Master Linux Environment Variables: How to Set, Update, and Use Them

Linux is a multi‑user operating system, and each user has a personal environment defined by a set of environment variables that can be modified to suit individual needs.

How to Set Environment Variables

Permanent variables that affect all users

These variables are effective system‑wide; only the root user can modify the corresponding file.

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

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

Permanent variables that affect a single user

Add variables to the hidden .bash_profile file in the user’s home directory (visible with ls -a).

$ whoami
rethink

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

$ source /home/rethink/.bash_profile

The files .bash_profile (executed on login shells) and .bashrc (executed on each new interactive non‑login shell) can both be used; the former is read once at login, the latter at every new terminal session.

Temporary variables are valid only for the current shell session and disappear when the shell exits.

export NAME="rethink"
echo $NAME
rethink

Common Environment Variables

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

The PATH variable lists directories separated by colons where the shell searches for executable programs.

$ pwd
/root/docker/httpd
export PATH=$PATH:$PWD
echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin:/root/docker/httpd

HOME – the user’s home directory

$ whoami
rethink
echo $HOME
/home/rethink

HISTSIZE – number of commands saved in history (default 1000)

echo $HISTSIZE
1000
HISTSIZE=1001
echo $HISTSIZE
1001

History commands are stored in memory and can be viewed with history. Use !n to re‑execute command number n.

history 5
   59  ls
   60  who
   61  history | head -n 5
   62  who am i
   63  history 5
!62
who am i
root     pts/0        2018-04-04 11:00 (101.81.92.18)

LOGNAME – current login name

echo $LOGNAME
rethink

HOSTNAME – host name of the machine

echo $HOSTNAME
JDu4e00u53f7

SHELL – path to the current shell

echo $SHELL
/bin/bash