C shell command descriptions
The C shell provides the following built-in commands.
| Item | Description |
|---|---|
| alias [Name [WordList]] | Displays all aliases if you do not specify any parameters. Otherwise, the command displays the alias for the specified Name. If WordList is specified, this command assigns the value of WordList to the alias Name. The specified alias Name cannot be alias or unalias. |
| bg [%Job ...] | Puts the current job or job specified by Job into the background, continuing the job if it was stopped. |
| break | Resumes running after the end of
the nearest enclosing foreach or while command. |
| breaksw | Breaks from a switch command; resumes after the endsw command. |
| case Label: | Defines a Label in a switch command. |
| cd[Name] | Equivalent to the chdir command (see following description). |
| chdir [Name] | Changes the current directory to that specified
by the Name variable. If you do not specify Name,
the command changes to your home directory. If the value of the Name variable
is not a subdirectory of the current directory and does not begin
with /, ./, or ../,
the shell checks each component of the cdpath shell
variable to see if it has a subdirectory matching the Name variable.
If the Name variable is a shell variable with a
value that begins with a slash (/), the shell tries
this to see if it is a directory. The chdir command
is equivalent to the cd command. |
| continue | Continues execution at the end of
the nearest enclosing while or foreach command. |
| default: | Labels the default case in a switch statement.
The default should come after all other case labels. |
| dirs | Displays the directory stack. |
| echo | Writes character strings to the standard output of the shell. |
| else | Runs the commands that follow the second else in
an if (Expression) then ...else
if (Expression2) then ... else ... endif command
sequence. Note: The else statement is the csh built-in
command when using the if(expr) then ..else ...endif.
If the (expr) is true, then the commands up to
the else statement is executed. If the (expr) is
false, then the commands between the else and endif statement
are executed. Anything in single quotes is taken literally and not
interpreted.
|
| end | Successively sets the Name variable
to each member specified by the List variable and
runs the sequence of Commands between the foreach and
the matching end statements. The foreach and end statements
must appear alone on separate lines. Uses the |
| endif | If the Expression variable is
true, runs the Commands that follow the
first then statement. If the else if Expression2 is
true, runs the Commands that follow the
second then statement. If the else
if Expression2 is false, runs
the Commands that follow the else.
Any number of else if pairs are possible. Only
one endif statement is needed. The else segment
is optional. The words else and endif can
be used only at the beginning of input lines. The if segment
must appear alone on its input line or after an else command. |
| endsw | Successively matches each case label against
the value of the string variable. The string is
command and file name expanded first. Use the pattern-matching characters *, ?,
and [ . . . ] in the case labels,
which are variable-expanded. If none of the labels match before a default label
is found, the execution begins after the default label. The case label
and the default label must appear at the beginning of the line.
The breaksw command causes execution to continue
after the endsw command. Otherwise, control might
fall through the case and default labels, as in the
C programming language. If no label matches and there is no default,
execution continues after the endsw command. |
| eval Parameter . . . | Reads the value of the Parameter variable as input to the shell and runs the resulting command or commands in the context of the current shell. Use this command to run commands generated as the result of command or variable substitution because parsing occurs before these substitutions. |
| exec Command | Runs the specified Command in place of the current shell. |
| exit (Expression) | Exits the shell with either the value of the status shell variable (if no Expression is specified) or with the value of the specified Expression. |
| fg [%Job ...] | Brings the current job or job specified by Job into the foreground, continuing the job if it was stopped. |
| foreach Name (List) Command. . . | Successively sets a Name variable for each member specified by the List variable and a sequence of commands, until reaching an end command. |
| glob List | Displays List using history, variable, and file name expansion. Puts a null character between words and does not include a carriage return at the end. |
| goto Word | Continues to run after the line specified by the Word variable. The specified Word is file name and command expanded to yield a string of the form specified by the Label: variable. The shell rewinds its input as much as possible and searches for a line of the form Label:, possibly preceded by blanks or tabs. |
| hashstat | Displays statistics indicating how successful the hash table has been at locating commands. |
| history [-r | -h] [n] | Displays the history event list. The oldest events are displayed first. If you specify a number n, only the specified number of the most recent events are displayed. The -r flag reverses the order in which the events are displayed so the most recent is displayed first. The -h flag displays the history list without leading numbers. Use this flag to produce files suitable for use with the -h flag of the source command. |
| if (Expression) Command | Runs the specified Command (including
its arguments) if the specified Expression is true.
Variable substitution on the Command variable happens
early, at the same time as the rest of the if statement.
