tcsh - Shell Variables

Environment variables are associated with each process, including your shell, and inheritted by children. So, for example, when you invoke a program, such as elm, it inherits all the environment variables from your shell. Environment variables are accessed with the setenv and unsetenv commands, and are by convention given names in upper-case letters, such as PAGER and EDITOR. Environment variables are used on a case-by-case basis to communicate user preferences to application programs. A good example is the newsreader nn, which will look at the value of the environment variable EDITOR to determine which text editor a user likes to use.

Shell variables are internal to tcsh only. They are used to configure the behavoir of various shell commands. Here is a list of some commonly used shell variables:

autologout

The number of minutes of idle time after which the shell automatically terminates and logs you out. This is a security feature in case you leave yourself logged in accidentally. To disable, simply unset the variable.

history

The number of previous commands to save in the history buffer.

ignoreeof

If set, the UNIX EOF character (CTRL-D) will not terminate the shell.

notify

If set, the shell announces job completions asynchronously. The default is to preent job completions just before printing a prompt.

path

The list of directories in which to look for commands. This is the same as the evironment variable PATH; changing either one will update the other one.

prompt

The string to use as a command prompt. tcsh uses escape codes with the "%" key for expansions within the prompt string. Here are a few of the mor useful ones:

• %/ - current directory
• %~ - current directory, with ~-expansions for home directories
• %l - the tty
• %# - the ">" character, usually used at the end of the prompt
• %n - your username
• %M - hostname
• %m - hostname (short form)

For example, I set my prompt to "%n@%m:%~%# ". This results in this example prompt "roth@bifur:~> ".

watch

A list of user/terminal pairs to watch for logins. This is useful to have tcsh notify you when someone you know has logged into your machine.