








                 AAnn IInnttrroodduuccttiioonn ttoo tthhee CC sshheellll


                           _W_i_l_l_i_a_m _J_o_y
               _(_r_e_v_i_s_e_d _f_o_r _4_._3_B_S_D _b_y _M_a_r_k _S_e_i_d_e_n_)
                    Computer Science Division
    Department of Electrical Engineering and Computer Science
               University of California, Berkeley
                   Berkeley, California 94720


                            _A_B_S_T_R_A_C_T

          _C_s_h  is  a  new  command  language interpreter for
     UNIX(R) systems.   It  incorporates  good  features  of
     other  shells  and  a  _h_i_s_t_o_r_y mechanism similar to the
     _r_e_d_o of INTERLISP.  While incorporating  many  features
     of  other  shells  which  make  writing  shell programs
     (shell scripts) easier, most of the features unique  to
     _c_s_h are designed more for the interactive UNIX user.

          UNIX users who have read a general introduction to
     the system will find a valuable  basic  explanation  of
     the  shell  here.  Simple terminal interaction with _c_s_h
     is possible after reading just  the  first  section  of
     this   document.   The  second  section  describes  the
     shell's capabilities which you can  explore  after  you
     have  begun to become acquainted with the shell.  Later
     sections introduce features which are useful,  but  not
     necessary for all users of the shell.

          Additional  information includes an appendix list-
     ing special characters of the shell and a  glossary  of
     terms and commands introduced in this manual.


IInnttrroodduuccttiioonn

     A  _s_h_e_l_l is a command language interpreter.  _C_s_h is the name
of one particular command interpreter on UNIX.  The primary  pur-
pose  of  _c_s_h  is  to translate command lines typed at a terminal
into system actions, such as invocation of other  programs.   _C_s_h
is  a user program just like any you might write.  Hopefully, _c_s_h
will be a very useful program for you  in  interacting  with  the
UNIX system.

     In  addition  to  this document, you will want to refer to a
copy of the UNIX User Reference Manual.  The _c_s_h documentation in
section  1  of the manual provides a full description of all fea-
tures of the shell and is the definitive reference for  questions
about the shell.









USD:4-2                            An Introduction to the C shell


     Many words in this document are shown in _i_t_a_l_i_c_s_.  These are
important words; names of commands, and words which have  special
meaning  in discussing the shell and UNIX.  Many of the words are
defined in a glossary at the end of this document.  If you  don't
know what is meant by a word, you should look for it in the glos-
sary.

AAcckknnoowwlleeddggeemmeennttss

     Numerous people have provided good input about previous ver-
sions  of  _c_s_h and aided in its debugging and in the debugging of
its documentation.  I would  especially  like  to  thank  Michael
Ubell  who  made  the  crucial  observation that history commands
could be done well over the word structure  of  input  text,  and
implemented  a prototype history mechanism in an older version of
the shell.  Eric Allman has also provided a large number of  use-
ful  comments on the shell, helping to unify those concepts which
are present and to identify and eliminate useless and  marginally
useful  features.   Mike  O'Brien  suggested the pathname hashing
mechanism which speeds command execution.  Jim Kulp added the job
control and directory stack primitives and added their documenta-
tion to this introduction.









































An Introduction to the C shell                            USD:4-3


11..  TTeerrmmiinnaall uussaaggee ooff tthhee sshheellll

11..11..  TThhee bbaassiicc nnoottiioonn ooff ccoommmmaannddss

     A _s_h_e_l_l in UNIX acts mostly as a medium through which  other
_p_r_o_g_r_a_m_s  are  invoked.   While it has a set of _b_u_i_l_t_i_n functions
which it performs directly, most commands cause execution of pro-
grams  that  are,  in  fact, external to the shell.  The shell is
thus distinguished from the command interpreters of other systems
both  by the fact that it is just a user program, and by the fact
that it is used almost exclusively as a  mechanism  for  invoking
other programs.

     _C_o_m_m_a_n_d_s  in the UNIX system consist of a list of strings or
_w_o_r_d_s interpreted as a _c_o_m_m_a_n_d _n_a_m_e followed by _a_r_g_u_m_e_n_t_s_.   Thus
the command

     mail bill

consists  of two words.  The first word _m_a_i_l names the command to
be executed, in this case the mail program which  sends  messages
to  other  users.   The  shell  uses  the  name of the command in
attempting to execute it for you.  It will look in  a  number  of
_d_i_r_e_c_t_o_r_i_e_s  for  a  file with the name _m_a_i_l which is expected to
contain the mail program.

     The rest of the words of the command are given as  _a_r_g_u_m_e_n_t_s
to the command itself when it is executed.  In this case we spec-
ified also the argument _b_i_l_l which is  interpreted  by  the  _m_a_i_l
program  to be the name of a user to whom mail is to be sent.  In
normal terminal usage we might use the _m_a_i_l command as follows.

     % mail bill
     I have a question about the csh documentation.
     My document seems to be missing page 5.
     Does a page five exist?
          Bill
     EOT
     %


     Here we typed a message to send to _b_i_l_l and ended this  mes-
sage  with  a  ^D  which sent an end-of-file to the mail program.
(Here and throughout this document, the notation ``^_x'' is to  be
read ``control-_x'' and represents the striking of the _x key while
the control key is held down.)  The mail program then echoed  the
characters  `EOT' and transmitted our message.  The characters `%
' were printed before and after the mail command by the shell  to
indicate that input was needed.

     After  typing  the `% ' prompt the shell was reading command
input from our terminal.   We  typed  a  complete  command  `mail
bill'.   The  shell  then executed the _m_a_i_l program with argument
_b_i_l_l and went dormant waiting  for  it  to  complete.   The  mail









USD:4-4                            An Introduction to the C shell


program  then  read input from our terminal until we signalled an
end-of-file via typing a ^D after which the  shell  noticed  that
mail had completed and signaled us that it was ready to read from
the terminal again by printing another `% ' prompt.

     This is the essential pattern of all interaction  with  UNIX
through  the shell.  A complete command is typed at the terminal,
the shell executes the command and when this execution completes,
it prompts for a new command.  If you run the editor for an hour,
the shell will patiently wait for you to finish editing and  obe-
diently prompt you again whenever you finish editing.

     An  example  of  a useful command you can execute now is the
_t_s_e_t command, which sets the default _e_r_a_s_e and _k_i_l_l characters on
your terminal - the erase character erases the last character you
typed and the kill character erases  the  entire  line  you  have
entered  so  far.   By default, the erase character is the delete
key (equivalent to `^?')  and the kill character is  `^U'.   Some
people  prefer  to  make  the  erase  character the backspace key
(equivalent to `^H').  You can make this be true by typing

     tset -e

which tells the program _t_s_e_t to set the erase character to tset's
default setting for this character (a backspace).

11..22..  FFllaagg aarrgguummeennttss

     A  useful  notion in UNIX is that of a _f_l_a_g argument.  While
many arguments to commands specify file names or user names, some
arguments  rather  specify  an optional capability of the command
which you wish to invoke.  By convention,  such  arguments  begin
with the character `-' (hyphen).  Thus the command

     ls

will  produce  a  list of the files in the current _w_o_r_k_i_n_g _d_i_r_e_c_-
_t_o_r_y.  The option _-_s is the size option, and

     ls -s

causes _l_s to also give, for each file the size  of  the  file  in
blocks of 512 characters.  The manual section for each command in
the UNIX reference manual gives the available  options  for  each
command.   The _l_s command has a large number of useful and inter-
esting options.  Most other commands have either  no  options  or
only  one or two options.  It is hard to remember options of com-
mands which are not used very frequently, so most UNIX  utilities
perform only one or two functions rather than having a large num-
ber of hard to remember options.













An Introduction to the C shell                            USD:4-5


11..33..  OOuuttppuutt ttoo ffiilleess

     Commands that normally read input or  write  output  on  the
terminal  can also be executed with this input and/or output done
to a file.

     Thus suppose we wish to save the  current  date  in  a  file
called `now'.  The command

     date

will print the current date on our terminal.  This is because our
terminal is the default _s_t_a_n_d_a_r_d _o_u_t_p_u_t for the date command  and
the  date  command  prints  the date on its standard output.  The
shell lets us _r_e_d_i_r_e_c_t the _s_t_a_n_d_a_r_d _o_u_t_p_u_t of a command through a
notation  using  the  _m_e_t_a_c_h_a_r_a_c_t_e_r  `>' and the name of the file
where output is to be placed.  Thus the command

     date > now

runs the _d_a_t_e command such that its standard output is  the  file
`now'  rather  than  the  terminal.  Thus this command places the
current date and time into the file `now'.  It  is  important  to
know  that the _d_a_t_e command was unaware that its output was going
to a file rather than to the terminal.  The shell performed  this
_r_e_d_i_r_e_c_t_i_o_n before the command began executing.

     One other thing to note here is that the file `now' need not
have existed before the _d_a_t_e  command  was  executed;  the  shell
would have created the file if it did not exist.  And if the file
did exist?  If it had existed previously these previous  contents
would  have  been  discarded!  A shell option _n_o_c_l_o_b_b_e_r exists to
prevent this from happening accidentally; it is discussed in sec-
tion 2.2.

     The  system  normally  keeps files which you create with `>'
and all other files.  Thus the default is for files to be  perma-
nent.   If  you wish to create a file which will be removed auto-
matically, you can begin its name  with  a  `#'  character,  this
`scratch'  character  denotes  the  fact  that the file will be a
scratch  file.*  The system will remove such files after a couple
of days, or sooner if file space becomes very  tight.   Thus,  in
running  the _d_a_t_e command above, we don't really want to save the
output forever, so we would more likely do

-----------
*Note that if your erase character is a `#', you  will
have to precede the `#' with a `\'.  The fact that the
`#' character is  the  old  (pre-CRT)  standard  erase
character means that it seldom appears in a file name,
and allows this convention  to  be  used  for  scratch
files.   If  you are using a CRT, your erase character
should be a ^H, as we demonstrated in section 1.1  how
this could be set up.









USD:4-6                            An Introduction to the C shell


     date > #now


11..44..  MMeettaacchhaarraacctteerrss iinn tthhee sshheellll

     The shell has a large number  of  special  characters  (like
`>')  which  indicate special functions.  We say that these nota-
tions have _s_y_n_t_a_c_t_i_c and _s_e_m_a_n_t_i_c meaning to the shell.  In  gen-
eral,  most  characters which are neither letters nor digits have
special meaning to the shell.  We shall shortly learn a means  of
_q_u_o_t_a_t_i_o_n which allows us to use _m_e_t_a_c_h_a_r_a_c_t_e_r_s without the shell
treating them in any special way.

     Metacharacters normally have effect only when the  shell  is
reading  our  input.   We  need  not  worry  about  placing shell
metacharacters in a letter we are sending via _m_a_i_l_,  or  when  we
are  typing in text or data to some other program.  Note that the
shell is only reading input  when  it  has  prompted  with  `%  '
(although we can type our input even before it prompts).

11..55..  IInnppuutt ffrroomm ffiilleess;; ppiippeelliinneess

     We  learned  above  how to _r_e_d_i_r_e_c_t the _s_t_a_n_d_a_r_d _o_u_t_p_u_t of a
command to a file.  It is also possible to redirect the  _s_t_a_n_d_a_r_d
_i_n_p_u_t  of  a  command  from  a file.  This is not often necessary
since most commands will read from a file whose name is given  as
an argument.  We can give the command

     sort < data

to  run  the  _s_o_r_t command with standard input, where the command
normally reads its input, from the file `data'.   We  would  more
likely say

     sort data

letting  the  _s_o_r_t  command open the file `data' for input itself
since this is less to type.

     We should note that if we just typed

     sort

then the sort program would sort lines from its  _s_t_a_n_d_a_r_d  _i_n_p_u_t_.
Since we did not _r_e_d_i_r_e_c_t the standard input, it would sort lines
as we typed them on the terminal until we typed a ^D to  indicate
an end-of-file.

     A most useful capability is the ability to combine the stan-
dard output of one command with the standard  input  of  another,
i.e.  to run the commands in a sequence known as a _p_i_p_e_l_i_n_e_.  For
instance the command











An Introduction to the C shell                            USD:4-7


     ls -s

normally produces a list of the files in our directory  with  the
size  of  each in blocks of 512 characters.  If we are interested
in learning which of our files is largest we  may  wish  to  have
this sorted by size rather than by name, which is the default way
in which _l_s sorts.  We could look at the many options  of  _l_s  to
see  if  there was an option to do this but would eventually dis-
cover that there is not.  Instead we can use a couple  of  simple
options  of the _s_o_r_t command, combining it with _l_s to get what we
want.

     The _-_n option of sort specifies a numeric sort  rather  than
an alphabetic sort.  Thus

     ls -s | sort -n

specifies  that  the output of the _l_s command run with the option
_-_s is to be _p_i_p_e_d to the command _s_o_r_t run with the  numeric  sort
option.   This  would give us a sorted list of our files by size,
but with the smallest first.  We could then use  the  _-_r  reverse
sort option and the _h_e_a_d command in combination with the previous
command doing

     ls -s | sort -n -r | head -5

Here we have taken a list of  our  files  sorted  alphabetically,
each  with  the size in blocks.  We have run this to the standard
input of the _s_o_r_t  command  asking  it  to  sort  numerically  in
reverse  order  (largest  first).   This output has then been run
into the command _h_e_a_d which gives us the  first  few  lines.   In
this  case  we  have asked _h_e_a_d for the first 5 lines.  Thus this
command gives us the names and sizes of our 5 largest files.

     The notation introduced above is called the _p_i_p_e  mechanism.
Commands  separated  by  `|' characters are connected together by
the shell and the standard output of each is run into  the  stan-
dard  input of the next.  The leftmost command in a pipeline will
normally take its standard input from the terminal and the right-
most will place its standard output on the terminal.  Other exam-
ples of pipelines will be given later when we discuss the history
mechanism;  one important use of pipes which is illustrated there
is in the routing of information to the line printer.

11..66..  FFiilleennaammeess

     Many commands to be executed will need the names of files as
arguments.  UNIX _p_a_t_h_n_a_m_e_s consist of a number of _c_o_m_p_o_n_e_n_t_s sep-
arated by `/'.  Each component except the last names a  directory
in  which  the  next  component resides, in effect specifying the
_p_a_t_h of directories to follow to reach the file.  Thus the  path-
name











USD:4-8                            An Introduction to the C shell


     /etc/motd

specifies  a  file in the directory `etc' which is a subdirectory
of the _r_o_o_t directory `/'.  Within this directory the file  named
is `motd' which stands for `message of the day'.  A _p_a_t_h_n_a_m_e that
begins with a slash is said to be an _a_b_s_o_l_u_t_e pathname  since  it
is  specified from the absolute top of the entire directory hier-
archy of the system (the _r_o_o_t).  _P_a_t_h_n_a_m_e_s  which  do  not  begin
with  `/'  are  interpreted  as  starting  in the current _w_o_r_k_i_n_g
_d_i_r_e_c_t_o_r_y, which is, by default, your _h_o_m_e directory and  can  be
changed  dynamically  by  the  _c_d change directory command.  Such
pathnames are said to be _r_e_l_a_t_i_v_e to the working directory  since
they  are found by starting in the working directory and descend-
ing to lower levels of directories  for  each  _c_o_m_p_o_n_e_n_t  of  the
pathname.   If  the  pathname contains no slashes at all then the
file is contained in the working directory itself and  the  path-
name  is merely the name of the file in this directory.  Absolute
pathnames have no relation to the working directory.

     Most filenames consist of a number of  alphanumeric  charac-
ters and `.'s (periods).  In fact, all printing characters except
`/' (slash) may appear in filenames.  It is inconvenient to  have
most non-alphabetic characters in filenames because many of these
have special meaning to the shell.  The character `.' (period) is
not  a  shell-metacharacter  and  is  often  used to separate the
_e_x_t_e_n_s_i_o_n of a file name from the base of the name.  Thus

     prog.c prog.o prog.errs prog.output

are four related files.  They share a _b_a_s_e portion of a  name  (a
base  portion  being  that  part  of the name that is left when a
trailing `.' and following  characters  which  are  not  `.'  are
stripped  off).   The  file  `prog.c' might be the source for a C
program, the file `prog.o' the  corresponding  object  file,  the
file  `prog.errs'  the errors resulting from a compilation of the
program and the file `prog.output' the output of  a  run  of  the
program.

     If  we  wished to refer to all four of these files in a com-
mand, we could use the notation

     prog.*

This expression is expanded by the shell, before the  command  to
which  it  is an argument is executed, into a list of names which
begin with `prog.'.  The character `*' here matches any  sequence
(including the empty sequence) of characters in a file name.  The
names which match are alphabetically sorted  and  placed  in  the
_a_r_g_u_m_e_n_t _l_i_s_t of the command.  Thus the command

     echo prog.*

will echo the names










An Introduction to the C shell                            USD:4-9


     prog.c prog.errs prog.o prog.output

Note  that  the  names  are in sorted order here, and a different
order than we listed them above.  The _e_c_h_o command receives  four
words  as  arguments,  even  though  we only typed one word as as
argument directly.  The four words  were  generated  by  _f_i_l_e_n_a_m_e
_e_x_p_a_n_s_i_o_n of the one input word.

