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Linux Pocket Guide
book

Linux Pocket Guide

by Daniel J. Barrett
February 2004
Beginner content levelBeginner
200 pages
5h 40m
English
O'Reilly Media, Inc.
Content preview from 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
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Publisher Resources

ISBN: 9780596806347Errata Page