Linux - Environment Variable

Environment variables in the bash shell help you in several ways. Certain built-in variables change the shell in ways that make your life a little easier, and you can define other variables to suit your own purposes. Here are some examples of built-in shell variables:

• PS1 defines the shell's command-line prompt.
• HOME defines the home directory for a user.
• PATH defines a list of directories to search through when looking for a command to execute.

To see an environment variable, you make use of the echo command as :

[root@oel11g ~]# echo $PATH
/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin:/root/bin

or with the env command

$ env | grep PATH

To list the current values of all environment variables, issue the command

[root@ebs121 lib]# env
HOSTNAME=ebs121.localdomain
TERM=xterm
SHELL=/bin/bash
HISTSIZE=1000
SSH_CLIENT=192.168.2.2 3886 22
SSH_TTY=/dev/pts/1
USER=root
.........

or

$ env | more

The syntax depends of your shell:

• for the Bourne, Bash, or Korn shell:

To add /sbin to the path, type the export command in a console :

export PATH=$PATH:/sbin

or with two variable

$ TMP=/mount_point/tmp
$ TMPDIR=/mount_point/tmp
$ export TMP TMPDIR

• For the C shell:

% setenv TMP /mount_point/tmp
% setenv TMPDIR /mount_point/tmp

You must change the shell startup script.

unset myEnvironmentVariable

To create your own shell variables. First issue the command

newdir=$HOME/mynewdirectory

and then, regardless of what directory you are in, you can issue

cd $newdir