     Other  notations  for _f_i_l_e_n_a_m_e _e_x_p_a_n_s_i_o_n are also available.
The character `?' matches any single  character  in  a  filename.
Thus

     echo ? ?? ???

will  echo  a  line  of filenames; first those with one character
names, then those with two character  names,  and  finally  those
with  three  character  names.   The names of each length will be
independently sorted.

     Another mechanism  consists  of  a  sequence  of  characters
between  `[' and `]'.  This metasequence matches any single char-
acter from the enclosed set.  Thus

     prog.[co]

will match

     prog.c prog.o

in the example above.  We can also place two characters around  a
`-' in this notation to denote a range.  Thus

     chap.[1-5]

might match files

     chap.1 chap.2 chap.3 chap.4 chap.5

if they existed.  This is shorthand for

     chap.[12345]

and otherwise equivalent.

     An  important  point  to  note is that if a list of argument
words to a command (an _a_r_g_u_m_e_n_t _l_i_s_t_) contains filename expansion
syntax,  and if this filename expansion syntax fails to match any
existing file names, then the shell considers this to be an error
and prints a diagnostic

     No match.

and does not execute the command.










USD:4-10                           An Introduction to the C shell


     Another  very important point is that files with the charac-
ter `.' at the beginning are treated specially.  Neither  `*'  or
`?'  or the `[' `]' mechanism will match it.  This prevents acci-
dental matching of the filenames `.' and  `..'   in  the  working
directory  which  have  special meaning to the system, as well as
other files such as _._c_s_h_r_c which are not  normally  visible.   We
will discuss the special role of the file _._c_s_h_r_c later.

     Another  filename  expansion  mechanism  gives access to the
pathname of the _h_o_m_e directory of  other  users.   This  notation
consists  of the character `~' (tilde) followed by another user's
login name.  For instance the word `~bill' would map to the path-
name   `/usr/bill'   if   the   home  directory  for  `bill'  was
`/usr/bill'.  Since, on  large  systems,  users  may  have  login
directories  scattered over many different disk volumes with dif-
ferent prefix directory names, this notation  provides  a  conve-
nient way of accessing the files of other users.

     A  special  case  of  this notation consists of a `~' alone,
e.g. `~/mbox'.  This notation is expanded by the shell  into  the
file  `mbox'  in  your _h_o_m_e directory, i.e. into `/usr/bill/mbox'
for me on Ernie Co-vax, the UCB Computer Science  Department  VAX
machine, where this document was prepared.  This can be very use-
ful if you have used _c_d to change to another directory  and  have
found a file you wish to copy using _c_p_.  If I give the command

     cp thatfile ~

the shell will expand this command to

     cp thatfile /usr/bill

since my home directory is /usr/bill.

     There  also  exists a mechanism using the characters `{' and
`}' for abbreviating a set of words which have common  parts  but
cannot  be  abbreviated  by the above mechanisms because they are
not files, are the names of files which do not yet exist, are not
thus  conveniently  described.   This mechanism will be described
much later, in section 4.2, as it is used less frequently.

11..77..  QQuuoottaattiioonn

     We have already seen a number of metacharacters used by  the
shell.  These metacharacters pose a problem in that we cannot use
them directly as parts of words.  Thus the command

     echo *

will not echo the character `*'.  It will either echo  an  sorted
list  of filenames in the current _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y_, or print the
message `No match' if there are no files in  the  working  direc-
tory.










An Introduction to the C shell                           USD:4-11


     The  recommended  mechanism for placing characters which are
neither numbers, digits, `/', `.' or `-' in an argument word to a
command  is  to  enclose it with single quotation characters `'',
i.e.

     echo '*'

There is one special character `!' which is used by  the  _h_i_s_t_o_r_y
mechanism  of the shell and which cannot be _e_s_c_a_p_e_d by placing it
within `'' characters.  It and the character `''  itself  can  be
preceded by a single `\' to prevent their special meaning.  Thus

     echo \'\!

prints

     '!

These two mechanisms suffice to place any printing character into
a word which is an argument to a shell command.  They can be com-
bined, as in

     echo \''*'

which prints

     '*

since  the  first  `\'  escaped  the  first  `''  and the `*' was
enclosed between `'' characters.

11..88..  TTeerrmmiinnaattiinngg ccoommmmaannddss

     When you are executing a command and the  shell  is  waiting
for  it  to  complete there are several ways to force it to stop.
For instance if you type the command

     cat /etc/passwd

the system will print a copy of a list of all users of the system
on your terminal.  This is likely to continue for several minutes
unless you stop it.  You can send an INTERRUPT _s_i_g_n_a_l to the  _c_a_t
command  by typing ^C on your terminal.*  Since _c_a_t does not take
any precautions to avoid or  otherwise  handle  this  signal  the
INTERRUPT will cause it to terminate.  The shell notices that _c_a_t
has terminated and prompts you again  with  `%  '.   If  you  hit
INTERRUPT  again,  the shell will just repeat its prompt since it
handles INTERRUPT signals and chooses to continue to execute com-
mands  rather than terminating like _c_a_t did, which would have the
effect of logging you out.
-----------
*On  some older Unix systems the DEL or RUBOUT key has
the same effect. "stty all" will tell you the INTR key
value.









USD:4-12                           An Introduction to the C shell


     Another way in which many programs terminate  is  when  they
get an end-of-file from their standard input.  Thus the _m_a_i_l pro-
gram in the first example above was terminated when we typed a ^D
which  generates  an  end-of-file  from  the standard input.  The
shell also  terminates  when  it  gets  an  end-of-file  printing
`logout';  UNIX  then  logs you off the system.  Since this means
that typing too many ^D's can accidentally log us off, the  shell
has  a mechanism for preventing this.  This _i_g_n_o_r_e_e_o_f option will
be discussed in section 2.2.

     If a command has its standard input redirected from a  file,
then  it  will normally terminate when it reaches the end of this
file.  Thus if we execute

     mail bill < prepared.text

the mail command will terminate without our typing a ^D.  This is
because it read to the end-of-file of our file `prepared.text' in
which we placed a message for `bill' with an editor program.   We
could also have done

     cat prepared.text | mail bill

since  the  _c_a_t  command would then have written the text through
the pipe to the standard input of the mail command.  When the _c_a_t
command  completed  it  would  have  terminated, closing down the
pipeline and the _m_a_i_l command would have received an  end-of-file
from  it  and  terminated.  Using a pipe here is more complicated
than redirecting input so we would  more  likely  use  the  first
form.   These commands could also have been stopped by sending an
INTERRUPT.

     Another possibility for stopping a command is to suspend its
execution  temporarily, with the possibility of continuing execu-
tion later.  This is done by sending a STOP signal via  typing  a
^Z.   This  signal  causes  all  commands running on the terminal
(usually one but more if a pipeline is executing) to become  sus-
pended.   The  shell  notices  that the command(s) have been sus-
pended, types `Stopped' and then prompts for a new command.   The
previously  executing  command  has been suspended, but otherwise
unaffected by the STOP signal.  Any other commands  can  be  exe-
cuted  while  the  original  command remains suspended.  The sus-
pended command can be continued using  the  _f_g  command  with  no
arguments.   The shell will then retype the command to remind you
which command is being continued, and cause the command to resume
execution.   Unless  any input files in use by the suspended com-
mand have been changed in the meantime,  the  suspension  has  no
effect  whatsoever on the execution of the command.  This feature
can be very useful during editing,  when  you  need  to  look  at
another  file before continuing. An example of command suspension
follows.












An Introduction to the C shell                           USD:4-13


     % mail harold
     Someone just copied a big file into my directory and its name is
     ^Z
     Stopped
     % ls
     funnyfile
     prog.c
     prog.o
     % jobs
     [1]  + Stopped   mail harold
     % fg
     mail harold
     funnyfile. Do you know who did it?
     EOT
     %

In this example someone was sending a message to Harold and  for-
got  the name of the file he wanted to mention.  The mail command
was suspended by typing ^Z.  When the shell noticed that the mail
program  was suspended, it typed `Stopped' and prompted for a new
command.  Then the _l_s command was typed to find out the  name  of
the file.  The _j_o_b_s command was run to find out which command was
suspended. At this time the _f_g command was typed to continue exe-
cution  of  the mail program.  Input to the mail program was then
continued and ended with a ^D which indicated the end of the mes-
sage  at which time the mail program typed EOT.  The _j_o_b_s command
will show which commands are suspended.  The ^Z  should  only  be
typed  at  the  beginning of a line since everything typed on the
current line is discarded when a signal is  sent  from  the  key-
board.   This  also happens on INTERRUPT, and QUIT signals.  More
information on suspending jobs and controlling them is  given  in
section 2.6.

     If  you  write  or run programs which are not fully debugged
then it may be necessary  to  stop  them  somewhat  ungracefully.
This  can be done by sending them a QUIT signal, sent by typing a
^\.  This will usually provoke the shell  to  produce  a  message
like:

     Quit (Core dumped)

indicating  that a file `core' has been created containing infor-
mation about the running program's state when it  terminated  due
to  the QUIT signal.  You can examine this file yourself, or for-
ward information to the maintainer of the program telling him/her
where the _c_o_r_e _f_i_l_e is.

     If you run background commands (as explained in section 2.6)
then these commands will ignore INTERRUPT and QUIT signals at the
terminal.   To stop them you must use the _k_i_l_l command.  See sec-
tion 2.6 for an example.

     If you want to examine the output of a command without  hav-
ing it move off the screen as the output of the









USD:4-14                           An Introduction to the C shell


     cat /etc/passwd

command will, you can use the command

     more /etc/passwd

The  _m_o_r_e  program pauses after each complete screenful and types
`--More--' at which point you can hit  a  space  to  get  another
screenful,  a  return to get another line, a `?' to get some help
on other commands, or a `q' to end the  _m_o_r_e  program.   You  can
also use more as a filter, i.e.

     cat /etc/passwd | more

works just like the more simple more command above.

     For  stopping  output of commands not involving _m_o_r_e you can
use the ^S key to stop the typeout.  The typeout will resume when
you  hit  ^Q or any other key, but ^Q is normally used because it
only restarts the output and does not become input to the program
which is running.  This works well on low-speed terminals, but at
9600 baud it is hard to type ^S and ^Q fast  enough  to  paginate
the output nicely, and a program like _m_o_r_e is usually used.

     An  additional  possibility  is  to  use the ^O flush output
character; when this character is typed, all output from the cur-
rent  command  is thrown away (quickly) until the next input read
occurs or until the next shell prompt.  This can be used to allow
a command to complete without having to suffer through the output
on a slow terminal; ^O is a toggle, so flushing can be turned off
by typing ^O again while output is being flushed.

11..99..  WWhhaatt nnooww??

     We  have so far seen a number of mechanisms of the shell and
learned a lot about the way in which it operates.  The  remaining
sections will go yet further into the internals of the shell, but
you will surely want to try using the shell  before  you  go  any
further.  To try it you can log in to UNIX and type the following
command to the system:

     chsh myname /bin/csh

Here `myname' should be replaced by the name  you  typed  to  the
system  prompt  of `login:' to get onto the system.  Thus I would
use `chsh bill /bin/csh'.  YYoouu oonnllyy hhaavvee  ttoo  ddoo  tthhiiss  oonnccee;;  iitt
ttaakkeess  eeffffeecctt aatt nneexxtt llooggiinn..  You are now ready to try using _c_s_h_.

     Before you do the `chsh' command, the shell  you  are  using
when  you log into the system is `/bin/sh'.  In fact, much of the
above discussion is applicable to `/bin/sh'.   The  next  section
will  introduce  many  features  particular  to _c_s_h so you should
change your shell to _c_s_h before you begin reading it.










An Introduction to the C shell                           USD:4-15


22..  DDeettaaiillss oonn tthhee sshheellll ffoorr tteerrmmiinnaall uusseerrss

22..11..  SShheellll ssttaarrttuupp aanndd tteerrmmiinnaattiioonn

     When you login, the shell is started by the system  in  your
_h_o_m_e  directory and begins by reading commands from a file _._c_s_h_r_c
in this directory.  All shells which you may  start  during  your
terminal  session  will  read  from this file.  We will later see
what kinds of commands are usefully placed  there.   For  now  we
need not have this file and the shell does not complain about its
absence.

     A _l_o_g_i_n _s_h_e_l_l, executed after you login to the system, will,
after  it  reads  commands from _._c_s_h_r_c_, read commands from a file
_._l_o_g_i_n also in your home directory.  This file contains  commands
which  you wish to do each time you login to the UNIX system.  My
_._l_o_g_i_n file looks something like:

     set ignoreeof
     set mail=(/var/mail/bill)
     echo "${prompt}users" ; users
     alias ts \
          'set noglob ; eval `tset -s -m dialup:c100rv4pna -m plugboard:?hp2621nl *`';
     ts; stty intr ^C kill ^U crt
     set time=15 history=10
     msgs -f
     if (-e $mail) then
          echo "${prompt}mail"
          mail
     endif


     This file contains several commands to be executed  by  UNIX
each  time  I  login.  The first is a _s_e_t command which is inter-
preted directly  by  the  shell.   It  sets  the  shell  variable
_i_g_n_o_r_e_e_o_f  which  causes the shell to not log me off if I hit ^D.
Rather, I use the _l_o_g_o_u_t command to log off of  the  system.   By
setting  the _m_a_i_l variable, I ask the shell to watch for incoming
mail to me.  Every 5 minutes the shell looks for  this  file  and
tells  me if more mail has arrived there.  An alternative to this
is to put the command

     biff y

in place of this _s_e_t_; this will cause me to be  notified  immedi-
ately  when  mail arrives, and to be shown the first few lines of
the new message.

     Next I set the shell variable `time'  to  `15'  causing  the
shell  to  automatically  print out statistics lines for commands
which execute for at least 15 seconds of CPU time.  The  variable
`history' is set to 10 indicating that I want the shell to remem-
ber the last 10 commands I type in its _h_i_s_t_o_r_y  _l_i_s_t,  (described
later).









USD:4-16                           An Introduction to the C shell


     I  create  an  _a_l_i_a_s ``ts'' which executes a _t_s_e_t(1) command
setting up the modes of the terminal.   The  parameters  to  _t_s_e_t
indicate  the kinds of terminal which I usually use when not on a
hardwired port.  I then execute ``ts'' and also use the _s_t_t_y com-
mand  to  change  the interrupt character to ^C and the line kill
character to ^U.

     I then run the `msgs' program, which provides  me  with  any
system  messages  which  I  have not seen before; the `-f' option
here prevents it from telling me anything if  there  are  no  new
messages.   Finally,  if  my  mailbox file exists, then I run the
`mail' program to process my mail.

     When the `mail' and `msgs' programs finish, the  shell  will
finish  processing my _._l_o_g_i_n file and begin reading commands from
the terminal, prompting for each with `% '.  When I log  off  (by
giving the _l_o_g_o_u_t command) the shell will print `logout' and exe-
cute commands from the file `.logout' if it  exists  in  my  home
directory.  After that the shell will terminate and UNIX will log
me off the system.  If the system  is  not  going  down,  I  will
receive  a  new  login  message.  In any case, after the `logout'
message the shell is committed to terminating and  will  take  no
further input from my terminal.

22..22..  SShheellll vvaarriiaabblleess

     The  shell  maintains  a set of _v_a_r_i_a_b_l_e_s_.  We saw above the
variables _h_i_s_t_o_r_y and _t_i_m_e which had values `10'  and  `15'.   In
fact,  each  shell variable has as value an array of zero or more
_s_t_r_i_n_g_s_.  Shell variables may be assigned values by the set  com-
mand.   It  has several forms, the most useful of which was given
above and is

     set name=value


     Shell variables may be used to store values which are to  be
used  in  commands  later  through a substitution mechanism.  The
shell variables most  commonly  referenced  are,  however,  those
which  the  shell  itself  refers  to.  By changing the values of
these variables one can  directly  affect  the  behavior  of  the
shell.

     One  of  the  most important variables is the variable _p_a_t_h_.
This variable contains a sequence of directory  names  where  the
shell  searches  for commands.  The _s_e_t command with no arguments
shows the value of all variables currently  defined  (we  usually
say  _s_e_t_) in the shell.  The default value for path will be shown
by _s_e_t to be














An Introduction to the C shell                           USD:4-17


     % set
     argv   ()
     cwd    /usr/bill
     home   /usr/bill
     path   (. /usr/ucb /bin /usr/bin)
     prompt %
     shell  /bin/csh
     status 0
     term   c100rv4pna
     user   bill
     %

This output indicates that the variable path points to  the  cur-
rent  directory  `.'  and then `/usr/ucb', `/bin' and `/usr/bin'.
Commands which you may write might be in `.' (usually one of your
directories).  Commands developed at Berkeley, live in `/usr/ucb'
while commands developed at Bell Laboratories live in `/bin'  and
`/usr/bin'.

