Master Linux Environment Variables: Set, Update, and Use Them Effectively

Linux is a multi‑user operating system; each logged‑in user has a dedicated environment defined by environment variables that can be customized.

Methods to set environment variables

Permanent variables for all users

These variables apply system‑wide; they are defined in files that only root can modify.

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

After adding, run source /etc/profile to apply immediately; otherwise they take effect on next login.

Permanent variables for a single user

Add variables to the hidden .bash_profile (or .bashrc) in the user’s home directory.

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

.bash_profile is read once at login, while .bashrc is read for each new interactive non‑login shell.

Thus .bash_profile runs only on login, whereas .bashrc runs on every terminal session.

Temporary variables (current shell only)

These exist only for the current shell session and disappear after logout or terminal close.

Set them directly with export VAR=value.

export NAME=example
echo $NAME

Common commands for environment variables

echo – display a variable, e.g., echo $NAME

export – create a new variable, e.g., export NAME='rethink'

Update – assign a new value, e.g., NAME='test'

env – list current user variables

set – list shell variables (includes user variables)

unset – remove a variable, e.g., unset NAME

readonly – make a variable read‑only; readonly NAME prevents unset

Common environment variables

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

PATH contains colon‑separated directories where the shell searches for executable programs; adding a directory makes commands in that location runnable without full paths.

# pwd
/root/docker/httpd
export PATH=$PATH:$PWD
echo $PATH

HOME – user’s default working directory

echo $HOME
/home/rethink

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

echo $HISTSIZE
1000
HISTSIZE=1001
echo $HISTSIZE

History is kept in memory; use history to view, and !n to re‑execute command number n.

history 5
!62

LOGNAME – current login name

echo $LOGNAME
rethink

HOSTNAME – system’s host name

echo $HOSTNAME
JDu4e00u53f7

SHELL – path to the current shell

echo $SHELL
/bin/bash