Customize the bash shell environments

• Strictly speaking there are two types of shell variables:
  1. Local variables (shell variable) - Used by shell and or user scripts. All user created variables are local unless exported using the export command.
  2. Environment variables - Used by shell or user but they are also passed onto other command. Environment variables are passed to subprocesses or subshells.

How do I configure and customize the Bash shell environment?

• Your Bash shell can be configured using the following:
  1. Variables
  2. set command
  3. shopt command
  4. Functions
  5. Alias

What should I put in shell starup files for customization?

A typically Linux or UNIX user do the following:

• Setup a custom prompt.
• Setup terminal settings depending on which terminal you're using.
• Set the search path such as JAVA_HOME, and ORACLE_HOME.
• Set environment variables as needed by programs.
• Run commands that you want to run whenever you log in or log out.

How do I view local variables?

Use the set built-in command to view all variables:

set

Usually, all upper-case variables are set by bash. For example,

echo $SHELL
echo $MAIL

How do I export local variables?

Use the export command:

export EDITOR=/usr/bin/vim
# export DISPLAY environment variable and run xeyes 
export DISPLAY=localhost:11.0 xeyes

Be careful when changing the shell variables. For a complete list of variables set by shell, read the man page for bash by typing the following command:

man bash

How do I view environment variables?

Use the env command to view all environment variables:

env

Sample outputs:

ORBIT_SOCKETDIR=/tmp/orbit-vivek
SSH_AGENT_PID=4296
GPG_AGENT_INFO=/tmp/gpg-ElCDl5/S.gpg-agent:4297:1
TERM=xterm
SHELL=/bin/bash
XDG_SESSION_COOKIE=186611583e30fed08439ca0047067c9d-1255929792.297209-1700262470
GTK_RC_FILES=/etc/gtk/gtkrc:/home/vivek/.gtkrc-1.2-gnome2
WINDOWID=48252673
GTK_MODULES=canberra-gtk-module
USER=vivek
SSH_AUTH_SOCK=/tmp/keyring-s4fcR1/socket.ssh
GNOME_KEYRING_SOCKET=/tmp/keyring-s4fcR1/socket
SESSION_MANAGER=local/vivek-desktop:/tmp/.ICE-unix/4109
USERNAME=vivek
DESKTOP_SESSION=gnome
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
GDM_XSERVER_LOCATION=local
PWD=/home/vivek
LANG=en_IN
GDM_LANG=en_IN
GDMSESSION=gnome
SHLVL=1
HOME=/home/vivek
GNOME_DESKTOP_SESSION_ID=this-is-deprecated
LOGNAME=vivek
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-16XVNAMkFB,guid=0acb6a08e3992ccc7338726c4adbf7c3
XDG_DATA_DIRS=/usr/local/share/:/usr/share/:/usr/share/gdm/
WINDOWPATH=7
DISPLAY=:0.0
COLORTERM=gnome-terminal
XAUTHORITY=/home/vivek/.Xauthority
OLDPWD=/usr/share/man
_=/usr/bin/env

Common Environment Variables

• HOME - Your home directory path.
• PATH - Set your executable search path.
• PWD - Your current working directory.
• See more standard environment variables list.

How do I locate command?

The which command displays the pathnames of the files which would be executed in the current environment. It does this by searching the PATH for executable files matching the names of the arguments.

which command-name

Show fortune command path which print a random, hopefully interesting, adage on screen. Type the following command:

which fortune

Sample output:

/usr/games/fortune

Display your current PATH:

echo $PATH

Sample outputs:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

Customize your PATH variable and remove /usr/games from PATH:

export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Now, try searching fortune command path, enter:

which fortune

Try executing fortune command:

fortune

Sample outputs:

-bash: fortune: command not found

The fortune command could not be located because '/usr/games' is not included in the PATH environment variable. You can type full command path (/usr/games/fortune) or simply add /usr/games to PATH variable:

export PATH=$PATH:/usr/games
fortune

Sample outputs:

Your lucky number has been disconnected.

whereis command

The whereis command is used to locate the binary, source, and manual page files for a command.

whereis command-name
whereis ls

Sample outputs:

ls: /bin/ls /usr/share/man/man1/ls.1.gz

whatis command

The whatis command is used display a short description about command. whatis command searches the manual page names and displays the manual page descriptions for a command:

whatis command-name
whatis date
whatis ifconfig
whatis ping

Sample outputs:

date (1)             - print or set the system date and time
ifconfig (8)         - configure a network interface
ping (8)             - send ICMP ECHO_REQUEST to network hosts