     A number of locally developed programs on the system live in
the directory `/usr/local'.  If we wish that all shells which  we
invoke to have access to these new programs we can place the com-
mand

     set path=(. /usr/ucb /bin /usr/bin /usr/local)

in our file _._c_s_h_r_c in our home directory.   Try  doing  this  and
then logging out and back in and do

     set

again to see that the value assigned to _p_a_t_h has changed.

     One  thing you should be aware of is that the shell examines
each directory which you insert into  your  path  and  determines
which  commands  are  contained  there.   Except  for the current
directory `.', which the shell treats specially, this means  that
if  commands  are  added to a directory in your search path after
you have started the shell, they will not necessarily be found by
the  shell.  If you wish to use a command which has been added in
this way, you should give the command

     rehash

to the shell, which will cause it to recompute its internal table
of  command  locations, so that it will find the newly added com-
mand.  Since the shell has to look in the current  directory  `.'
on  each command, placing it at the end of the path specification
usually works equivalently and reduces overhead.

-----------
  [+] Another  directory  that  might  interest you is
/usr/new, which contains many useful  user-contributed
programs provided with Berkeley Unix.









USD:4-18                           An Introduction to the C shell


     Other useful built in variables are the variable _h_o_m_e  which
shows  your home directory, _c_w_d which contains your current work-
ing directory, the variable _i_g_n_o_r_e_e_o_f which can be  set  in  your
_._l_o_g_i_n  file  to  tell  the shell not to exit when it receives an
end-of-file from a terminal (as described above).   The  variable
`ignoreeof'  is one of several variables which the shell does not
care about the value of, only whether  they  are  _s_e_t  or  _u_n_s_e_t_.
Thus to set this variable you simply do

     set ignoreeof

and to unset it do

     unset ignoreeof

These give the variable `ignoreeof' no value, but none is desired
or required.

     Finally, some other built-in shell variables of use are  the
variables _n_o_c_l_o_b_b_e_r and _m_a_i_l_.  The metasyntax

     > filename

which  redirects  the standard output of a command will overwrite
and destroy the previous contents of the named file.  In this way
you  may accidentally overwrite a file which is valuable.  If you
would prefer that the shell not overwrite files in this  way  you
can

     set noclobber

in your _._l_o_g_i_n file.  Then trying to do

     date > now

would  cause  a  diagnostic  if `now' existed already.  You could
type

     date >!  now

if you really wanted to overwrite the  contents  of  `now'.   The
`>!'  is a special metasyntax indicating that clobbering the file
is ok.[+]

22..33..  TThhee sshheellll''ss hhiissttoorryy lliisstt

     The  shell  can maintain a _h_i_s_t_o_r_y _l_i_s_t into which it places
the words of previous commands.  It is possible to use a notation
to reuse commands or words from commands in forming new commands.
-----------
[+]The space between the `!' and  the  word  `now'  is
critical here, as `!now' would be an invocation of the
_h_i_s_t_o_r_y  mechanism,  and  have  a  totally   different
effect.









An Introduction to the C shell                           USD:4-19


This mechanism can be used to repeat previous commands or to cor-
rect minor typing mistakes in commands.

     The  following figure gives a sample session involving typi-
cal usage of the history mechanism of the shell.  In this example
we have a very simple C program which has a bug (or two) in it in
the file `bug.c', which we `cat' out on our  terminal.   We  then
try  to  run the C compiler on it, referring to the file again as
`!$', meaning the last argument to the  previous  command.   Here
the  `!'  is  the history mechanism invocation metacharacter, and
the `$' stands for the last argument, by analogy to  `$'  in  the
editor  which  stands  for the end of the line.  The shell echoed
the command, as it would have been typed without use of the  his-
tory  mechanism,  and  then executed it.  The compilation yielded
error diagnostics so we now run the editor on the  file  we  were
trying  to  compile,  fix  the bug, and run the C compiler again,
this time referring to this command simply as `!c', which repeats
the  last  command  which  started with the letter `c'.  If there
were other commands starting with `c' done recently we could have
said `!cc' or even `!cc:p' which would have printed the last com-
mand starting with `cc' without executing it.

     After this recompilation, we ran the resulting `a.out' file,
and then noting that there still was a bug, ran the editor again.
After fixing the program we ran the C compiler again, but  tacked
onto  the command an extra `-o bug' telling the compiler to place
the resultant binary in the file `bug' rather than  `a.out'.   In
general,  the history mechanisms may be used anywhere in the for-
mation of new commands and other characters may be placed  before
and after the substituted commands.

     We  then  ran the `size' command to see how large the binary
program images we have created were, and then an `ls -l'  command
with  the  same  argument  list,  denoting the argument list `*'.
Finally we ran the program `bug' to see that its output is indeed
correct.

     To  make  a numbered listing of the program we ran the `num'
command on the file `bug.c'.  In  order  to  compress  out  blank
lines in the output of `num' we ran the output through the filter
`ssp', but misspelled it as spp.  To correct this we used a shell
substitute, placing the old text and new text between `^' charac-
ters.  This is similar to the substitute command in  the  editor.
Finally,  we  repeated  the  same command with `!!', but sent its
output to the line printer.

     There are other mechanisms available for repeating commands.
The _h_i_s_t_o_r_y command prints out a number of previous commands with
numbers by which they can be referenced.  There is a way to refer
to a previous command by searching for a string which appeared in
it, and there are other, less useful, ways to select arguments to
include  in  a  new command.  A complete description of all these
mechanisms is given in the C shell manual pages in the UNIX  Pro-
grammer's Manual.









USD:4-20                           An Introduction to the C shell



     % cat bug.c
     main()

     {
          printf("hello);
     }
     % cc !$
     cc bug.c
     "bug.c", line 4: newline in string or char constant
     "bug.c", line 5: syntax error
     % ed !$
     ed bug.c
     29
     4s/);/"&/p
             printf("hello");
     w
     30
     q
     % !c
     cc bug.c
     % a.out
     hello% !e
     ed bug.c
     30
     4s/lo/lo\\n/p
             printf("hello\n");
     w
     32
     q
     % !c -o bug
     cc bug.c -o bug
     % size a.out bug
     a.out: 2784+364+1028 = 4176b = 0x1050b
     bug: 2784+364+1028 = 4176b = 0x1050b
     % ls -l !*
     ls -l a.out bug
     -rwxr-xr-x 1 bill       3932 Dec 19 09:41 a.out
     -rwxr-xr-x 1 bill       3932 Dec 19 09:42 bug
     % bug
     hello
     % num bug.c | spp
     spp: Command not found.
     % ^spp^ssp
     num bug.c | ssp
         1     main()
         3     {
         4          printf("hello\n");
         5     }
     % !! | lpr
     num bug.c | ssp | lpr
     %











An Introduction to the C shell                           USD:4-21


22..44..  AAlliiaasseess

     The  shell  has an _a_l_i_a_s mechanism which can be used to make
transformations on input commands.  This mechanism can be used to
simplify  the  commands  you type, to supply default arguments to
commands, or to perform transformations  on  commands  and  their
arguments.   The  alias  facility is similar to a macro facility.
Some of the features obtained by aliasing can  be  obtained  also
using  shell  command  files,  but  these  take  place in another
instance of the shell and  cannot  directly  affect  the  current
shells  environment  or involve commands such as _c_d which must be
done in the current shell.

     As an example, suppose that there is a new  version  of  the
mail  program  on  the  system  called `newmail' you wish to use,
rather than the standard mail program which is called `mail'.  If
you place the shell command

     alias mail newmail

in  your  _._c_s_h_r_c  file, the shell will transform an input line of
the form

     mail bill

into a call on `newmail'.  More generally, suppose  we  wish  the
command  `ls' to always show sizes of files, that is to always do
`-s'.  We can do

     alias ls ls -s

or even

     alias dir ls -s

creating a new command syntax `dir' which does an `ls -s'.  If we
say

     dir ~bill

then the shell will translate this to

     ls -s /mnt/bill


     Thus  the _a_l_i_a_s mechanism can be used to provide short names
for commands, to provide default arguments,  and  to  define  new
short  commands  in terms of other commands.  It is also possible
to define aliases which contain multiple commands  or  pipelines,
showing  where  the  arguments  to the original command are to be
substituted using the facilities of the history mechanism.   Thus
the definition











USD:4-22                           An Introduction to the C shell


     alias cd 'cd \!* ; ls '

would  do  an  _l_s command after each change directory _c_d command.
We enclosed the entire alias definition in `'' characters to pre-
vent most substitutions from occurring and the character `;' from
being recognized as a metacharacter.  The  `!'  here  is  escaped
with  a  `\'  to prevent it from being interpreted when the alias
command is typed in.  The `\!*' here substitutes the entire argu-
ment list to the pre-aliasing _c_d command, without giving an error
if there were no arguments.  The `;' separating commands is  used
here  to  indicate  that  one  command is to be done and then the
next.  Similarly the definition

     alias whois 'grep \!^ /etc/passwd'

defines a command which looks up its first argument in the  pass-
word file.

     WWaarrnniinngg:: The shell currently reads the _._c_s_h_r_c file each time
it starts up.  If you place a large  number  of  commands  there,
shells  will  tend  to  start slowly.  A mechanism for saving the
shell environment after  reading  the  _._c_s_h_r_c  file  and  quickly
restoring  it is under development, but for now you should try to
limit the number of aliases you have to a reasonable number... 10
or  15  is  reasonable, 50 or 60 will cause a noticeable delay in
starting up shells, and make the system seem  sluggish  when  you
execute commands from within the editor and other programs.

22..55..  MMoorree rreeddiirreeccttiioonn;; >>>> aanndd >>&&

     There  are  a few more notations useful to the terminal user
which have not been introduced yet.

     In addition to the standard output,  commands  also  have  a
_d_i_a_g_n_o_s_t_i_c _o_u_t_p_u_t which is normally directed to the terminal even
when the standard output is redirected to a file or a  pipe.   It
is  occasionally  desirable to direct the diagnostic output along
with the standard output.  For instance if you want  to  redirect
the output of a long running command into a file and wish to have
a record of any error diagnostic it produces you can do

     command >& file

The `>&' here tells the shell to route both the diagnostic output
and  the standard output into `file'.  Similarly you can give the
command

     command |& lpr

to route both standard and diagnostic output through the pipe  to
the line printer daemon _l_p_r_._[_+_+_]
-----------
[++] A command of the form
     command >&! file









An Introduction to the C shell                           USD:4-23


     Finally, it is possible to use the form

     command >> file

to place output at the end of an existing file.[+]

22..66..  JJoobbss;; BBaacckkggrroouunndd,, FFoorreeggrroouunndd,, oorr SSuussppeennddeedd

     When  one  or more commands are typed together as a pipeline
or as a sequence of commands separated by  semicolons,  a  single
_j_o_b is created by the shell consisting of these commands together
as a unit.  Single commands without pipes  or  semicolons  create
the  simplest  jobs.  Usually, every line typed to the shell cre-
ates a job.  Some lines that create jobs (one per line) are

     sort < data
     ls -s | sort -n | head -5
     mail harold


     If the metacharacter `&' is typed at the  end  of  the  com-
mands,  then  the job is started as a _b_a_c_k_g_r_o_u_n_d job.  This means
that the shell does not wait for it to complete  but  immediately
prompts  and  is  ready for another command.  The job runs _i_n _t_h_e
_b_a_c_k_g_r_o_u_n_d at the same time that normal jobs,  called  _f_o_r_e_g_r_o_u_n_d
jobs,  continue  to  be  read  and executed by the shell one at a
time.  Thus

     du > usage &

would run the _d_u program, which reports on the disk usage of your
working  directory (as well as any directories below it), put the
output into the file `usage' and return immediately with a prompt
for  the  next command without out waiting for _d_u to finish.  The
_d_u program would continue executing in the  background  until  it
finished,  even  though you can type and execute more commands in
the mean time.  When a background job terminates,  a  message  is
typed  by  the shell just before the next prompt telling you that
the job has completed.  In the following example the _d_u job  fin-
ishes  sometime  during the execution of the _m_a_i_l command and its
completion is reported just before the prompt after the _m_a_i_l  job
is finished.



-----------
exists,  and  is  used  when _n_o_c_l_o_b_b_e_r is set and _f_i_l_e
already exists.
[+] If _n_o_c_l_o_b_b_e_r is set, then an error will result  if
_f_i_l_e  does  not exist, otherwise the shell will create
_f_i_l_e if it doesn't exist.  A form
     command >>! file
makes it not be an error for file to  not  exist  when
_n_o_c_l_o_b_b_e_r is set.









USD:4-24                           An Introduction to the C shell


     % du > usage &
     [1] 503
     % mail bill
     How do you know when a background job is finished?
     EOT
     [1] - Done       du > usage
     %

If  the  job  did not terminate normally the `Done' message might
say something else like `Killed'.  If you want  the  terminations
of  background jobs to be reported at the time they occur (possi-
bly interrupting the output of other foreground  jobs),  you  can
set the _n_o_t_i_f_y variable.  In the previous example this would mean
that the `Done' message might have come right in  the  middle  of
the  message to Bill.  Background jobs are unaffected by any sig-
nals from the keyboard like the STOP, INTERRUPT, or QUIT  signals
mentioned earlier.

     Jobs  are  recorded  in  a table inside the shell until they
terminate.  In this table, the shell remembers the command names,
arguments  and  the _p_r_o_c_e_s_s _n_u_m_b_e_r_s of all commands in the job as
well as the working directory where the job  was  started.   Each
job  in  the  table  is either running _i_n _t_h_e _f_o_r_e_g_r_o_u_n_d with the
shell waiting for it to terminate, running _i_n _t_h_e _b_a_c_k_g_r_o_u_n_d_,  or
_s_u_s_p_e_n_d_e_d_.   Only one job can be running in the foreground at one
time, but several jobs can be suspended or running in  the  back-
ground  at  once.  As each job is started, it is assigned a small
identifying number called the _j_o_b _n_u_m_b_e_r which can be used  later
to refer to the job in the commands described below.  Job numbers
remain the same until the job terminates and then are re-used.

     When a job is started in the background using `&', its  num-
ber,  as  well as the process numbers of all its (top level) com-
mands, is typed by the shell before  prompting  you  for  another
command. For example,

     % ls -s | sort -n > usage &
     [2] 2034 2035
     %

runs  the  `ls'  program with the `-s' options, pipes this output
into the `sort' program with the `-n' option which puts its  out-
put  into  the file `usage'.  Since the `&' was at the end of the
line, these two programs were started together  as  a  background
job.   After starting the job, the shell prints the job number in
brackets (2 in this case) followed by the process number of  each
program  started  in  the job.  Then the shell immediates prompts
for a new command, leaving the job running simultaneously.

     As mentioned in section 1.8,  foreground  jobs  become  _s_u_s_-
_p_e_n_d_e_d  by  typing  ^Z which sends a STOP signal to the currently
running foreground job.  A background job can become suspended by
using  the _s_t_o_p command described below.  When jobs are suspended
they merely stop any further progress until started again, either









An Introduction to the C shell                           USD:4-25


in  the  foreground  or the background.  The shell notices when a
job becomes stopped and reports this fact, much like  it  reports
the  termination  of  background  jobs.  For foreground jobs this
looks like

     % du > usage
     ^Z
     Stopped
     %

`Stopped' message is typed by the shell when it notices that  the
_d_u program stopped.  For background jobs, using the _s_t_o_p command,
it is

     % sort usage &
     [1] 2345
     % stop %1
     [1] + Stopped (signal)sort usage
     %

Suspending foreground jobs can be very useful when  you  need  to
temporarily  change  what  you are doing (execute other commands)
and then return to the suspended job.  Also, foreground jobs  can
be  suspended  and then continued as background jobs using the _b_g
command, allowing you to continue other work and stop waiting for
the foreground job to finish.  Thus

     % du > usage
     ^Z
     Stopped
     % bg
     [1] du > usage &
     %

starts  `du' in the foreground, stops it before it finishes, then
continues it in the background allowing more foreground  commands
to be executed.  This is especially helpful when a foreground job
ends up taking longer than you expected  and  you  wish  you  had
started it in the background in the beginning.

     All  _j_o_b  _c_o_n_t_r_o_l commands can take an argument that identi-
fies a particular job.  All job name  arguments  begin  with  the
character `%', since some of the job control commands also accept
process numbers (printed by the _p_s  command.)   The  default  job
(when  no  argument  is  given)  is called the _c_u_r_r_e_n_t job and is
identified by a `+' in the output  of  the  _j_o_b_s  command,  which
shows  you  which jobs you have.  When only one job is stopped or
running in the background (the usual case) it is always the  cur-
rent  job  thus no argument is needed.  If a job is stopped while
running in the foreground it becomes  the  _c_u_r_r_e_n_t  job  and  the
existing  current  job becomes the _p_r_e_v_i_o_u_s job - identified by a
`-' in the output of _j_o_b_s_.  When the current job terminates,  the
previous  job  becomes the current job.  When given, the argument
is either `%-' (indicating the previous job); `%#',  where  #  is









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the  job  number; `%pref' where pref is some unique prefix of the
command name and arguments of one of the jobs; or  `%?'  followed
by some string found in only one of the jobs.

