Master Linux Environment Variables: Permanent and Temporary Settings Explained

What Are Environment Variables?

Linux is a multi‑user operating system where each user has a dedicated environment defined by a set of variables called environment variables. Users can modify these variables to tailor their shell behavior.

How to Set Environment Variables

Permanent Variables for All Users

To make a variable available to every user, edit /etc/profile (only root can modify this file) and add an export line, for example:

# vi /etc/profile
export CLASSPATH=./JAVA_HOME/lib:$JAVA_HOME/jre/lib

After saving, run source /etc/profile to apply the change immediately; otherwise it takes effect at the next login.

Permanent Variables for a Single User

For a specific user, add the export line to ~/.bash_profile (or ~/.bashrc). Example:

# vi /home/rethink/.bash_profile
export CLASSPATH=./JAVA_HOME/lib:$JAVA_HOME/jre/lib
source /home/rethink/.bash_profile

The two files differ: .bash_profile is read once at a login shell start, while .bashrc is read for each interactive non‑login shell.

Temporary Variables (Current Shell Only)

Use the export command directly in the terminal; the variable disappears when the shell exits.

export NAME='rethink'
echo $NAME

Common Environment Variables

PATH – Colon‑separated list of directories searched for executables.

echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

HOME – User's home directory.

echo $HOME
/home/rethink

HISTSIZE – Number of commands stored in history (default 1000).

echo $HISTSIZE
1000
HISTSIZE=1001
echo $HISTSIZE
1001

LOGNAME – Current login name.

echo $LOGNAME
rethink

HOSTNAME – System host name.

echo $HOSTNAME
JDu4e00u53f7

SHELL – Path to the user's default shell.

echo $SHELL
/bin/bash

Useful Commands for Managing Variables

echo

– Print the value of a variable, e.g., echo $NAME. export – Define a new environment variable, e.g., export NAME='rethink'. env – List all environment variables for the current user. set – Show shell variables, including user‑defined ones. unset – Remove a variable, e.g., unset NAME. readonly – Mark a variable as read‑only; it cannot be unset. history – Display command history; use !n to re‑execute command number n.