Fedora Linux

PRELINK_FULL_TIME_INTERVAL=14
PRELINK_NONRPM_CHECK_INTERVAL=7
PRELINK_OPTS=-mR
PROMPT_COMMAND='echo -ne '33]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/~}'; echo -ne '07''
PS1='$ '
PS2='> '
PS4='+ '
PWD=/etc
QTDIR=/usr/lib/qt-3.3
QTINC=/usr/lib/qt-3.3/include
QTLIB=/usr/lib/qt-3.3/lib
SESSION_MANAGER=local/beige.fedorabook.com:/tmp/.ICE-unix/2621
SHELL=/bin/bash
SHELLOPTS=braceexpand:emacs:hashall:histexpand:history:interactive-comments:monitor
SHLVL=2
SSH_AGENT_PID=2659
SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpass
SSH_AUTH_SOCK=/tmp/ssh-dNhrfX2621/agent.2621
TERM=xterm
UID=503
USER=hank
USERNAME=hank
WINDOWID=58721388
XAUTHORITY=/home/hank/.Xauthority
_=
qt_prefix=/usr/lib/qt-3.3

Many of these variables contain settings for particular programs. Some of the common variables used by many programs are shown in Table 4-16.

Table 4-16. Key environment variables

Name	Purpose	Format
DISPLAY	Information on which X display is being used	hostname:display.screen hostname is the hostname or IP address of the X server or blank for the local host, display is the display number, and screen is the screen number (optional; the screen number specifies the monitor in a multimonitor, single-person display configuration).
HOME	Home directory	Absolute pathname of the user's home directory.
HOSTNAME	Name of this computer	Fully qualified domain name of the local host.
MAIL	Location of the user's default mailbox	Absolute pathname of the user's mailbox (usually /var/spool/mail/<username>).
PATH	List of directories to be searched to find a command	Absolute pathnames of directories to be searched, separated by colons.
PS1, PS2	Primary and secondary shell prompts	Plain text. Special characters sequences consisting of and a letter are replaced with other information; for example, w is replaced by the current working directory (see the manpage for bash for a complete list).
TERM	Model number of the current terminal	Must correspond to a filename in /usr/share/terminfo/?/*.

To set a shell variable, type the variable name, an equal sign, and the value you wish to assign (all values are treated as text):

$ A= red

Once a variable has been assigned a value, you can use it in commands, preceded by a dollar sign:

$ ls -l red
ls: red: No such file or directory
$ touch $A
$ ls -l red
-rw-r--r-- 1 hank hank 0 Jul 18 15:26 red

The echo command can be used to view the value of a variable:

$ echo $A
red

To destroy a variable, use the unset command: