How to Set Permanent and Temporary Linux Environment Variables for Bash and Csh

Linux environment variables can be defined as permanent (persisting across reboots) or temporary (valid only for the current shell session). The method varies with the shell type, so you must first identify the active shell using echo $SHELL. The article walks through four common scenarios: Bash permanent, Bash temporary, Csh permanent, and Csh temporary.

1. Bash – Permanent Variables (All Users / Single User)

Step 1: Run echo $SHELL to confirm the shell is /bin/bash.

Step 2 (single user): Add export VARIABLE=value to .profile in the user’s home directory (create the file if it does not exist).

Step 3 (all users): Add the same export VARIABLE=value line to /etc/profile for system‑wide effect.

Step 4: Apply the changes with source .profile (or re‑login for /etc/profile).

Step 5: Verify the variable with echo $VARIABLE.

$ echo $SHELL            # shows /bin/bash
$ vi .profile          # add: export ORACLE_HOME=/home/oracle/base
$ source .profile
$ echo $ORACLE_HOME    # /home/oracle/base
$ sudo vi /etc/profile # add: export ORACLE_HOME=/home/oracle/base
$ source /etc/profile   # or re‑login
$ echo $ORACLE_HOME

2. Bash – Temporary Variables

Step 1: Confirm the shell with echo $SHELL.

Step 2: Set a variable for the current session using export VARIABLE=value. This variable disappears after the terminal is closed.

Step 3: Verify with echo $VARIABLE.

$ echo $SHELL
/bin/bash
$ export ORACLE_BASE="/opt/oracle/base"
$ echo $ORACLE_BASE
/opt/oracle/base

3. Csh – Permanent Variables

Step 1: Check the shell with echo $SHELL (should be /usr/bin/csh).

Step 2 (single user): Add setenv VARIABLE value to .cshrc in the user’s home directory (create the file if missing).

Step 3: Apply the changes with source .cshrc.

Step 4: Verify with echo $VARIABLE.

$ echo $SHELL            # shows /usr/bin/csh
$ vi .cshrc            # add: setenv ORACLE_HOME /home/oracle/base
$ source .cshrc
$ echo $ORACLE_HOME    # /home/oracle/base

4. Csh – Temporary Variables

Step 1: Confirm the shell with echo $SHELL.

Step 2: Set a variable for the current session using the syntax set VARIABLE=value (or simply VARIABLE=value in csh). The variable is lost after the session ends.

Step 3: Verify with echo $VARIABLE.

$ echo $SHELL
/usr/bin/csh
$ ORACLE_BASE="/opt/oracle/base"
$ echo $ORACLE_BASE
/opt/oracle/base

By following these steps, you can reliably manage environment variables on Linux regardless of the shell or scope required.