The specified Command must be a simple command
(rather than a pipeline, command list, or parenthesized command list). Note: Input
and output redirection occurs even if the Expression variable
is false and the Command is not executed.
|
| jobs [-l] | Lists the active jobs. With the -l (lowercase L) flag, the jobs command lists process IDs in addition to the job number and name. |
| kill -l | [[-Signal] % Job...|PID...] | Sends either the TERM (terminate) signal or the signal specified by Signal to the specified Job or PID (process). Specify signals either by number or by name (as given in the /usr/include/sys/signal.h file, stripped of the SIG prefix). The -l (lowercase L) flag lists the signal names. |
| limit [-h] [Resource [Max-Use]] | Limits the usage of the specified resource by the
current process and each process it creates. Process resource limits
are defined in the /etc/security/limits file.
Controllable resources are the central processing unit (CPU) time,
file size, data size, core dump size, and memory use. Maximum allowable
values for these resources are set with the mkuser command
when the user is added to the system. They are changed with the chuser command.
Limits are categorized as either soft or hard. Users may increase their soft limits up to the ceiling imposed by the hard limits. You must have root user authority to increase a soft limit above the hard limit, or to change hard limits. The -h flag displays hard limits instead of the soft limits. If a Max-Use parameter is not specified, the limit command displays the current limit of the specified resource. If the Resource parameter is not specified, the limit command displays the current limits of all resources. For more information about the resources controlled by the limit subcommand, see the getrlimit, setrlimit, or vlimit subroutine in the Technical Reference: Base Operating System and Extensions, Volume 1. The Max-Use parameter
for CPU time is specified in the
hh:mm:ss format.
The Max-Use parameter for other resources is specified
as a floating-point number or an integer optionally followed by a
scale factor. The scale factor is k or kilobytes (1024 bytes), m or
megabytes, or b or blocks (the units used by the ulimit subroutine as
explained in the Technical Reference: Base Operating System and Extensions, Volume 2).
If you do not specify a scale factor, k is assumed
for all resources. For both resource names and scale factors, unambiguous
prefixes of the names suffice.Note: This command limits the physical
memory (memory use) available for a process only if there is contention
for system memory by other active processes.
|
| login | Ends a login shell and replaces it with an instance of the /usr/bin/login command. This is one way to log out (included for compatibility with the ksh and bsh commands). |
| logout | Ends a login shell. This command must be used if
the ignoreeof option is set. |
| nice [+n] [Command] | If no values are specified, sets the priority of
commands run in this shell to 24. If the +n flag
is specified, sets the priority plus the specified number. If the +n flag
and Command are specified, runs Command at
priority 24 plus the specified number. If you have root user authority,
you can run the nice statement with a negative
number. The Command always runs in a subshell,
and the restrictions placed on commands in simple if statements
apply. |
| nohup [Command] | Causes hangups to be ignored for the remainder
of the script when no Command is specified. If Command is
specified, causes the specified Command to be run
with hangups ignored. To run a pipeline or list of commands,
put the pipeline or list in a shell script, give the script execute
permission, and use the shell script as the value of the Command variable.
All processes run in the background with an ampersand (&)
are effectively protected from being sent a hangup signal when
you log out. However, these processes are still subject to explicitly
sent hangups unless the nohup statement
is used. |
| notify [%Job...] | Causes the shell to notify you asynchronously when the status of the current job or specified Job changes. Normally, the shell provides notification just before it presents the shell prompt. This feature is automatic if the notify shell variable is set. |
| onintr [- | Label] | Controls the action of the shell on interrupts.
If no arguments are specified, restores the default action of the
shell on interrupts, which ends shell scripts or returns to the command
input level. If a - flag is specified, causes all interrupts
to be ignored. If Label is specified, causes
the shell to run a goto Label statement
when the shell receives an interrupt or when a child process ends
due to an interruption. In any case, if the shell is running detached
and interrupts are being ignored, all forms of the onintr statement
have no meaning. Interrupts continue to be ignored by the shell and
all invoked commands. |
| popd [+n] | Pops the directory stack and changes to the new top directory. If you specify a +n variable, the command discards the nth entry in the stack. The elements of the directory stack are numbered from the top, starting at 0. |
| pushd [+n|Name] | With no arguments, exchanges the top two elements of the directory stack. With the Name variable, the command changes to the new directory and pushes the old current directory (as given in the cwd shell variable) onto the directory stack. If you specify a +n variable, the command rotates the nth component of the directory stack around to be the top element and changes to it. The members of the directory stack are numbered from the top, starting at 0. |
| rehash | Causes recomputation of the internal hash table of the contents of the directories in the path shell variable. This action is needed if new commands are added to directories in the path shell variable while you are logged in. The rehash command is necessary only if commands are added to one of the user's own directories or if someone changes the contents of one of the system directories. |
| repeat Count Command | Runs the specified Command, subject
to the same restrictions as commands in simple if statements,
the number of times specified by Count. Note: I/O
redirections occur exactly once, even if the Count variable
equals 0.