     The  _j_o_b_s  command  types  the table of jobs, giving the job
number, commands and status  (`Stopped'  or  `Running')  of  each
background  or  suspended  job.  With the `-l' option the process
numbers are also typed.

     % du > usage &
     [1] 3398
     % ls -s | sort -n > myfile &
     [2] 3405
     % mail bill
     ^Z
     Stopped
     % jobs
     [1] - Running    du > usage
     [2]    Running   ls -s | sort -n > myfile
     [3] + Stopped    mail bill
     % fg %ls
     ls -s | sort -n > myfile
     % more myfile


     The _f_g command runs a suspended or  background  job  in  the
foreground.   It is used to restart a previously suspended job or
change a background job to run in the foreground  (allowing  sig-
nals  or  input from the terminal).  In the above example we used
_f_g to change the `ls' job from the background to  the  foreground
since  we  wanted  to wait for it to finish before looking at its
output file.  The _b_g command runs a suspended job  in  the  back-
ground.   It is usually used after stopping the currently running
foreground job with the STOP signal.  The combination of the STOP
signal  and  the _b_g command changes a foreground job into a back-
ground job.  The _s_t_o_p command suspends a background job.

     The _k_i_l_l command terminates a background  or  suspended  job
immediately.   In  addition to jobs, it may be given process num-
bers as arguments, as printed by _p_s_.  Thus, in the example above,
the running _d_u command could have been terminated by the command

     % kill %1
     [1]  Terminated  du > usage
     %


     The  _n_o_t_i_f_y  command  (not  the  variable mentioned earlier)
indicates that the  termination  of  a  specific  job  should  be
reported  at the time it finishes instead of waiting for the next
prompt.

     If a job running in the background tries to read input  from
the  terminal  it  is  automatically stopped.  When such a job is









An Introduction to the C shell                           USD:4-27


then run in the foreground, input can be given to  the  job.   If
desired,  the  job  can  be  run in the background again until it
requests input again.   This  is  illustrated  in  the  following
sequence  where  the  `s' command in the text editor might take a
long time.

     % ed bigfile
     120000
     1,$s/thisword/thatword/
     ^Z
     Stopped
     % bg
     [1] ed bigfile &
     %
      . . .  some foreground commands
     [1] Stopped (tty input)ed bigfile
     % fg
     ed bigfile
     w
     120000
     q
     %

So after the `s' command was issued, the  `ed'  job  was  stopped
with ^Z and then put in the background using _b_g_.  Some time later
when the `s' command was finished, _e_d tried to read another  com-
mand  and  was stopped because jobs in the background cannot read
from the terminal.  The _f_g command returned the `ed' job  to  the
foreground  where  it  could  once again accept commands from the
terminal.

     The command

     stty tostop

causes all background jobs run on your terminal to stop when they
are  about  to  write output to the terminal.  This prevents mes-
sages from background jobs from interrupting foreground job  out-
put  and allows you to run a job in the background without losing
terminal output.  It also can be used  for  interactive  programs
that  sometimes have long periods without interaction.  Thus each
time it outputs a prompt for more input it will stop  before  the
prompt.   It  can  then  be  run in the foreground using _f_g_, more
input can be given and, if necessary stopped and returned to  the
background.   This  _s_t_t_y  command might be a good thing to put in
your _._l_o_g_i_n file if you do not like output from  background  jobs
interrupting  your  work.   It also can reduce the need for redi-
recting the output of background jobs if the output is  not  very
big:














USD:4-28                           An Introduction to the C shell


     % stty tostop
     % wc hugefile &
     [1] 10387
     % ed text
     . . . some time later
     q
     [1] Stopped (tty output)wc hugefile
     % fg wc
     wc hugefile
        13371   30123   302577
     % stty -tostop

Thus  after  some  time the `wc' command, which counts the lines,
words and characters in a file, had one line of output.  When  it
tried to write this to the terminal it stopped.  By restarting it
in the foreground we allowed it to write on the terminal  exactly
when we were ready to look at its output.  Programs which attempt
to change the mode of the terminal will also  block,  whether  or
not  _t_o_s_t_o_p  is  set,  when they are not in the foreground, as it
would be very unpleasant to have  a  background  job  change  the
state of the terminal.

     Since  the _j_o_b_s command only prints jobs started in the cur-
rently executing shell, it knows nothing  about  background  jobs
started  in  other  login sessions or within shell files.  The _p_s
can be used in this case to find out about  background  jobs  not
started in the current shell.

22..77..  WWoorrkkiinngg DDiirreeccttoorriieess

     As  mentioned  in section 1.6, the shell is always in a par-
ticular _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y_.  The `change directory' command  _c_h_d_i_r
(its  short  form _c_d may also be used) changes the working direc-
tory of the shell, that is, changes the directory you are located
in.

     It  is  useful to make a directory for each project you wish
to work on and to place all files related to that project in that
directory.   The  `make  directory' command, _m_k_d_i_r_, creates a new
directory.  The _p_w_d (`print working directory')  command  reports
the absolute pathname of the working directory of the shell, that
is, the directory you are located in.  Thus in the example below:

     % pwd
     /usr/bill
     % mkdir newpaper
     % chdir newpaper
     % pwd
     /usr/bill/newpaper
     %

the user has created and moved to the directory _n_e_w_p_a_p_e_r_.  where,
for example, he might place a group of related files.










An Introduction to the C shell                           USD:4-29


     No matter where you have moved to in a directory  hierarchy,
you can return to your `home' login directory by doing just

     cd

with  no  arguments.   The  name  `..' always means the directory
above the current one in the hierarchy, thus

     cd ..

changes the shell's working directory to the one  directly  above
the  current  one.   The  name  `..' can be used in any pathname,
thus,

     cd ../programs

means change to the directory `programs' contained in the  direc-
tory  above the current one.  If you have several directories for
different projects under, say, your home directory,  this  short-
hand notation permits you to switch easily between them.

     The shell always remembers the pathname of its current work-
ing directory in  the  variable  _c_w_d_.   The  shell  can  also  be
requested to remember the previous directory when you change to a
new working directory.  If the `push directory' command _p_u_s_h_d  is
used  in place of the _c_d command, the shell saves the name of the
current working directory on a _d_i_r_e_c_t_o_r_y _s_t_a_c_k before changing to
the  new  one.   You  can see this list at any time by typing the
`directories' command _d_i_r_s_.

     % pushd newpaper/references
     ~/newpaper/references  ~
     % pushd /usr/lib/tmac
     /usr/lib/tmac  ~/newpaper/references  ~
     % dirs
     /usr/lib/tmac  ~/newpaper/references  ~
     % popd
     ~/newpaper/references  ~
     % popd
     ~
     %

The list is printed in a horizontal line, reading left to  right,
with  a  tilde  (~) as shorthand for your home directory--in this
case `/usr/bill'.  The directory stack is printed whenever  there
is  more than one entry on it and it changes.  It is also printed
by a _d_i_r_s command.  _D_i_r_s is usually faster and  more  informative
than  _p_w_d since it shows the current working directory as well as
any other directories remembered in the stack.

     The _p_u_s_h_d command with no argument  alternates  the  current
directory  with the first directory in the list.  The `pop direc-
tory' _p_o_p_d command without an argument returns you to the  direc-
tory  you  were  in  prior  to  the  current  one, discarding the









USD:4-30                           An Introduction to the C shell


previous current directory from the stack (forgetting it).   Typ-
ing _p_o_p_d several times in a series takes you backward through the
directories you had been in (changed to) by _p_u_s_h_d command.  There
are other options to _p_u_s_h_d and _p_o_p_d to manipulate the contents of
the directory stack and to change to directories not at  the  top
of the stack; see the _c_s_h manual page for details.

     Since  the  shell  remembers  the working directory in which
each job was started, it warns you when you might be confused  by
restarting  a job in the foreground which has a different working
directory than the current working directory of the shell.   Thus
if  you  start  a background job, then change the shell's working
directory and then cause the background job to run in  the  fore-
ground,  the  shell  warns  you that the working directory of the
currently running foreground job is different from  that  of  the
shell.

     % dirs -l
     /mnt/bill
     % cd myproject
     % dirs
     ~/myproject
     % ed prog.c
     1143
     ^Z
     Stopped
     % cd ..
     % ls
     myproject
     textfile
     % fg
     ed prog.c (wd: ~/myproject)

This  way  the shell warns you when there is an implied change of
working directory, even though no cd command was issued.  In  the
above  example the `ed' job was still in `/mnt/bill/project' even
though the shell had changed to `/mnt/bill'.  A  similar  warning
is  given  when  such a foreground job terminates or is suspended
(using the STOP signal) since  the  return  to  the  shell  again
implies a change of working directory.

     % fg
     ed prog.c (wd: ~/myproject)
      . . . after some editing
     q
     (wd now: ~)
     %

These  messages  are sometimes confusing if you use programs that
change their own working directories, since the shell only remem-
bers  which  directory  a job is started in, and assumes it stays
there.  The `-l' option of _j_o_b_s will type the  working  directory
of  suspended  or  background  jobs when it is different from the
current working directory of the shell.









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22..88..  UUsseeffuull bbuuiilltt--iinn ccoommmmaannddss

     We now give a few of the useful  built-in  commands  of  the
shell describing how they are used.

     The  _a_l_i_a_s  command  described  above  is used to assign new
aliases and to show the existing aliases.  With no  arguments  it
prints  the current aliases.  It may also be given only one argu-
ment such as

     alias ls

to show the current alias for, e.g., `ls'.

     The _e_c_h_o command prints its arguments.  It is often used  in
_s_h_e_l_l  _s_c_r_i_p_t_s  or as an interactive command to see what filename
expansions will produce.

     The _h_i_s_t_o_r_y command will show the contents  of  the  history
list.   The  numbers given with the history events can be used to
reference previous events which are difficult to reference  using
the  contextual  mechanisms  introduced  above.   There is also a
shell variable called _p_r_o_m_p_t_.  By placing a `!' character in  its
value  the  shell will there substitute the number of the current
command in the history list.  You can use this number to refer to
this command in a history substitution.  Thus you could

     set prompt='\! % '

Note  that  the  `!' character had to be _e_s_c_a_p_e_d here even within
`'' characters.

     The _l_i_m_i_t command is used  to  restrict  use  of  resources.
With no arguments it prints the current limitations:

     cputime   unlimited
     filesize  unlimited
     datasize  5616 kbytes
     stacksize 512 kbytes
     coredumpsizeunlimited

Limits can be set, e.g.:

     limit coredumpsize 128k

Most reasonable units abbreviations will work; see the _c_s_h manual
page for more details.

     The _l_o_g_o_u_t command can be used to terminate  a  login  shell
which has _i_g_n_o_r_e_e_o_f set.

     The  _r_e_h_a_s_h command causes the shell to recompute a table of
where commands are located.  This is necessary if you add a  com-
mand  to  a directory in the current shell's search path and wish









USD:4-32                           An Introduction to the C shell


the shell to find it, since otherwise the hashing  algorithm  may
tell the shell that the command wasn't in that directory when the
hash table was computed.

     The _r_e_p_e_a_t command can be used to repeat a  command  several
times.   Thus  to  make 5 copies of the file _o_n_e in the file _f_i_v_e
you could do

     repeat 5 cat one >> five


     The _s_e_t_e_n_v command can be used to set variables in the envi-
ronment.  Thus

     setenv TERM adm3a

will  set  the value of the environment variable TERM to `adm3a'.
A user program _p_r_i_n_t_e_n_v exists which will print out the  environ-
ment.  It might then show:

     % printenv
     HOME=/usr/bill
     SHELL=/bin/csh
     PATH=:/usr/ucb:/bin:/usr/bin:/usr/local
     TERM=adm3a
     USER=bill
     %


     The _s_o_u_r_c_e command can be used to force the current shell to
read commands from a file.  Thus

     source .cshrc

can be used after editing in a change to the  _._c_s_h_r_c  file  which
you wish to take effect right away.

     The  _t_i_m_e command can be used to cause a command to be timed
no matter how much CPU time it takes.  Thus

     % time cp /etc/rc /usr/bill/rc
     0.0u 0.1s 0:01 8% 2+1k 3+2io 1pf+0w
     % time wc /etc/rc /usr/bill/rc
          52    178   1347 /etc/rc
          52    178   1347 /usr/bill/rc
         104    356   2694 total
     0.1u 0.1s 0:00 13% 3+3k 5+3io 7pf+0w
     %

indicates that the _c_p command used a negligible  amount  of  user
time  (u) and about 1/10th of a system time (s); the elapsed time
was 1 second (0:01), there was an  average  memory  usage  of  2k
bytes  of  program  space and 1k bytes of data space over the cpu
time involved (2+1k); the program did three disk  reads  and  two









An Introduction to the C shell                           USD:4-33


disk  writes (3+2io), and took one page fault and was not swapped
(1pf+0w).  The word count command _w_c on the other hand  used  0.1
seconds  of user time and 0.1 seconds of system time in less than
a second of elapsed time.  The percentage  `13%'  indicates  that
over the period when it was active the command `wc' used an aver-
age of 13 percent of the available CPU cycles of the machine.

     The _u_n_a_l_i_a_s and _u_n_s_e_t commands can be used to remove aliases
and  variable  definitions  from  the shell, and _u_n_s_e_t_e_n_v removes
variables from the environment.

22..99..  WWhhaatt eellssee??

     This concludes the basic discussion of the shell for  termi-
nal  users.  There are more features of the shell to be discussed
here, and all features of the shell are discussed in  its  manual
pages.   One useful feature which is discussed later is the _f_o_r_e_-
_a_c_h built-in command which can be used to run  the  same  command
sequence with a number of different arguments.

     If  you intend to use UNIX a lot you you should look through
the rest of this document and the csh manual pages (section1)  to
become  familiar with the other facilities which are available to
you.







































USD:4-34                           An Introduction to the C shell


33..  SShheellll ccoonnttrrooll ssttrruuccttuurreess aanndd ccoommmmaanndd ssccrriippttss

33..11..  IInnttrroodduuccttiioonn

     It is possible to place  commands  in  files  and  to  cause
shells  to  be  invoked  to  read and execute commands from these
files, which are called _s_h_e_l_l _s_c_r_i_p_t_s_.  We here detail those fea-
tures of the shell useful to the writers of such scripts.

33..22..  MMaakkee

     It  is  important  to  first note what shell scripts are _n_o_t
useful for.  There is a program called _m_a_k_e which is very  useful
for  maintaining  a  group of related files or performing sets of
operations on related files.  For instance a large  program  con-
sisting  of one or more files can have its dependencies described
in a _m_a_k_e_f_i_l_e which contains definitions of the commands used  to
create  these different files when changes occur.  Definitions of
the means for printing listings, cleaning  up  the  directory  in
which the files reside, and installing the resultant programs are
easily, and most appropriately placed  in  this  _m_a_k_e_f_i_l_e_.   This
format is superior and preferable to maintaining a group of shell
procedures to maintain these files.

     Similarly when working on a document a _m_a_k_e_f_i_l_e may be  cre-
ated  which defines how different versions of the document are to
be created and which options of _n_r_o_f_f or _t_r_o_f_f are appropriate.

33..33..  IInnvvooccaattiioonn aanndd tthhee aarrggvv vvaarriiaabbllee

     A _c_s_h command script may be interpreted by saying

     % csh script ...

where _s_c_r_i_p_t is the name of the file containing a  group  of  _c_s_h
commands  and  `...' is replaced by a sequence of arguments.  The
shell places these arguments in the variable _a_r_g_v and then begins
to  read  commands  from  the  script.  These parameters are then
available through the same mechanisms which are used to reference
any other shell variables.

     If you make the file `script' executable by doing

     chmod 755 script

and  place  a  shell comment at the beginning of the shell script
(i.e. begin the file with a `#' character) then a `/bin/csh' will
automatically be invoked to execute `script' when you type

     script

If  the  file  does  not begin with a `#' then the standard shell
`/bin/sh' will be used to execute it.  This allows you to convert
your older shell scripts to use _c_s_h at your convenience.









An Introduction to the C shell                           USD:4-35


33..44..  VVaarriiaabbllee ssuubbssttiittuuttiioonn

     After  each input line is broken into words and history sub-
stitutions are done on it, the input line is parsed into distinct
commands.   Before  each  command is executed a mechanism know as
_v_a_r_i_a_b_l_e _s_u_b_s_t_i_t_u_t_i_o_n is done on these words.  Keyed by the char-
acter  `$'  this  substitution replaces the names of variables by
their values.  Thus

     echo $argv

when placed in a command script would cause the current value  of
the variable _a_r_g_v to be echoed to the output of the shell script.
It is an error for _a_r_g_v to be unset at this point.

     A number of notations are provided for accessing  components
and attributes of variables.  The notation

     $?name

expands  to  `1' if name is _s_e_t or to `0' if name is not _s_e_t_.  It
is the fundamental mechanism used for checking whether particular
variables  have  been assigned values.  All other forms of refer-
ence to undefined variables cause errors.

