Bash shell is used for various purposes under Linux. How do I customize the shell environment variable under Linux operating systems?

You can use shell variables to store data, set configuration options and customize the shell environment under Linux. The default shell is Bash under Linux and can be used for the following purposes:

1. Configure look and feel of shell.
2. Setup terminal settings depending on which terminal you’re using.
3. Set the search path such as JAVA_HOME, and ORACLE_HOME.
4. Set environment variables as needed by programs.
5. Run commands that you want to run whenever you log in or log out.
6. Setup aliases and/or shell function to automate tasks to save typing and time.
7. Changing bash prompt.
8. Setting shell options.

You can use the following commands to view and configure the environment.

Display Current Environment

Type the following command:
$ set
Sample outputs:

BASH=/bin/bash
BASH_ARGC=()
BASH_ARGV=()
BASH_LINENO=()
BASH_SOURCE=()
BASH_VERSINFO=([0]="3" [1]="2" [2]="25" [3]="1" [4]="release" [5]="x86_64-redhat-linux-gnu")
BASH_VERSION='3.2.25(1)-release'
COLORS=/etc/DIR_COLORS.xterm
COLUMNS=237
CVS_RSH=ssh
DIRSTACK=()
EUID=0
GROUPS=()
G_BROKEN_FILENAMES=1
HISTFILE=/root/.bash_history
HISTFILESIZE=1000
HISTSIZE=1000
HOME=/root
HOSTNAME=server3.www.p.cyberciti.biz
HOSTTYPE=x86_64
IFS=$' \t\n'
INPUTRC=/etc/inputrc
LANG=en_US.UTF-8
LESSOPEN='|/usr/bin/lesspipe.sh %s'
LINES=64
LOGNAME=root
LS_COLORS='no=00:fi=00:di=00;34:ln=00;36:pi=40;33:so=00;35:bd=40;33;01:cd=40;33;01:or=01;05;37;41:mi=01;05;37;41:ex=00;32:*.cmd=00;32:*.exe=00;32:*.com=00;32:*.btm=00;32:*.bat=00;32:*.sh=00;32:*.csh=00;32:*.tar=00;31:*.tgz=00;31:*.arj=00;31:*.taz=00;31:*.lzh=00;31:*.zip=00;31:*.z=00;31:*.Z=00;31:*.gz=00;31:*.bz2=00;31:*.bz=00;31:*.tz=00;31:*.rpm=00;31:*.cpio=00;31:*.jpg=00;35:*.gif=00;35:*.bmp=00;35:*.xbm=00;35:*.xpm=00;35:*.png=00;35:*.tif=00;35:'
MACHTYPE=x86_64-redhat-linux-gnu
MAIL=/var/spool/mail/root
MAILCHECK=60
OPTERR=1
OPTIND=1
OSTYPE=linux-gnu
PATH=/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin
PIPESTATUS=([0]="0")
PPID=35469
PROMPT_COMMAND='echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/~}"; echo -ne "\007"'
PS1='[\u@\h \W]\$ '
PS2='> '
PS4='+ '
PWD=/root
SHELL=/bin/bash
SHELLOPTS=braceexpand:emacs:hashall:histexpand:history:interactive-comments:monitor
SHLVL=1
SSH_CLIENT='10.1.3.116 44212 22'
SSH_CONNECTION='10.1.3.116 44212 10.10.29.68 22'
SSH_TTY=/dev/pts/0
TERM=xterm
UID=0
USER=root
_=set
consoletype=pty
tmpid=0
genpasswd () 
{ 
    local l=$1;
    [ "$l" == "" ] && l=16;
    tr -dc A-Za-z0-9_ < /dev/urandom | head -c ${l} | xargs
}
xrpm () 
{ 
    [ "$1" != "" ] && ( rpm2cpio "$1" | cpio -idmv )
}

The $PATH defined the search path for commands. It is a colon-separated list of directories in which the shell looks for commands. The $PS1 defines your prompt settings. See the list of all commonly used shell variables for more information. You can display the value of a variable using printf or echo command:
$ echo "$HOME"
OR
$ printf "%s\n" $HOME
Sample outputs:
/home/vivek

Task: Set Environment Variables on Linux

You can modify each environmental or system variable using the export command. Set the PATH environment variable to include the directory where you installed the bin directory with perl and shell scripts:

export PATH=${PATH}:/home/vivek/bin

OR

export PATH=${PATH}:${HOME}/bin

To set the JAVA_HOME environment variable to the directory where you installed the J2SE SDK application, enter:

export PATH=${PATH}:/usr/java/jdk1.5.0_07/bin

You can set multiple paths as follows:

export ANT_HOME=/path/to/ant/dir
export PATH=${PATH}:${ANT_HOME}/bin:${JAVA_HOME}/bin

How Do I Make All Settings permanent?

The ~/.bash_profile ($HOME/.bash_profile) or ~/.prfile file is executed when you login using console or remotely using ssh. Type the following command to edit ~/.bash_profile file, enter:
$ vi ~/.bash_proflle
Append the $PATH settings, enter:
export PATH=${PATH}:${HOME}/bin
Save and close the file.

Set IBM DB2 Instance Name

Type the following command:

export DB2INSTANCE=prod_sales

A Note About /etc/profile File

/etc/profile contains Linux system wide environment and startup programs. It is used by all users with bash, ksh, sh shell. Usually used to set PATH variable, user limits, and other settings for user. It only runs for login shell. If you wanted to make large changes or application specific changes use /etc/profile.d/ directory as explained here and here.

See also:

• Customize the bash shell environments from the Linux shell scripting wiki.
• UNIX: Set Environment Variable