Linux Pocket Guide

Shell variables

You can define variables and their values by assigning them:

$ MYVAR=3

To refer to a value, simply place a dollar sign in front of the variable name:

$ echo $MYVAR
3

Some variables are standard and commonly defined by your shell upon login.

Variable	Meaning
DISPLAY	The name of your X window display
HOME	The name of your home directory
LOGNAME	Your login name
MAIL	Path your incoming mailbox
OLDPWD	Your shell’s previous directory
PATH	Your shell search path: directories separated by colons
PWD	Your shell’s current directory
SHELL	The path to your shell, e.g., /bin/bash
TERM	The type of your terminal, e.g., xterm or vt100
USER	Your login name

To see a shell’s variables, run:

$ printenv

The scope of the variable (i.e., which programs know about it) is, by default, the shell in which it’s defined. To make a variable and its value available to other programs your shell invokes (i.e., subshells), use the export command:

$ export MYVAR

or the shorthand:

$ export MYVAR=3

Your variable is now called an environment variable, since it’s available to other programs in your shell’s “environment.” To make a specific value available to a specific program just once, prepend variable=value to the command line:

$ echo $HOME
/home/smith
$ HOME=/home/sally echo "My home is $HOME"
My home is /home/sally
$ echo $HOME
/home/smith                  The original value is unaffected