     The notation

     $#name

expands to the number of elements in the variable _n_a_m_e_.  Thus

     % set argv=(a b c)
     % echo $?argv
     1
     % echo $#argv
     3
     % unset argv
     % echo $?argv
     0
     % echo $argv
     Undefined variable: argv.
     %


     It is also possible to access the components of  a  variable
which has several values.  Thus

     $argv[1]

gives  the  first  component of _a_r_g_v or in the example above `a'.
Similarly

     $argv[$#argv]










USD:4-36                           An Introduction to the C shell


would give `c', and

     $argv[1-2]

would give `a b'. Other notations useful in shell scripts are

     $_n

where _n is an integer as a shorthand for

     $argv[_n]

the _n_t_h parameter and

     $*

which is a shorthand for

     $argv

The form

     $$

expands to the process number of the current shell.   Since  this
process  number is unique in the system it can be used in genera-
tion of unique temporary file names.  The form

     $<

is quite special and is replaced by the next line of  input  read
from  the  shell's standard input (not the script it is reading).
This is useful for writing shell scripts  that  are  interactive,
reading  commands  from  the  terminal,  or  even writing a shell
script that acts as a filter, reading lines from its input  file.
Thus the sequence

     echo 'yes or no?\c'
     set a=($<)

would  write  out  the  prompt `yes or no?' without a newline and
then read the answer into the variable `a'.  In this  case  `$#a'
would  be  `0'  if  either  a  blank line or end-of-file (^D) was
typed.

     One minor difference between `$_n' and `$argv[_n]'  should  be
noted  here.  The form `$argv[_n]' will yield an error if _n is not
in the range `1-$#argv' while `$n' will never  yield  an  out  of
range  subscript  error.   This is for compatibility with the way
older shells handled parameters.

     Another important point is that it is never an error to give
a  subrange of the form `n-'; if there are less than _n components
of the given variable then no words are substituted.  A range  of









An Introduction to the C shell                           USD:4-37


the form `m-n' likewise returns an empty vector without giving an
error when _m exceeds the number of elements of  the  given  vari-
able, provided the subscript _n is in range.

33..55..  EExxpprreessssiioonnss

     In  order for interesting shell scripts to be constructed it
must be possible to evaluate expressions in the  shell  based  on
the  values of variables.  In fact, all the arithmetic operations
of the language C are available in the shell with the same prece-
dence  that  they  have in C.  In particular, the operations `=='
and `!=' compare strings and the operators `&&' and  `||'  imple-
ment  the  boolean and/or operations.  The special operators `=~'
and `!~' are similar to `==' and `!=' except that the  string  on
the right side can have pattern matching characters (like *, ? or
[]) and the test is whether the string on the  left  matches  the
pattern on the right.

     The shell also allows file enquiries of the form

     -? filename

where  `?'  is  replace  by  a  number of single characters.  For
instance the expression primitive

     -e filename

tell whether the file `filename' exists.  Other  primitives  test
for  read,  write and execute access to the file, whether it is a
directory, or has non-zero length.

     It is possible to test whether  a  command  terminates  nor-
mally,  by  a  primitive  of the form `{ command }' which returns
true, i.e. `1' if the command succeeds exiting normally with exit
status  0,  or  `0'  if the command terminates abnormally or with
exit status non-zero.  If more  detailed  information  about  the
execution status of a command is required, it can be executed and
the variable `$status'  examined  in  the  next  command.   Since
`$status'  is set by every command, it is very transient.  It can
be saved if it is inconvenient to use it only in the single imme-
diately following command.

     For  a  full list of expression components available see the
manual section for the shell.

33..66..  SSaammppllee sshheellll ssccrriipptt

     A sample shell script which  makes  use  of  the  expression
mechanism of the shell and some of its control structure follows:














USD:4-38                           An Introduction to the C shell


     % cat copyc
     #
     # Copyc copies those C programs in the specified list
     # to the directory ~/backup if they differ from the files
     # already in ~/backup
     #
     set noglob
     foreach i ($argv)

             if ($i !~ *.c) continue  # not a .c file so do nothing

             if (! -r ~/backup/$i:t) then
                     echo $i:t not in backup... not cp\'ed
                     continue
             endif

             cmp -s $i ~/backup/$i:t # to set $status

             if ($status != 0) then
                     echo new backup of $i
                     cp $i ~/backup/$i:t
             endif
     end


     This script makes use of the _f_o_r_e_a_c_h command,  which  causes
the  shell  to  execute  the commands between the _f_o_r_e_a_c_h and the
matching _e_n_d for each of the values given  between  `('  and  `)'
with  the named variable, in this case `i' set to successive val-
ues in the list.  Within this loop we may use the  command  _b_r_e_a_k
to  stop executing the loop and _c_o_n_t_i_n_u_e to prematurely terminate
one iteration and begin the next.  After  the  _f_o_r_e_a_c_h  loop  the
iteration  variable  (_i  in  this case) has the value at the last
iteration.

     We set the variable _n_o_g_l_o_b here to prevent  filename  expan-
sion of the members of _a_r_g_v_.  This is a good idea, in general, if
the arguments to a shell script are filenames which have  already
been  expanded or if the arguments may contain filename expansion
metacharacters.  It is also possible to quote each use of  a  `$'
variable expansion, but this is harder and less reliable.

     The  other control construct used here is a statement of the
form

     iiff ( expression ) tthheenn
          command
          ...
     eennddiiff

The placement of the keywords here is nnoott  flexible  due  to  the
current implementation of the shell.[+]
-----------
[+]The following two formats are not currently accept-









An Introduction to the C shell                           USD:4-39


     The shell does have another form of the if statement of  the
form

     iiff ( expression ) ccoommmmaanndd

which can be written

     iiff ( expression ) \
          command

Here we have escaped the newline for the sake of appearance.  The
command must not involve `|', `&' or `;' and must not be  another
control command.  The second form requires the final `\' to iimmmmee--
ddiiaatteellyy precede the end-of-line.

     The more general _i_f statements above also admit  a  sequence
of _e_l_s_e_-_i_f pairs followed by a single _e_l_s_e and an _e_n_d_i_f_, e.g.:

     iiff ( expression ) tthheenn
          commands
     eellssee iiff (expression ) tthheenn
          commands
     ...

     eellssee
          commands
     eennddiiff


     Another important mechanism used in shell scripts is the `:'
modifier.  We can use the modifier `:r' here to extract a root of
a  filename  or `:e' to extract the _e_x_t_e_n_s_i_o_n_.  Thus if the vari-
able _i has the value `/mnt/foo.bar' then

     % echo $i $i:r $i:e
     /mnt/foo.bar /mnt/foo bar
     %

shows how the `:r' modifier strips off the  trailing  `.bar'  and
the  the  `:e'  modifier  leaves only the `bar'.  Other modifiers
will take off the last component of a pathname leaving  the  head
`:h' or all but the last component of a pathname leaving the tail
-----------
able to the shell:

     iiff ( expression )        # WWoonn''tt wwoorrkk!!
     tthheenn
          command
          ...
     eennddiiff

and

     iiff ( expression ) tthheenn command eennddiiff         # WWoonn''tt wwoorrkk









USD:4-40                           An Introduction to the C shell


`:t'.  These modifiers are fully  described  in  the  _c_s_h  manual
pages in the User's Reference Manual.  It is also possible to use
the _c_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n mechanism described in  the  next  major
section  to  perform modifications on strings to then reenter the
shell's environment.  Since each usage of this mechanism involves
the  creation  of a new process, it is much more expensive to use
than the `:' modification mechanism.[++] Finally,  we  note  that
the  character  `#' lexically introduces a shell comment in shell
scripts (but not from the terminal).  All  subsequent  characters
on  the  input line after a `#' are discarded by the shell.  This
character can be quoted using `'' or `\' to place it in an  argu-
ment word.

33..77..  OOtthheerr ccoonnttrrooll ssttrruuccttuurreess

     The shell also has control structures _w_h_i_l_e and _s_w_i_t_c_h simi-
lar to those of C.  These take the forms

     wwhhiillee ( expression )
          commands
     eenndd

and

     sswwiittcchh ( word )

     ccaassee str1:
          commands
          bbrreeaakkssww

      ...

     ccaassee strn:
          commands
          bbrreeaakkssww

     ddeeffaauulltt::
          commands
          bbrreeaakkssww

     eennddssww

For details see the manual section for _c_s_h_.  C programmers should
note  that we use _b_r_e_a_k_s_w to exit from a _s_w_i_t_c_h while _b_r_e_a_k exits
-----------
[++] It is also important to  note  that  the  current
implementation  of  the shell limits the number of `:'
modifiers on a `$' substitution to 1.  Thus

     % echo $i $i:h:t
     /a/b/c /a/b:t
     %

does not do what one would expect.









An Introduction to the C shell                           USD:4-41


a _w_h_i_l_e or _f_o_r_e_a_c_h loop.  A common mistake to make in _c_s_h scripts
is to use _b_r_e_a_k rather than _b_r_e_a_k_s_w in switches.

     Finally,  _c_s_h  allows  a _g_o_t_o statement, with labels looking
like they do in C, i.e.:

     loop:
          commands
          ggoottoo loop


33..88..  SSuuppppllyyiinngg iinnppuutt ttoo ccoommmmaannddss

     Commands run from shell scripts receive by default the stan-
dard  input  of  the  shell which is running the script.  This is
different from previous shells running  under  UNIX.   It  allows
shell  scripts  to  fully  participate in pipelines, but mandates
extra notation for commands which are to take inline data.

     Thus we need a metanotation for  supplying  inline  data  to
commands  in  shell scripts.  As an example, consider this script
which runs the editor to delete leading blanks from the lines  in
each argument file:

     % cat deblank
     # deblank -- remove leading blanks
     foreach i ($argv)
     ed - $i << 'EOF'
     1,$s/^[ ]*//
     w
     q
     'EOF'
     end
     %

The  notation `<< 'EOF'' means that the standard input for the _e_d
command is to come from the text in the shell script file  up  to
the  next  line consisting of exactly `'EOF''.  The fact that the
`EOF' is enclosed in `''  characters,  i.e.  quoted,  causes  the
shell  to  not  perform  variable substitution on the intervening
lines.  In general, if any part of the word  following  the  `<<'
which  the  shell  uses  to terminate the text to be given to the
command is quoted then these substitutions will not be performed.
In this case since we used the form `1,$' in our editor script we
needed to insure that this `$' was not variable substituted.   We
could  also  have  insured  this by preceding the `$' here with a
`\', i.e.:

     1,\$s/^[ ]*//

but quoting the `EOF'  terminator  is  a  more  reliable  way  of
achieving the same thing.











USD:4-42                           An Introduction to the C shell


33..99..  CCaattcchhiinngg iinntteerrrruuppttss

     If  our shell script creates temporary files, we may wish to
catch interruptions of the shell script so that we can  clean  up
these files.  We can then do

     onintr label

where  _l_a_b_e_l  is  a  label  in  our  program.  If an interrupt is
received the shell will do a `goto label' and we can  remove  the
temporary files and then do an _e_x_i_t command (which is built in to
the shell) to exit from the shell script.  If  we  wish  to  exit
with a non-zero status we can do

     exit(1)

e.g. to exit with status `1'.

33..1100..  WWhhaatt eellssee??

     There  are  other features of the shell useful to writers of
shell procedures.  The _v_e_r_b_o_s_e and _e_c_h_o options and  the  related
_-_v  and  _-_x  command  line  options can be used to help trace the
actions of the shell.  The _-_n option causes  the  shell  only  to
read  commands  and  not  to execute them and may sometimes be of
use.

     One other thing to note is that _c_s_h will not  execute  shell
scripts  which do not begin with the character `#', that is shell
scripts that  do  not  begin  with  a  comment.   Similarly,  the
`/bin/sh'  on  your  system  may well defer to `csh' to interpret
shell scripts which begin with `#'.  This  allows  shell  scripts
for both shells to live in harmony.

     There  is  also  another quotation mechanism using `"' which
allows only some of the expansion mechanisms we have so far  dis-
cussed  to  occur  on  the  quoted string and serves to make this
string into a single word as `'' does.

























An Introduction to the C shell                           USD:4-43


44..  OOtthheerr,, lleessss ccoommmmoonnllyy uusseedd,, sshheellll ffeeaattuurreess

44..11..  LLooooppss aatt tthhee tteerrmmiinnaall;; vvaarriiaabblleess aass vveeccttoorrss

     It is occasionally useful to use the _f_o_r_e_a_c_h control  struc-
ture  at  the  terminal  to aid in performing a number of similar
commands.  For instance, there were at one point three shells  in
use  on the Cory UNIX system at Cory Hall, `/bin/sh', `/bin/nsh',
and `/bin/csh'.  To count the number of persons using each  shell
one could have issued the commands

     % grep -c csh$ /etc/passwd
     27
     % grep -c nsh$ /etc/passwd
     128
     % grep -c -v sh$ /etc/passwd
     430
     %

Since  these  commands  are very similar we can use _f_o_r_e_a_c_h to do
this more easily.

     % foreach i ('sh$' 'csh$' '-v sh$')
     ? grep -c $i /etc/passwd
     ? end
     27
     128
     430
     %

Note here that the shell prompts for input with `? ' when reading
the body of the loop.

     Very  useful with loops are variables which contain lists of
filenames or other words.  You can, for example, do

     % set a=(`ls`)
     % echo $a
     csh.n csh.rm
     % ls
     csh.n
     csh.rm
     % echo $#a
     2
     %

The _s_e_t command here gave the variable _a a list of all the  file-
names  in  the  current  directory as value.  We can then iterate
over these names to perform any chosen function.

     The output of a command within ``' characters  is  converted
by  the  shell  to  a  list of words.  You can also place the ``'
quoted string within `"' characters to take each (non-empty) line
as  a  component of the variable; preventing the lines from being









USD:4-44                           An Introduction to the C shell


split into words at blanks and  tabs.   A  modifier  `:x'  exists
which  can be used later to expand each component of the variable
into another variable splitting it into separate words at  embed-
ded blanks and tabs.

44..22..  BBrraacceess {{ ...... }} iinn aarrgguummeenntt eexxppaannssiioonn

     Another  form  of  filename  expansion,  alluded  to  before
involves the characters `{' and `}'.   These  characters  specify
that  the  contained strings, separated by `,' are to be consecu-
tively substituted into the containing characters and the results
expanded left to right.  Thus

     A{str1,str2,...strn}B

expands to

     Astr1B Astr2B ... AstrnB

This  expansion  occurs before the other filename expansions, and
may be applied recursively (i.e. nested).  The  results  of  each
expanded  string are sorted separately, left to right order being
preserved.  The resulting filenames are not required to exist  if
no  other  expansion  mechanisms  are used.  This means that this
mechanism can be used to generate arguments which are  not  file-
names, but which have common parts.

     A typical use of this would be

     mkdir ~/{hdrs,retrofit,csh}

to  make subdirectories `hdrs', `retrofit' and `csh' in your home
directory.  This mechanism is most useful when the common  prefix
is longer than in this example, i.e.

     chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}


44..33..  CCoommmmaanndd ssuubbssttiittuuttiioonn

     A  command  enclosed  in  ``'  characters  is replaced, just
before filenames are expanded, by the output from  that  command.
Thus it is possible to do

     set pwd=`pwd`

to save the current directory in the variable _p_w_d or to do

     ex `grep -l TRACE *.c`

to  run  the  editor  _e_x supplying as arguments those files whose
names end in `.c' which have the string `TRACE' in them.*
-----------
*Command expansion also  occurs  in  input  redirected









An Introduction to the C shell                           USD:4-45


44..44..  OOtthheerr ddeettaaiillss nnoott ccoovveerreedd hheerree

     In particular circumstances it may be necessary to know  the
exact  nature  and  order of different substitutions performed by
the shell.  The exact meaning of certain combinations  of  quota-
tions  is  also occasionally important.  These are detailed fully
in its manual section.

     The shell has a number of command line option  flags  mostly
of  use  in  writing  UNIX programs, and debugging shell scripts.
See the csh(1) manual section for a list of these options.








































-----------
with  `<<'  and  within  `"' quotations.  Refer to the
shell manual section for full details.









USD:4-46                           An Introduction to the C shell


AAppppeennddiixx -- SSppeecciiaall cchhaarraacctteerrss

The following table lists the special characters of _c_s_h  and  the
UNIX  system,  giving for each the section(s) in which it is dis-
cussed.  A number of these characters also have  special  meaning
in  expressions.  See the _c_s_h manual section for a complete list.

