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In this lesson, you’ll learn how to view, customize, and persist environment variables on Linux. We cover session-level tweaks, system-wide settings, and automating tasks at login.

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What Are Environment Variables?

Environment variables are key–value pairs that your shell and applications use to determine behavior, file locations, and settings. You can list all of them with either: 
printenv
env
Example output: 
$ env
PATH=/home/aaron/.local/bin:/home/aaron/bin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin
HISTSIZE=1000
GJS_DEBUG_TOPICS=JS ERROR;JS LOG
SESSION_MANAGER=local/unix:@/tmp/.ICE-unix/2260,unix/unix:/tmp/.ICE-unix/2260

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Modifying Bash History Size

By default, HISTSIZE=1000 limits your Bash history to 1 000 commands. To increase it for the current session: 
export HISTSIZE=2000
Verify: 
history
Sample: 
    1  sudo nano -w /etc/hosts
    2  ssh [email protected]
    3  ssh student@LFCS-CentOS2
    4  ls
    5  ls -laF
    6  cd .ssh
    7  ls
    8  nano -w known_hosts
    9  exit
   10  rm .ssh/known_hosts

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Common Environment Variables

Here are a few variables you’ll encounter frequently:
VariableDescriptionExample Usage
HOMECurrent user’s home directoryecho $HOME
PWDCurrent working directoryecho $PWD
PATHDirectories to search commandsecho $PATH
HISTSIZEMax number of history entriesecho $HISTSIZE
To display a variable’s value: 
echo $HOME
# /home/aaron
Use these expansions for platform-independent scripting: 
touch "$HOME/saved_file"
Each user running this command will create saved_file in their own home directory.

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Setting Persistent Environment Variables

User-specific variables can go in ~/.bashrc or ~/.profile, but for system-wide settings, use /etc/environment.
Line-based syntax only—no shell expansions or functions.
Example entries look like KEY="value".

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Edit /etc/environment

  1. Open the file with root privileges: 
    sudo vim /etc/environment
  2. Add your variable: 
    KODEKLOUD="https://kodekloud.com"
  3. Save and exit.
  4. Log out and back in, then verify: 
    echo $KODEKLOUD
# https://kodekloud.com
Changes in /etc/environment affect all users and services.
Always back up /etc/environment before editing.

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Automating Commands on Login

To execute commands for every user at login, place shell scripts in /etc/profile.d/. For instance, record the last login time:
  1. Create a script file: 
    sudo vim /etc/profile.d/lastlogin.sh
  2. Add the following (no shebang required): 
    echo "Your last login was at:" > "$HOME/lastlogin"
date >> "$HOME/lastlogin"
  3. Save and exit.
  4. Log out and back in, then check: 
    ls | grep lastlogin
# lastlogin

cat lastlogin
# Your last login was at:
# Thu Dec 16 10:42:37 UTC 2021
This script uses $HOME and demonstrates how to run tasks automatically upon user login.

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