GNU awk
.
The scope rules for variables in functions are a botch; the syntax is worse.
May 18, 2017 | NetBSD 9.4 |