Syntactic metacharacters

     ;    2.4  separates commands to be executed sequentially
     |    1.5  separates commands in a pipeline
     ( )  2.2,3.6   brackets expressions and variable values
     &    2.5  follows commands to be executed without waiting for completion


Filename metacharacters

     /    1.6  separates components of a file's pathname
     .    1.6  separates root parts of a file name from extensions
     ?    1.6  expansion character matching any single character
     *    1.6  expansion character matching any sequence of characters
     [ ]  1.6  expansion sequence matching any single character from a set
     ~    1.6  used at the beginning of a filename to indicate home directories
     { }  4.2  used to specify groups of arguments with common parts


Quotation metacharacters

     \    1.7  prevents meta-meaning of following single character
     '    1.7  prevents meta-meaning of a group of characters
     "    4.3  like ', but allows variable and command expansion


Input/output metacharacters

     <    1.5  indicates redirected input
     >    1.3  indicates redirected output


Expansion/substitution metacharacters

     $    3.4  indicates variable substitution
     !    2.3  indicates history substitution
     :    3.6  precedes substitution modifiers
     ^    2.3  used in special forms of history substitution
     `    4.3  indicates command substitution


Other metacharacters

     #    1.3,3.6   begins scratch file names; indicates shell comments
     -    1.2  prefixes option (flag) arguments to commands
     %    2.6  prefixes job name specifications










An Introduction to the C shell                           USD:4-47


GGlloossssaarryy

     This glossary lists the most important terms  introduced  in
the introduction to the shell and gives references to sections of
the shell document for further information  about  them.   Refer-
ences of the form `pr (1)' indicate that the command _p_r is in the
UNIX User Reference manual in section 1.   You  can  look  at  an
online copy of its manual page by doing

     man 1 pr

References  of  the form (2.5) indicate that more information can
be found in section 2.5 of this manual.

..              Your current directory has the name `.' as well as
               the  name  printed  by  the  command _p_w_d_; see also
               _d_i_r_s_.  The current directory `.'  is  usually  the
               first  _c_o_m_p_o_n_e_n_t  of  the search path contained in
               the variable _p_a_t_h, thus commands which are in  `.'
               are  found first (2.2).  The character `.' is also
               used in separating _c_o_m_p_o_n_e_n_t_s of filenames  (1.6).
               The  character `.' at the beginning of a _c_o_m_p_o_n_e_n_t
               of a _p_a_t_h_n_a_m_e is treated specially and not matched
               by the _f_i_l_e_n_a_m_e _e_x_p_a_n_s_i_o_n metacharacters `?', `*',
               and `[' `]' pairs (1.6).

....             Each directory has a file `..' in it  which  is  a
               reference to its parent directory.  After changing
               into the directory with _c_h_d_i_r, i.e.

                    chdir paper

               you can return to the parent directory by doing

                    chdir ..

               The current directory is printed by _p_w_d (2.7).

a.out          Compilers which create  executable  images  create
               them, by default, in the file _a_._o_u_t_.  for histori-
               cal reasons (2.3).

absolute pathname
               A _p_a_t_h_n_a_m_e which begins with  a  `/'  is  _a_b_s_o_l_u_t_e
               since  it  specifies  the _p_a_t_h of directories from
               the beginning of the  entire  directory  system  -
               called  the  _r_o_o_t  directory.  _P_a_t_h_n_a_m_es which are
               not _a_b_s_o_l_u_t_e are called _r_e_l_a_t_i_v_e  (see  definition
               of _r_e_l_a_t_i_v_e _p_a_t_h_n_a_m_e) (1.6).

alias          An _a_l_i_a_s specifies a shorter or different name for
               a UNIX command, or a transformation on  a  command
               to  be  performed  in  the shell.  The shell has a
               command _a_l_i_a_s which establishes  _a_l_i_a_s_e_s  and  can









USD:4-48                           An Introduction to the C shell


               print  their  current values.  The command _u_n_a_l_i_a_s
               is used to remove _a_l_i_a_s_e_s (2.4).

argument       Commands in UNIX receive a list of _a_r_g_u_m_e_n_t words.
               Thus the command

                    echo a b c

               consists  of  the  _c_o_m_m_a_n_d  _n_a_m_e  `echo' and three
               _a_r_g_u_m_e_n_t words `a', `b' and `c'.  The set of _a_r_g_u_-
               _m_e_n_t_s  after  the  _c_o_m_m_a_n_d  _n_a_m_e is said to be the
               _a_r_g_u_m_e_n_t _l_i_s_t of the command (1.1).

argv           The list of arguments to a command written in  the
               shell language (a shell script or shell procedure)
               is stored in a variable  called  _a_r_g_v  within  the
               shell.   This  name is taken from the conventional
               name in the C programming language (3.4).

background     Commands started without waiting for them to  com-
               plete are called _b_a_c_k_g_r_o_u_n_d commands (2.6).

base           A  filename  is sometimes thought of as consisting
               of a _b_a_s_e part, before any `.' character,  and  an
               _e_x_t_e_n_s_i_o_n  - the part after the `.'.  See _f_i_l_e_n_a_m_e
               and _e_x_t_e_n_s_i_o_n (1.6) and basename (1).

bg             The _b_g command causes a _s_u_s_p_e_n_d_e_d job to  continue
               execution in the _b_a_c_k_g_r_o_u_n_d (2.6).

bin            A  directory  containing  binaries of programs and
               shell scripts to be executed is typically called a
               _b_i_n  directory.   The standard system _b_i_n directo-
               ries are `/bin' containing the most  heavily  used
               commands  and `/usr/bin' which contains most other
               user programs.  Programs developed at UC  Berkeley
               live in `/usr/ucb', while locally written programs
               live in  `/usr/local'.   Games  are  kept  in  the
               directory `/usr/games'.  You can place binaries in
               any directory.  If you wish to execute them often,
               the  name of the directories should be a _c_o_m_p_o_n_e_n_t
               of the variable _p_a_t_h.

break          _B_r_e_a_k is a builtin command used to exit from loops
               within the control structure of the shell (3.7).

breaksw        The _b_r_e_a_k_s_w builtin command is used to exit from a
               _s_w_i_t_c_h control structure, like a _b_r_e_a_k exits  from
               loops (3.7).

builtin        A command executed directly by the shell is called
               a _b_u_i_l_t_i_n command.  Most commands in UNIX are  not
               built into the shell, but rather exist as files in
               _b_i_n directories.  These  commands  are  accessible









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               because  the  directories in which they reside are
               named in the _p_a_t_h variable.

case           A _c_a_s_e command is used as  a  label  in  a  _s_w_i_t_c_h
               statement  in the shell's control structure, simi-
               lar to that of the language C.  Details are  given
               in the shell documentation `csh (1)' (3.7).

cat            The  _c_a_t  program  catenates  a  list of specified
               files on the _s_t_a_n_d_a_r_d _o_u_t_p_u_t.  It is usually  used
               to  look  at  the contents of a single file on the
               terminal, to `cat a file' (1.8, 2.3).

cd             The _c_d command  is  used  to  change  the  _w_o_r_k_i_n_g
               _d_i_r_e_c_t_o_r_y.   With  no  arguments,  _c_d changes your
               _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y to be your _h_o_m_e directory  (2.4,
               2.7).

chdir          The _c_h_d_i_r command is a synonym for _c_d.  _C_d is usu-
               ally used because it is easier to type.

chsh           The _c_h_s_h command is used to change the shell which
               you  use on UNIX.  By default, you use a different
               version of the shell which resides  in  `/bin/sh'.
               You can change your shell to `/bin/csh' by doing

                    chsh your-login-name /bin/csh

               Thus I would do

                    chsh bill /bin/csh

               It  is  only  necessary to do this once.  The next
               time you log in to UNIX after doing this  command,
               you  will  be  using  _c_s_h rather than the shell in
               `/bin/sh' (1.9).

cmp            _C_m_p is a program which compares files.  It is usu-
               ally  used on binary files, or to see if two files
               are identical (3.6).  For comparing text files the
               program _d_i_f_f, described in `diff (1)' is used.

command        A  function performed by the system, either by the
               shell (a builtin _c_o_m_m_a_n_d) or by a program residing
               in  a  file in a directory within the UNIX system,
               is called a _c_o_m_m_a_n_d (1.1).

command name
               When a command is issued, it consists of a _c_o_m_m_a_n_d
               _n_a_m_e, which is the first word of the command, fol-
               lowed by arguments.  The  convention  on  UNIX  is
               that  the  first word of a command names the func-
               tion to be performed (1.1).










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command substitution
               The replacement of a command enclosed in ``' char-
               acters  by  the  text  output  by  that command is
               called _c_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n (4.3).

component      A part of a _p_a_t_h_n_a_m_e  between  `/'  characters  is
               called  a  _c_o_m_p_o_n_e_n_t of that _p_a_t_h_n_a_m_e.  A variable
               which has multiple strings as  value  is  said  to
               have  several  _c_o_m_p_o_n_e_n_ts; each string is a _c_o_m_p_o_-
               _n_e_n_t of the variable.

continue       A builtin command which causes  execution  of  the
               enclosing  _f_o_r_e_a_c_h  or  _w_h_i_l_e loop to cycle prema-
               turely.  Similar to the _c_o_n_t_i_n_u_e  command  in  the
               programming language C (3.6).

control-       Certain special characters, called _c_o_n_t_r_o_l charac-
               ters, are produced by holding down the CONTROL key
               on   your  terminal  and  simultaneously  pressing
               another character, much like the SHIFT key is used
               to  produce  upper case characters. Thus _c_o_n_t_r_o_l_-c
               is produced by holding down the CONTROL key  while
               pressing the `c' key.  Usually UNIX prints a caret
               (^) followed by the corresponding letter when  you
               type  a _c_o_n_t_r_o_l character (e.g. `^C' for _c_o_n_t_r_o_l_-c
               (1.8).

core dump      When a program terminates abnormally,  the  system
               places  an  image  of  its current state in a file
               named `core'.  This _c_o_r_e _d_u_m_p can be examined with
               the  system  debugger  `adb  (1)'  or `sdb (1)' in
               order to determine what went wrong with  the  pro-
               gram  (1.8).   If  the shell produces a message of
               the form

                    Illegal instruction (core dumped)

               (where `Illegal instruction' is only one  of  sev-
               eral possible messages), you should report this to
               the author of the program or a system  administra-
               tor, saving the `core' file.

cp             The _c_p (copy) program is used to copy the contents
               of one file into another file.  It is one  of  the
               most commonly used UNIX commands (1.6).

csh            The  name  of the shell program that this document
               describes.

.cshrc         The file _._c_s_h_r_c in your _h_o_m_e directory is read  by
               each  shell as it begins execution.  It is usually
               used to change the setting of  the  variable  _p_a_t_h
               and  to  set  _a_l_i_a_s  parameters  which are to take
               effect globally (2.1).









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cwd            The _c_w_d variable in the shell holds  the  _a_b_s_o_l_u_t_e
               _p_a_t_h_n_a_m_e  of the current _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y.  It is
               changed by the shell whenever your current _w_o_r_k_i_n_g
               _d_i_r_e_c_t_o_r_y changes and should not be changed other-
               wise (2.2).

date           The _d_a_t_e command prints the current date and  time
               (1.3).

debugging      _D_e_b_u_g_g_i_n_g is the process of correcting mistakes in
               programs and shell scripts.  The shell has several
               options  and variables which may be used to aid in
               shell _d_e_b_u_g_g_i_n_g (4.4).

default:       The label _d_e_f_a_u_l_t_: is  used  within  shell  _s_w_i_t_c_h
               statements,  as  it  is in the C language to label
               the code to be executed if none of the _c_a_s_e labels
               matches the value switched on (3.7).

DELETE         The  DELETE or RUBOUT key on the terminal normally
               causes an interrupt to be sent to the current job.
               Many  users  change  the interrupt character to be
               ^C.

detached       A command that continues running in the _b_a_c_k_g_r_o_u_n_d
               after you logout is said to be _d_e_t_a_c_h_e_d.

diagnostic     An  error  message  produced by a program is often
               referred to as a _d_i_a_g_n_o_s_t_i_c.  Most error  messages
               are not written to the _s_t_a_n_d_a_r_d _o_u_t_p_u_t, since that
               is often directed away  from  the  terminal  (1.3,
               1.5).   Error  messages are instead written to the
               _d_i_a_g_n_o_s_t_i_c _o_u_t_p_u_t which may be directed away  from
               the  terminal,  but usually is not.  Thus _d_i_a_g_n_o_s_-
               _t_i_c_s will usually appear on the terminal (2.5).

directory      A structure which contains files.  At any time you
               are in one particular _d_i_r_e_c_t_o_r_y whose names can be
               printed by the command  _p_w_d.   The  _c_h_d_i_r  command
               will change you to another _d_i_r_e_c_t_o_r_y, and make the
               files in that _d_i_r_e_c_t_o_r_y visible. The _d_i_r_e_c_t_o_r_y  in
               which  you  are  when you first login is your _h_o_m_e
               directory (1.1, 2.7).

directory stack
               The shell saves  the  names  of  previous  _w_o_r_k_i_n_g
               _d_i_r_e_c_t_o_r_i_e_s in the _d_i_r_e_c_t_o_r_y _s_t_a_c_k when you change
               your current _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y via the _p_u_s_h_d  com-
               mand.  The _d_i_r_e_c_t_o_r_y _s_t_a_c_k can be printed by using
               the _d_i_r_s  command,  which  includes  your  current
               _w_o_r_k_i_n_g  _d_i_r_e_c_t_o_r_y  as the first directory name on
               the left (2.7).











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dirs           The _d_i_r_s  command  prints  the  shell's  _d_i_r_e_c_t_o_r_y
               _s_t_a_c_k (2.7).

du             The  _d_u  command  is  a  program (described in `du
               (1)') which prints the number of  disk  blocks  is
               all  directories  below and including your current
               _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y (2.6).

echo           The _e_c_h_o command prints its arguments (1.6,  3.6).

else           The  _e_l_s_e  command  is  part of the `if-then-else-
               endif' control command construct (3.6).

endif          If an _i_f statement is ended with  the  word  _t_h_e_n,
               all  lines  following the _i_f up to a line starting
               with the word _e_n_d_i_f or _e_l_s_e are  executed  if  the
               condition between parentheses after the _i_f is true
               (3.6).

EOF            An _e_n_d-_o_f-_f_i_l_e is generated by the terminal  by  a
               control-d, and whenever a command reads to the end
               of a file which it has been given as input.   Com-
               mands  receiving input from a _p_i_p_e receive an _e_n_d-
               _o_f-_f_i_l_e when the command sending them  input  com-
               pletes.  Most commands terminate when they receive
               an _e_n_d-_o_f-_f_i_l_e.  The shell has an option to ignore
               _e_n_d-_o_f-_f_i_l_e  from  a terminal input which may help
               you keep from logging out accidentally  by  typing
               too many control-d's (1.1, 1.8, 3.8).

escape         A  character `\' used to prevent the special mean-
               ing of a metacharacter is said to _e_s_c_a_p_e the char-
               acter from its special meaning.  Thus

                    echo \*

               will echo the character `*' while just

                    echo *

               will  echo  the  names  of the file in the current
               directory.  In this example, \ _e_s_c_a_p_es `*'  (1.7).
               There  is  also  a  non-printing  character called
               _e_s_c_a_p_e, usually labelled ESC or ALTMODE on  termi-
               nal  keyboards.   Some older UNIX systems use this
               character to indicate that output is  to  be  _s_u_s_-
               _p_e_n_d_e_d.   Most  systems  use control-s to stop the
               output and control-q to start it.

/etc/passwd    This file contains information about the  accounts
               currently  on  the  system.  It consists of a line
               for each account  with  fields  separated  by  `:'
               characters  (1.8).   You  can look at this file by
               saying









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                    cat /etc/passwd

               The commands _f_i_n_g_e_r and _g_r_e_p  are  often  used  to
               search  for information in this file.  See `finger
               (1)',  `passwd(5)',  and  `grep  (1)'   for   more
               details.

exit           The _e_x_i_t command is used to force termination of a
               shell script, and is built into the shell (3.9).

exit status    A command which discovers a  problem  may  reflect
               this  back  to the command (such as a shell) which
               invoked (executed) it.  It does this by  returning
               a  non-zero number as its _e_x_i_t _s_t_a_t_u_s, a status of
               zero being considered `normal  termination'.   The
               _e_x_i_t  command can be used to force a shell command
               script to give a non-zero _e_x_i_t _s_t_a_t_u_s (3.6).

expansion      The replacement of  strings  in  the  shell  input
               which  contain  metacharacters by other strings is
               referred to as the process of _e_x_p_a_n_s_i_o_n.  Thus the
               replacement  of  the  word `*' by a sorted list of
               files in the  current  directory  is  a  `filename
               expansion'.   Similarly  the  replacement  of  the
               characters `!!' by the text of the last command is
               a   `history   expansion'.   _E_x_p_a_n_s_i_o_n_s  are  also
               referred to as _s_u_b_s_t_i_t_u_t_i_o_n_s (1.6, 3.4, 4.2).

expressions    _E_x_p_r_e_s_s_i_o_n_s are used in the shell to  control  the
               conditional  structures  used  in  the  writing of
               shell scripts and in calculating values for  these
               scripts.  The operators available in shell _e_x_p_r_e_s_-
               _s_i_o_n_s are those of the language C (3.5).

extension      Filenames often consist of  a  _b_a_s_e  name  and  an
               _e_x_t_e_n_s_i_o_n separated by the character `.'.  By con-
               vention, groups of related files often  share  the
               same  _r_o_o_t  name.   Thus if `prog.c' were a C pro-
               gram, then the object file for this program  would
               be  stored in `prog.o'.  Similarly a paper written
               with the `-me' nroff macro package might be stored
               in  `paper.me'  while  a formatted version of this
               paper might be kept in `paper.out' and a  list  of
               spelling errors in `paper.errs' (1.6).

fg             The  _j_o_b _c_o_n_t_r_o_l command _f_g is used to run a _b_a_c_k_-
               _g_r_o_u_n_d or _s_u_s_p_e_n_d_e_d job in  the  _f_o_r_e_g_r_o_u_n_d  (1.8,
               2.6).

filename       Each  file  in UNIX has a name consisting of up to
               14 characters and not including the character  `/'
               which  is  used  in _p_a_t_h_n_a_m_e building.  Most _f_i_l_e_-
               _n_a_m_e_s do not begin with  the  character  `.',  and
               contain only letters and digits with perhaps a `.'









