Master Linux Environment Variables: Permanent and Temporary Settings

What are environment variables?

Linux is a multi‑user operating system; each logged‑in user gets a personal environment defined by a set of variables.

Setting permanent variables for all users

Modify the system‑wide file /etc/profile as root. Example:

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

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

Setting permanent variables for a single user

Edit the hidden file ~/.bash_profile (or ~/.bashrc) in the user’s home directory. Example:

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

.bash_profile

is read by login shells, while .bashrc is read by non‑login interactive shells; both can be used to set user‑specific variables.

Temporary variables (current shell only)

Define them directly in the terminal; they disappear when the shell exits.

export NAME="rethink"
echo $NAME

Common commands for environment variables

echo $NAME

– display the value of a variable. export NAME='value' – create or modify a variable. env – list all environment variables. set – list shell variables (including user variables). unset NAME – delete a variable. readonly NAME – make a variable read‑only (cannot be unset).

Typical environment variables

PATH – colon‑separated list of directories searched for executable programs. export PATH=$PATH:$PWD HOME – the user’s home directory. echo $HOME HISTSIZE – number of commands stored in the command history (default 1000).

echo $HISTSIZE
HISTSIZE=1001
echo $HISTSIZE

LOGNAME – the login name of the current user. echo $LOGNAME HOSTNAME – the machine’s network name. echo $HOSTNAME SHELL – the path to the current shell executable.

echo $SHELL