Variables in the C shell

The C shell uses two types of variables, environment variables and shell variables to store information about the way it is to operate.

Environment variables are:

• initialized at login
• passed to all processes run from the current shell
• used to store information that other programs may need to know
• usually given upper case identifiers.

Shell variables are:

• initialized by the shell,
• not passed to processes run from the current shell,
• usually given lower case identifiers.

Common environment variables are:

EDITOR

name/location of default editor (used in mail programs etc.)

HOME

home directory

PATH

list of directories to search for programs

PRINTER

name/location of default printer

SHELL

name of shell

TERM

name of terminal device

USER

user identity

VISUAL

is used by many programs for name/location of default editor

Some common shell variables are:

history

number of previous commands stored

home

home directory

ignoreeof

if set, the EOF control sequence will not exit the login shell

notify

if set, the shell will notify any changes in the status of background jobs

path

directories to search for executables

prompt

current shell prompt

savehist

number of history commands to save from one login session to the next

shell

location of shell program

Note, that some variables exist as both environment variables and shell variables, but because the environment version has an upper case identifier and the shell version a lower case identifier they are separate distinct variables. However, for these particular variables (HOME/home, PATH/path and TERM/term) the shell will automatically change both, whichever you set.

When a C shell is started it will set home, path, and term to be the same as the HOME, PATH and TERM environment variables. The shell variable shell will be set to the directory location of the csh executable or whichever shell you are using.

Although most executables look to the environment variables for information about your own personal configurations (for example, the EDITOR environment variable will be used by some mail programs) this is not always guaranteed.

Help: for more information see csh(1) and in this document, on files associated with the C shell.

Environment Variables

The printenv command will list all currently set environment variables. For example,

% printenv
HOME=/u1/mary
SHELL=/bin/csh
PATH=(/u1/mary/bin /bin /usr/bin /usr/local/bin)
USER=mary
TERM=vt100
EDITOR=/usr/local/bin/emacs
PRINTER=central


To add a new variable to the list, or modify an existing one, use the setenv command,

% setenv PRINTER central

To remove an environment variable use the unsetenv command.

% unsetenv PRINTER

Help: for more information see csh(1).

Shell Variables

Set a new shell variable with the set command.

% set message=hello
% echo $message
hello

Note, there are no spaces around the equals sign. The dollar sign, $, tells echo to display the value of the variable message, i.e. hello instead of the string message.

Some shell variables have no parameters, for example set ignoreof simply switches that setting on. Multiple values can be set using () brackets.

A list of the current shell variables can be listed using the command set. Any changes made will only affect the current shell, unless placed in the .cshrc file.

% set
argv ()
message hello
ignoreof
history 40
home /u1/mary
path (/u1/mary/bin /bin /usr/bin /usr/local/bin)
noclobber
shell /bin/csh

To remove a shell variable use unset.

% unset message

Help: for more information see csh(1). See the section on Predefined and Environment variables for explanation of individual shell variables.