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               separating the _b_a_s_e portion of the  _f_i_l_e_n_a_m_e  from
               an _e_x_t_e_n_s_i_o_n (1.6).

filename expansion
               _F_i_l_e_n_a_m_e  _e_x_p_a_n_s_i_o_n  uses  the metacharacters `*',
               `?' and `[' and `]' to provide a convenient mecha-
               nism  for  naming files.  Using _f_i_l_e_n_a_m_e _e_x_p_a_n_s_i_o_n
               it is easy to name all the files  in  the  current
               directory,  or  all files which have a common _r_o_o_t
               name. Other _f_i_l_e_n_a_m_e _e_x_p_a_n_s_i_o_n mechanisms use  the
               metacharacter  `~' and allow files in other users'
               directories to be named easily (1.6, 4.2).

flag           Many UNIX commands accept arguments which are  not
               the  names of files or other users but are used to
               modify the action  of  the  commands.   These  are
               referred  to  as  _f_l_a_g  options, and by convention
               consist of one or more  letters  preceded  by  the
               character  `-'  (1.2).   Thus  the _l_s (list files)
               command has an option `-s' to list  the  sizes  of
               files.  This is specified

                    ls -s


foreach        The  _f_o_r_e_a_c_h  command is used in shell scripts and
               at  the  terminal  to  specify  repetition  of   a
               sequence  of commands while the value of a certain
               shell variable ranges  through  a  specified  list
               (3.6, 4.1).

foreground     When commands are executing in the normal way such
               that the shell  is  waiting  for  them  to  finish
               before prompting for another command they are said
               to be _f_o_r_e_g_r_o_u_n_d _j_o_b_s  or  _r_u_n_n_i_n_g  _i_n  _t_h_e  _f_o_r_e_-
               _g_r_o_u_n_d.   This is as opposed to _b_a_c_k_g_r_o_u_n_d.  _F_o_r_e_-
               _g_r_o_u_n_d jobs can be stopped  by  signals  from  the
               terminal  caused by typing different control char-
               acters at the keyboard (1.8, 2.6).

goto           The shell has a command _g_o_t_o used in shell scripts
               to transfer control to a given label (3.7).

grep           The  _g_r_e_p command searches through a list of argu-
               ment files for a specified string.  Thus

                    grep bill /etc/passwd

               will print each line in the file _/_e_t_c_/_p_a_s_s_w_d which
               contains  the string `bill'.  Actually, _g_r_e_p scans
               for _r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n_s in the sense of  the  edi-
               tors  `ed  (1)'  and  `ex  (1)'.   _G_r_e_p stands for
               `globally  find  _r_e_g_u_l_a_r  _e_x_p_r_e_s_s_i_o_n  and   print'
               (2.4).









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head           The _h_e_a_d command prints the first few lines of one
               or more files.  If you have a bunch of files  con-
               taining  text  which you are wondering about it is
               sometimes useful to run _h_e_a_d with these  files  as
               arguments.   This will usually show enough of what
               is in these files to let you decide which you  are
               interested in (1.5).
               _H_e_a_d  is also used to describe the part of a _p_a_t_h_-
               _n_a_m_e before and including the last `/'  character.
               The  _t_a_i_l of a _p_a_t_h_n_a_m_e is the part after the last
               `/'.  The `:h' and `:t' modifiers allow  the  _h_e_a_d
               or  _t_a_i_l  of a _p_a_t_h_n_a_m_e stored in a shell variable
               to be used (3.6).

history        The _h_i_s_t_o_r_y mechanism of the shell allows previous
               commands  to be repeated, possibly after modifica-
               tion to correct typing mistakes or to  change  the
               meaning  of  the command.  The shell has a _h_i_s_t_o_r_y
               _l_i_s_t where these commands are kept, and a  _h_i_s_t_o_r_y
               variable  which  controls  how  large this list is
               (2.3).

home directory
               Each user has a _h_o_m_e _d_i_r_e_c_t_o_r_y, which is given  in
               your  entry  in  the  password  file, _/_e_t_c_/_p_a_s_s_w_d.
               This is the directory which you are placed in when
               you  first login.  The _c_d or _c_h_d_i_r command with no
               arguments takes you back to this directory,  whose
               name  is recorded in the shell variable _h_o_m_e.  You
               can also access  the  _h_o_m_e  _d_i_r_e_c_t_o_r_i_e_s  of  other
               users in forming filenames using a _f_i_l_e_n_a_m_e _e_x_p_a_n_-
               _s_i_o_n notation and the character `~' (1.6).

if             A conditional command within  the  shell,  the  _i_f
               command  is  used in shell command scripts to make
               decisions about what course of action to take next
               (3.6).

ignoreeof      Normally,  your shell will exit, printing `logout'
               if you type a control-d at a prompt of `% '.  This
               is  the  way  you usually log off the system.  You
               can _s_e_t the _i_g_n_o_r_e_e_o_f variable if you wish in your
               _._l_o_g_i_n  file  and  then  use the command _l_o_g_o_u_t to
               logout.  This is useful if you sometimes  acciden-
               tally  type too many control-d characters, logging
               yourself off (2.2).

input          Many commands on UNIX take  information  from  the
               terminal  or  from  files  which they then act on.
               This information is called _i_n_p_u_t.   Commands  nor-
               mally  read  for  _i_n_p_u_t  from their _s_t_a_n_d_a_r_d _i_n_p_u_t
               which is, by default, the terminal.  This _s_t_a_n_d_a_r_d
               _i_n_p_u_t  can be redirected from a file using a shell
               metanotation  with  the   character   `<'.    Many









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               commands  will  also read from a file specified as
               argument.  Commands placed in _p_i_p_e_l_i_n_e_s will  read
               from  the  output  of  the previous command in the
               _p_i_p_e_l_i_n_e.  The  leftmost  command  in  a  _p_i_p_e_l_i_n_e
               reads  from  the  terminal if you neither redirect
               its _i_n_p_u_t nor give it a filename to use  as  _s_t_a_n_-
               _d_a_r_d  _i_n_p_u_t.  Special mechanisms exist for supply-
               ing input to commands in shell scripts (1.5, 3.8).

interrupt      An _i_n_t_e_r_r_u_p_t is a signal to a program that is gen-
               erated by typing ^C. (On older  versions  of  UNIX
               the  RUBOUT  or DELETE key were used for this pur-
               pose.)  It causes most programs to stop execution.
               Certain  programs,  such as the shell and the edi-
               tors, handle an _i_n_t_e_r_r_u_p_t in special ways, usually
               by  stopping what they are doing and prompting for
               another command.  While  the  shell  is  executing
               another  command and waiting for it to finish, the
               shell does not listen to  _i_n_t_e_r_r_u_p_t_s_.   The  shell
               often wakes up when you hit _i_n_t_e_r_r_u_p_t because many
               commands die when they receive an _i_n_t_e_r_r_u_p_t  (1.8,
               3.9).

job            One  or more commands typed on the same input line
               separated  by  `|'  or  `;'  characters  are   run
               together  and  are  called a _j_o_b.  Simple commands
               run by themselves without any `|' or  `;'  charac-
               ters  are  the simplest _j_o_b_s_.  _J_o_b_s are classified
               as _f_o_r_e_g_r_o_u_n_d, _b_a_c_k_g_r_o_u_n_d, or _s_u_s_p_e_n_d_e_d (2.6).

job control    The builtin functions that control  the  execution
               of  jobs  are  called _j_o_b _c_o_n_t_r_o_l commands.  These
               are _b_g_, _f_g_, _s_t_o_p_, _k_i_l_l (2.6).

job number     When each job is started it is  assigned  a  small
               number  called  a _j_o_b _n_u_m_b_e_r which is printed next
               to the job in the  output  of  the  _j_o_b_s  command.
               This  number,  preceded by a `%' character, can be
               used as an argument to  _j_o_b  _c_o_n_t_r_o_l  commands  to
               indicate a specific job (2.6).

jobs           The  _j_o_b_s command prints a table showing jobs that
               are either running in the _b_a_c_k_g_r_o_u_n_d or  are  _s_u_s_-
               _p_e_n_d_e_d (2.6).

kill           A command which sends a signal to a job causing it
               to terminate (2.6).

.login         The file _._l_o_g_i_n in your _h_o_m_e directory is read  by
               the shell each time you login to UNIX and the com-
               mands there are executed.  There are a  number  of
               commands  which  are  usefully  placed here, espe-
               cially _s_e_t commands to the shell itself (2.1).










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login shell    The shell that is started on  your  terminal  when
               you  login is called your _l_o_g_i_n _s_h_e_l_l.  It is dif-
               ferent from other shells which you may  run  (e.g.
               on shell scripts) in that it reads the _._l_o_g_i_n file
               before reading commands from the terminal  and  it
               reads the _._l_o_g_o_u_t file after you logout (2.1).

logout         The  _l_o_g_o_u_t  command causes a login shell to exit.
               Normally, a login shell will  exit  when  you  hit
               control-d  generating  an  _e_n_d-_o_f-_f_i_l_e_, but if you
               have set _i_g_n_o_r_e_e_o_f in you _._l_o_g_i_n  file  then  this
               will  not  work and you must use _l_o_g_o_u_t to log off
               the UNIX system (2.8).

.logout        When you log off of UNIX the  shell  will  execute
               commands from the file _._l_o_g_o_u_t in your _h_o_m_e direc-
               tory after it prints `logout'.

lpr            The command _l_p_r is the line printer  daemon.   The
               standard  input  of _l_p_r spooled and printed on the
               UNIX line printer.  You can also give _l_p_r  a  list
               of  filenames  as  arguments to be printed.  It is
               most common to use _l_p_r as the last component of  a
               _p_i_p_e_l_i_n_e (2.3).

ls             The  _l_s  (list  files)  command is one of the most
               commonly used UNIX  commands.   With  no  argument
               filenames  it prints the names of the files in the
               current directory.  It has a number of useful _f_l_a_g
               arguments,  and  can  also  be  given the names of
               directories as arguments, in which case  it  lists
               the names of the files in these directories (1.2).

mail           The _m_a_i_l program is used to send and receive  mes-
               sages  from  other  UNIX users (1.1, 2.1), whether
               they are logged on or not.

make           The _m_a_k_e command is used to maintain one  or  more
               related files and to organize functions to be per-
               formed on these files.  In many ways _m_a_k_e is  eas-
               ier  to  use,  and more helpful than shell command
               scripts (3.2).

makefile       The file containing commands for  _m_a_k_e  is  called
               _m_a_k_e_f_i_l_e or _M_a_k_e_f_i_l_e (3.2).

manual         The _m_a_n_u_a_l often referred to is the `UNIX manual'.
               It contains 8 numbered sections with a description
               of  each  UNIX  program  (section  1), system call
               (section 2), subroutine (section 3), device  (sec-
               tion  4), special data structure (section 5), game
               (section 6), miscellaneous item  (section  7)  and
               system  administration program (section 8).  There
               are also supplementary  documents  (tutorials  and









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               reference  guides)  for  individual programs which
               require explanation in  more  detail.   An  online
               version  of  the  _m_a_n_u_a_l is accessible through the
               _m_a_n command.  Its documentation  can  be  obtained
               online via

                    man man

               If  you  can't decide what manual page to look in,
               try the  _a_p_r_o_p_o_s(1)  command.   The  supplementary
               documents are in subdirectories of /usr/doc.

metacharacter
               Many characters which are neither letters nor dig-
               its have special meaning either to the shell or to
               UNIX.  These characters are called _m_e_t_a_c_h_a_r_a_c_t_e_r_s.
               If it is necessary to place  these  characters  in
               arguments  to  commands  without them having their
               special meaning then  they  must  be  _q_u_o_t_e_d.   An
               example  of  a  _m_e_t_a_c_h_a_r_a_c_t_e_r is the character `>'
               which is used to indicate placement of output into
               a  file.   For  the purposes of the _h_i_s_t_o_r_y mecha-
               nism, most unquoted _m_e_t_a_c_h_a_r_a_c_t_e_r_s  form  separate
               words  (1.4).   The appendix to this user's manual
               lists the _m_e_t_a_c_h_a_r_a_c_t_e_r_s in groups by their  func-
               tion.

mkdir          The  _m_k_d_i_r  command is used to create a new direc-
               tory.

modifier       Substitutions with the _h_i_s_t_o_r_y mechanism, keyed by
               the  character  `!'   or  of  variables  using the
               metacharacter `$', are often subjected to  modifi-
               cations,  indicated  by  placing the character `:'
               after the substitution and following this with the
               _m_o_d_i_f_i_e_r  itself.  The _c_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n mecha-
               nism can also be used to perform modification in a
               similar  way,  but  this  notation  is  less clear
               (3.6).

more           The program _m_o_r_e writes a file  on  your  terminal
               allowing you to control how much text is displayed
               at a time.  _M_o_r_e can move through the file screen-
               ful by screenful, line by line, search forward for
               a string, or start again at the beginning  of  the
               file.   It is generally the easiest way of viewing
               a file (1.8).

noclobber      The shell has a variable _n_o_c_l_o_b_b_e_r  which  may  be
               set  in  the  file  _._l_o_g_i_n  to  prevent accidental
               destruction of files by the `>' output redirection
               metasyntax of the shell (2.2, 2.5).











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noglob         The  shell  variable _n_o_g_l_o_b is set to suppress the
               _f_i_l_e_n_a_m_e _e_x_p_a_n_s_i_o_n  of  arguments  containing  the
               metacharacters `~', `*', `?', `[' and `]' (3.6).

notify         The  _n_o_t_i_f_y  command  tells the shell to report on
               the termination of a specific  _b_a_c_k_g_r_o_u_n_d  _j_o_b  at
               the  exact  time  it  occurs as opposed to waiting
               until just before the next prompt  to  report  the
               termination.   The _n_o_t_i_f_y variable, if set, causes
               the shell to  always  report  the  termination  of
               _b_a_c_k_g_r_o_u_n_d jobs exactly when they occur (2.6).

onintr         The  _o_n_i_n_t_r command is built into the shell and is
               used to control the  action  of  a  shell  command
               script when an _i_n_t_e_r_r_u_p_t signal is received (3.9).

output         Many commands in UNIX result in some lines of text
               which  are  called  their  _o_u_t_p_u_t_.  This _o_u_t_p_u_t is
               usually placed on what is known  as  the  _s_t_a_n_d_a_r_d
               _o_u_t_p_u_t  which  is normally connected to the user's
               terminal.   The  shell  has  a  syntax  using  the
               metacharacter  `>'  for  redirecting  the _s_t_a_n_d_a_r_d
               _o_u_t_p_u_t of a command to a file  (1.3).   Using  the
               _p_i_p_e  mechanism  and  the  metacharacter `|' it is
               also possible for the _s_t_a_n_d_a_r_d _o_u_t_p_u_t of one  com-
               mand  to become the _s_t_a_n_d_a_r_d _i_n_p_u_t of another com-
               mand (1.5).  Certain commands  such  as  the  line
               printer daemon _p do not place their results on the
               _s_t_a_n_d_a_r_d _o_u_t_p_u_t but rather in more  useful  places
               such  as on the line printer (2.3).  Similarly the
               _w_r_i_t_e command places its output on another  user's
               terminal  rather  than  its _s_t_a_n_d_a_r_d _o_u_t_p_u_t (2.3).
               Commands also have a _d_i_a_g_n_o_s_t_i_c _o_u_t_p_u_t where  they
               write  their error messages.  Normally these go to
               the terminal even if the _s_t_a_n_d_a_r_d _o_u_t_p_u_t has  been
               sent  to a file or another command, but it is pos-
               sible to direct error diagnostics along with _s_t_a_n_-
               _d_a_r_d _o_u_t_p_u_t using a special metanotation (2.5).

