Commands Reference, Volume 1

csh Command

Purpose

Invokes the C shell.

Syntax

csh [ -v | -V ] [ -x | -X ] [ -e ] [ -f ] [ -i ] [ -n ] [ -c String | -s | -t ] [ -b ] [ File [ Parameter ] ]

Description

The C shell is an interactive command interpreter and a command programming language that uses syntax similar to the C programming language. The shell carries out commands either interactively from a terminal keyboard or from a file. The csh command invokes the C shell.

When you invoke the csh command, it begins by looking in your home directory and executing commands from the .cshrc file (used to store customized user information) if it exists. If the csh command runs as a login shell, it executes commands from your .cshrc and .login files.

After the shell processes flag arguments, if neither the -i, -c, -s, nor -t flag is specified and the File [Parameter] is specified, then the shell executes the script file identified by the File [Parameter], including any parameters specified. The script file specified must have read permission; the shell ignores any setuid and setgid settings.

Note: You should not specify a script file if you use the csh command with either the -c or -s flag.

If you specify a script file, the command opens the file and saves the script file name for possible resubstitution by $0 (dollar sign, zero). The script will then be carried out by csh. Remaining parameters initialize the argv variable.

Notes:

If C shell is already running, the .cshrc file can be read again by typing source Pathname, where the Pathname parameter is the path to the .cshrc file.

To avoid problems with remote operations, the .cshrc file should not contain any functions that echo output unless they test for the $prompt variable, which signifies that the shell is interactive. Otherwise, whenever a remote system uses the exec command on a command sent by the local system, both the command and the shell are carried out. For example, exec csh rcp -t Filename executes the .cshrc file and treats the echoed output as the expected response. An if clause can be used to check for the $prompt variable.

Flags

If the first argument to a shell is a - (minus sign), that shell is a login shell. The C shell flags are interpreted as follows:

-b	Forces a break from option processing, causing any further shell arguments to be treated as non-option arguments. This flag can be used to pass options to a shell script without confusion or possible subterfuge. The shell cannot run a script whose real and effective user and group IDs differ without this flag.
-c	Reads commands from the following single argument, which must be present. Any remaining arguments are placed in the argv variable.
-e	Exits if any invoked command ends abnormally or yields a nonzero exit status.
-f	Starts the C shell without searching for or running commands from the .cshrc file in your home directory.
-i	Prompts for its top-level input (an interactive shell), even if input does not appear to be coming from a workstation. Shells are interactive without this flag if their input and output are attached to workstations.
-n	Parses commands but does not run them. This flag aids you in syntactic checking of shell procedures.
-s	Takes command input from standard input.
-t	Reads and processes a single line of input. You can use a \ (backslash) to escape the new-line character at the end of the current line and continue onto another line.
-V	Sets the verbose shell variable before the .cshrc file runs.
-v	Sets the verbose shell variable, so that command input is echoed after history substitution.
-X	Sets the echo shell variable even before the .cshrc file runs.
-x	Sets the echo shell variable, so that commands are echoed after all substitutions and immediately before they run.

Files

$HOME/.cshrc	Read at the beginning of execution by each shell. The .cshrc file is user-defined.
$HOME/.login	Read by the login shell after the .cshrc file at login.
$HOME/.logout	Read by the login shell at logoff.
/usr/bin/sh	Contains the path to the default shell.
/tmp/sh*	Contains the temporary file for <<.
/etc/passwd	Contains the source of home directories for the ~File parameter.

Related Information

The bsh command, chuser command, ksh command, sh command.

The environment file.

C Shell in AIX 5L Version 5.2 System User's Guide: Operating System and Devices.