|
| set [[Name[n]] [ = Word]] | [Name = (List)] | Shows the value of all shell variables when used with no arguments. Variables that have more than a single word as their value are displayed as a parenthesized word list. If only Name is specified, the C shell sets the Name variable to the null string. Otherwise, sets Name to the value of the Word variable, or sets the Name variable to the list of words specified by the List variable. When n is specified, the nth component of the Name variable is set to the value of the Word variable; the nth component must already exist. In all cases, the value is command and file name expanded. These arguments may be repeated to set multiple values in a single set command. However, variable expansion happens for all arguments before any setting occurs. |
| setenvName Value | Sets the value of the environment variable specified by the Name variable to Value, a single string. The most commonly used environment variables, USER, TERM, HOME, and PATH, are automatically imported to and exported from the C shell variables user, term, home, and path. There is no need to use the setenv statement for these. |
| shift [Variable] | Shifts the members of the argv shell variable or the specified Variable to the left. An error occurs if the argv shell variable or specified Variable is not set or has less than one word as its value. |
| source[-h] Name | Reads commands written in the Name file. You can nest the source commands. However, if they are nested too deeply, the shell might run out of file descriptors. An error in a source command at any level ends all nested source commands. Normally, input during source commands is not placed on the history list. The -h flag causes the commands to be placed in the history list without executing them. |
| stop [%Job ...] | Stops the current job or specified Job running in the background. |
| suspend | Stops the shell as if a STOP signal had been received. |
| switch (string) | Starts a switch (String) case String : ... breaksw default: ... breaksw endsw command sequence. This command sequence successively matches each case label against the value of the String variable. If none of the labels match before a default label is found, the execution begins after the default label. |
| time [Command] | The time command controls automatic
timing of commands. If you do not specify the Command variable,
the time command displays a summary of time used
by this shell and its children. If you specify a command with the Command variable,
it is timed. The shell then displays a time summary, as described
under the time shell
variable. If necessary, an extra shell is created to display the time
statistic when the command completes. The following example uses time with
the sleep command:
The
output from this command looks similar to the following:
The output fields are as follows:
|
| umask [Value] | Determines file permissions. This Value, along with the permissions of the creating process, determines a file's permissions when the file is created. The default is 022. The current setting will be displayed if no Value is specified. |
| unalias *|Pattern | Discards all aliases with names that match the Pattern variable. All aliases are removed by the unalias * command. The absence of aliases does not cause an error. |
| unhash | Disables the use of the internal hash table to locate running programs. |
| unlimit [-h][Resource] | Removes the limitation on the Resource variable.
If no Resource variable is specified, all resource
limitations are removed. See the description of the limit command
for the list of Resource names. The -h flag removes corresponding hard limits. Only a user with root user authority can change hard limits. |
| unset *|Pattern | Removes all variables with names that match the Pattern variable. Use unset * to remove all variables. If no variables are set, it does not cause an error. |
| unsetenvPattern | Removes all variables from the environment whose name matches the specified Pattern. (See the setenv built-in command.) |
| wait | Waits for all background jobs. If the shell is interactive, an INTERRUPT (usually the Ctrl-C key sequence) disrupts the wait. The shell then displays the names and job numbers of all jobs known to be outstanding. |
| while (Expression) Command. . . end | Evaluates the Commands between the while and the matching end statements while the expression specified by the Expression variable evaluates nonzero. You can use the break statement to end and the continue statement to continue the loop prematurely. The while and end statements must appear alone on their input lines. If the input is from a terminal, prompts occur after the while (Expression) similar to the foreach statement. |
| @ [Name[n] = Expression] | Displays the values of all the shell variables when
used with no arguments. Otherwise, sets the name specified by the Name variable
to the value of the Expression variable. If the
expression contains <, >, &,
or | characters, this part of the expression must
be placed within parentheses. When n is
specified, the nth component
of the Name variable is set to the Expression variable.
Both the Name variable and its nth component
must already exist. C language operators, such as |