path           The  shell  has  a  variable  _p_a_t_h which gives the
               names of the directories in which it searches  for
               the  commands which it is given.  It always checks
               first to see if the command it is given  is  built
               into the shell.  If it is, then it need not search
               for the command as it can do  it  internally.   If
               the   command  is  not  builtin,  then  the  shell
               searches for a file with the name given in each of
               the  directories  in  the  _p_a_t_h  variable, left to
               right.  Since the normal definition  of  the  _p_a_t_h
               variable is

                    path (. /usr/ucb /bin /usr/bin)

               the shell normally looks in the current directory,









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               and  then  in  the  standard  system   directories
               `/usr/ucb',  `/bin'  and  `/usr/bin' for the named
               command (2.2).  If the command cannot be found the
               shell  will print an error diagnostic.  Scripts of
               shell commands  will  be  executed  using  another
               shell  to  interpret  them  if they have `execute'
               permission set.  This is normally true  because  a
               command of the form

                    chmod 755 script

               was  executed  to  turn this execute permission on
               (3.3).  If you add new commands to a directory  in
               the  _p_a_t_h,  you  should  issue  the command _r_e_h_a_s_h
               (2.2).

pathname       A list of  names,  separated  by  `/'  characters,
               forms a _p_a_t_h_n_a_m_e_.  Each _c_o_m_p_o_n_e_n_t_, between succes-
               sive `/' characters, names a  directory  in  which
               the  next _c_o_m_p_o_n_e_n_t file resides.  _P_a_t_h_n_a_m_e_s which
               begin with the character `/' are interpreted rela-
               tive  to  the  _r_o_o_t  directory  in the filesystem.
               Other _p_a_t_h_n_a_m_e_s are interpreted  relative  to  the
               current  directory  as  reported by _p_w_d_.  The last
               component of a _p_a_t_h_n_a_m_e may name a directory,  but
               usually names a file.

pipeline       A  group of commands which are connected together,
               the _s_t_a_n_d_a_r_d _o_u_t_p_u_t of each connected to the _s_t_a_n_-
               _d_a_r_d _i_n_p_u_t of the next, is called a _p_i_p_e_l_i_n_e_.  The
               _p_i_p_e mechanism used to connect these  commands  is
               indicated  by  the  shell  metacharacter `|' (1.5,
               2.3).

popd           The  _p_o_p_d  command  changes  the  shell's  _w_o_r_k_i_n_g
               _d_i_r_e_c_t_o_r_y  to the directory you most recently left
               using the _p_u_s_h_d command.  It returns to the direc-
               tory  without  having to type its name, forgetting
               the name of the current _w_o_r_k_i_n_g  _d_i_r_e_c_t_o_r_y  before
               doing so (2.7).

port           The part of a computer system to which each termi-
               nal is connected is called a  _p_o_r_t.   Usually  the
               system  has a fixed number of _p_o_r_t_s, some of which
               are  connected  to  telephone  lines  for  dial-up
               access,  and  some  of which are permanently wired
               directly to specific terminals.

pr             The _p_r command is used to prepare listings of  the
               contents  of files with headers giving the name of
               the file and the date and time at which  the  file
               was last modified (2.3).











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printenv       The  _p_r_i_n_t_e_n_v command is used to print the current
               setting of variables in the environment (2.8).

process        An instance of  a  running  program  is  called  a
               _p_r_o_c_e_s_s (2.6).  UNIX assigns each _p_r_o_c_e_s_s a unique
               number when it is started  -  called  the  _p_r_o_c_e_s_s
               _n_u_m_b_e_r.  _P_r_o_c_e_s_s _n_u_m_b_e_r_s can be used to stop indi-
               vidual _p_r_o_c_e_s_s_e_s using the _k_i_l_l or  _s_t_o_p  commands
               when  the  _p_r_o_c_e_s_s_e_s  are part of a detached _b_a_c_k_-
               _g_r_o_u_n_d job.

program        Usually synonymous with _c_o_m_m_a_n_d; a binary file  or
               shell command script which performs a useful func-
               tion is often called a _p_r_o_g_r_a_m.

prompt         Many programs will print a _p_r_o_m_p_t on the  terminal
               when  they expect input.  Thus the editor `ex (1)'
               will print a `:' when it expects input.  The shell
               _p_r_o_m_p_t_s  for input with `% ' and occasionally with
               `? '  when  reading  commands  from  the  terminal
               (1.1).   The shell has a variable _p_r_o_m_p_t which may
               be set to a different value to change the  shell's
               main  _p_r_o_m_p_t.   This is mostly used when debugging
               the shell (2.8).

pushd          The _p_u_s_h_d command, which means  `push  directory',
               changes  the  shell's  _w_o_r_k_i_n_g  _d_i_r_e_c_t_o_r_y and also
               remembers the current _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y before the
               change is made, allowing you to return to the same
               directory  via  the  _p_o_p_d  command  later  without
               retyping its name (2.7).

ps             The  _p_s  command is used to show the processes you
               are currently running.  Each process is shown with
               its  unique  process  number, an indication of the
               terminal name it is attached to, an indication  of
               the  state  of the process (whether it is running,
               stopped,  awaiting  some  event  (sleeping),   and
               whether  it is swapped out), and the amount of CPU
               time it has used so far.  The command  is  identi-
               fied  by  printing  some of the words used when it
               was invoked (2.6).  Shells, such as  the  _c_s_h  you
               use  to run the _p_s command, are not normally shown
               in the output.

pwd            The _p_w_d command prints the full  _p_a_t_h_n_a_m_e  of  the
               current  _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y.  The _d_i_r_s builtin com-
               mand is usually a better and faster choice.

quit           The _q_u_i_t signal, generated by a control-\, is used
               to terminate programs which are behaving unreason-
               ably.  It normally  produces  a  core  image  file
               (1.8).










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quotation      The  process by which metacharacters are prevented
               their special meaning, usually by using the  char-
               acter  `' in pairs, or by using the character `\',
               is referred to as _q_u_o_t_a_t_i_o_n (1.7).

redirection    The routing of input or output from or to  a  file
               is  known as _r_e_d_i_r_e_c_t_i_o_n of input or output (1.3).

rehash         The _r_e_h_a_s_h command tells the shell to rebuild  its
               internal  table  of  which  commands  are found in
               which directories in your _p_a_t_h.  This is necessary
               when  a  new  program is installed in one of these
               directories (2.8).

relative pathname
               A _p_a_t_h_n_a_m_e which does not  begin  with  a  `/'  is
               called a _r_e_l_a_t_i_v_e _p_a_t_h_n_a_m_e since it is interpreted
               _r_e_l_a_t_i_v_e to the current  _w_o_r_k_i_n_g  _d_i_r_e_c_t_o_r_y.   The
               first  _c_o_m_p_o_n_e_n_t of such a _p_a_t_h_n_a_m_e refers to some
               file or directory in the  _w_o_r_k_i_n_g  _d_i_r_e_c_t_o_r_y,  and
               subsequent _c_o_m_p_o_n_e_n_t_s between `/' characters refer
               to directories below the _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y.  _P_a_t_h_-
               _n_a_m_e_s  that  are  not _r_e_l_a_t_i_v_e are called _a_b_s_o_l_u_t_e
               _p_a_t_h_n_a_m_e_s (1.6).

repeat         The _r_e_p_e_a_t  command  iterates  another  command  a
               specified number of times.

root           The  directory  that  is  at the top of the entire
               directory structure is called the  _r_o_o_t  directory
               since  it  is the `root' of the entire tree struc-
               ture of directories.  The name used  in  _p_a_t_h_n_a_m_e_s
               to  indicate  the _r_o_o_t is `/'.  _P_a_t_h_n_a_m_e_s starting
               with `/' are said to be _a_b_s_o_l_u_t_e since they  start
               at  the  _r_o_o_t directory.  _R_o_o_t is also used as the
               part of a _p_a_t_h_n_a_m_e that is left after removing the
               _e_x_t_e_n_s_i_o_n.  See _f_i_l_e_n_a_m_e for a further explanation
               (1.6).

RUBOUT         The RUBOUT or DELETE key is often  used  to  erase
               the  previously typed character; some users prefer
               the BACKSPACE for this purpose.  On older versions
               of UNIX this key served as the INTR character.

scratch file   Files whose names begin with a `#' are referred to
               as _s_c_r_a_t_c_h _f_i_l_e_s,  since  they  are  automatically
               removed  by  the  system after a couple of days of
               non-use, or more frequently if disk space  becomes
               tight (1.3).

script         Sequences  of  shell commands placed in a file are
               called shell command _s_c_r_i_p_t_s.  It is often  possi-
               ble  to  perform  simple tasks using these _s_c_r_i_p_t_s
               without writing a program in a language such as C,









An Introduction to the C shell                           USD:4-63


               by  using  the shell to selectively run other pro-
               grams (3.3, 3.10).

set            The builtin _s_e_t command is used to assign new val-
               ues  to  shell variables and to show the values of
               the current variables.  Many shell variables  have
               special  meaning  to  the  shell  itself.  Thus by
               using the _s_e_t command the behavior  of  the  shell
               can be affected (2.1).

setenv         Variables  in the environment `environ (5)' can be
               changed by using the _s_e_t_e_n_v builtin command (2.8).
               The  _p_r_i_n_t_e_n_v  command  can  be  used to print the
               value of the variables in the environment.

shell          A _s_h_e_l_l is a command language interpreter.  It  is
               possible  to  write  and  run  your  own _s_h_e_l_l, as
               _s_h_e_l_l_s are no different than any other programs as
               far as the system is concerned.  This manual deals
               with the details of one particular  _s_h_e_l_l,  called
               _c_s_h_.

shell script   See _s_c_r_i_p_t (3.3, 3.10).

signal         A  _s_i_g_n_a_l  in UNIX is a short message that is sent
               to a running program  which  causes  something  to
               happen  to  that process.  _S_i_g_n_a_l_s are sent either
               by typing special _c_o_n_t_r_o_l characters on  the  key-
               board  or by using the _k_i_l_l or _s_t_o_p commands (1.8,
               2.6).

sort           The _s_o_r_t program sorts a sequence of lines in ways
               that can be controlled by argument _f_l_a_g_s (1.5).

source         The  _s_o_u_r_c_e  command causes the shell to read com-
               mands from a specified file.  It  is  most  useful
               for  reading  files  such as _._c_s_h_r_c after changing
               them (2.8).

special character
               See _m_e_t_a_c_h_a_r_a_c_t_e_r_s and the appendix to  this  man-
               ual.

standard       We  refer often to the _s_t_a_n_d_a_r_d _i_n_p_u_t and _s_t_a_n_d_a_r_d
               _o_u_t_p_u_t of commands.  See _i_n_p_u_t  and  _o_u_t_p_u_t  (1.3,
               3.8).

status         A  command  normally returns a _s_t_a_t_u_s when it fin-
               ishes.  By convention a _s_t_a_t_u_s of  zero  indicates
               that  the  command succeeded.  Commands may return
               non-zero _s_t_a_t_u_s to  indicate  that  some  abnormal
               event  has occurred.  The shell variable _s_t_a_t_u_s is
               set to the _s_t_a_t_u_s returned by  the  last  command.
               It  is most useful in shell command scripts (3.6).









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stop           The _s_t_o_p command causes a _b_a_c_k_g_r_o_u_n_d job to become
               _s_u_s_p_e_n_d_e_d (2.6).

string         A sequential group of characters taken together is
               called a _s_t_r_i_n_g.  _S_t_r_i_n_g_s can contain  any  print-
               able characters (2.2).

stty           The _s_t_t_y program changes certain parameters inside
               UNIX which determine how your terminal is handled.
               See `stty (1)' for a complete description (2.6).

substitution   The  shell  implements  a  number of _s_u_b_s_t_i_t_u_t_i_o_n_s
               where sequences indicated  by  metacharacters  are
               replaced  by other sequences.  Notable examples of
               this  are  history  _s_u_b_s_t_i_t_u_t_i_o_n  keyed   by   the
               metacharacter  `!' and variable _s_u_b_s_t_i_t_u_t_i_o_n indi-
               cated by `$'.  We also refer to  _s_u_b_s_t_i_t_u_t_i_o_n_s  as
               _e_x_p_a_n_s_i_o_n_s (3.4).

suspended      A  job  becomes  _s_u_s_p_e_n_d_e_d  after a STOP signal is
               sent to it, either by typing a  _c_o_n_t_r_o_l-z  at  the
               terminal  (for  _f_o_r_e_g_r_o_u_n_d  jobs)  or by using the
               _s_t_o_p command (for  _b_a_c_k_g_r_o_u_n_d  jobs).   When  _s_u_s_-
               _p_e_n_d_e_d,  a  job temporarily stops running until it
               is restarted by either the _f_g or _b_g command (2.6).

switch         The  _s_w_i_t_c_h  command of the shell allows the shell
               to select one of a number of sequences of commands
               based on an argument string.  It is similar to the
               _s_w_i_t_c_h statement in the language C (3.7).

termination    When a command which is being executed finishes we
               say  it undergoes _t_e_r_m_i_n_a_t_i_o_n or _t_e_r_m_i_n_a_t_e_s_.  Com-
               mands normally terminate when they read an _e_n_d-_o_f-
               _f_i_l_e from their _s_t_a_n_d_a_r_d _i_n_p_u_t.  It is also possi-
               ble to  terminate  commands  by  sending  them  an
               _i_n_t_e_r_r_u_p_t  or _q_u_i_t signal (1.8).  The _k_i_l_l program
               terminates specified jobs (2.6).

then           The _t_h_e_n command is part of the shell's  `if-then-
               else-endif'  control  construct  used  in  command
               scripts (3.6).

time           The _t_i_m_e command can be used to measure the amount
               of  CPU and real time consumed by a specified com-
               mand as well as the amount  of  disk  i/o,  memory
               used, and number of page faults and swaps taken by
               the command (2.1, 2.8).

tset           The _t_s_e_t program is used to set standard erase and
               kill  characters  and to tell the system what kind
               of terminal you are using.  It is often invoked in
               a _._l_o_g_i_n file (2.1).










An Introduction to the C shell                           USD:4-65


tty            The  word  _t_t_y  is  a  historical abbreviation for
               `teletype' which is frequently  used  in  UNIX  to
               indicate  the  _p_o_r_t  to  which a given terminal is
               connected.  The _t_t_y command will print the name of
               the   _t_t_y  or  _p_o_r_t  to  which  your  terminal  is
               presently connected.

unalias        The _u_n_a_l_i_a_s command removes aliases (2.8).

UNIX           UNIX is an operating system  on  which  _c_s_h  runs.
               UNIX provides facilities which allow _c_s_h to invoke
               other programs such as editors and text formatters
               which you may wish to use.

unset          The _u_n_s_e_t command removes the definitions of shell
               variables (2.2, 2.8).

variable expansion
               See _v_a_r_i_a_b_l_e_s and _e_x_p_a_n_s_i_o_n (2.2, 3.4).

variables      _V_a_r_i_a_b_l_e_s in _c_s_h  hold  one  or  more  strings  as
               value.   The  most  common  use of _v_a_r_i_a_b_l_e_s is in
               controlling the behavior of the shell.  See  _p_a_t_h,
               _n_o_c_l_o_b_b_e_r,  and _i_g_n_o_r_e_e_o_f for examples.  _V_a_r_i_a_b_l_e_s
               such as _a_r_g_v are also used in writing  shell  pro-
               grams (shell command scripts) (2.2).

verbose        The  _v_e_r_b_o_s_e  shell  variable  can be set to cause
               commands to  be  echoed  after  they  are  history
               expanded.  This is often useful in debugging shell
               scripts.  The  _v_e_r_b_o_s_e  variable  is  set  by  the
               shell's _-_v command line option (3.10).

wc             The  _w_c  program  calculates the number of charac-
               ters, words, and lines in the  files  whose  names
               are given as arguments (2.6).

while          The  _w_h_i_l_e  builtin  control  construct is used in
               shell command scripts (3.7).

word           A sequence of characters which forms  an  argument
               to  a  command  is called a _w_o_r_d.  Many characters
               which are neither letters, digits,  `-',  `.'  nor
               `/'  form _w_o_r_d_s all by themselves even if they are
               not surrounded by blanks.  Any sequence of charac-
               ters  may  be  made  into a _w_o_r_d by surrounding it
               with `'' characters except for the characters  `''
               and  `!'  which  require  special treatment (1.1).
               This process  of  placing  special  characters  in
               _w_o_r_d_s  without  their  special  meaning  is called
               _q_u_o_t_i_n_g.

working directory
               At any  given  time  you  are  in  one  particular









USD:4-66                           An Introduction to the C shell


               directory,  called  your  _w_o_r_k_i_n_g _d_i_r_e_c_t_o_r_y.  This
               directory's name is printed by the _p_w_d command and
               the files listed by _l_s are the ones in this direc-
               tory.  You can change  _w_o_r_k_i_n_g  _d_i_r_e_c_t_o_r_i_e_s  using
               _c_h_d_i_r.

write          The  _w_r_i_t_e  command is an obsolete way of communi-
               cating with other users who are logged in to  UNIX
               (you  have to take turns typing).  If you are both
               using display terminals,  use  _t_a_l_k(1),  which  is
               much more pleasant.

















































