Work on the Command Line Part 2 Modify shell environment and variables

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.

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

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

Common Environment Variables

Here are a few variables you’ll encounter frequently:

Variable	Description	Example Usage
HOME	Current user’s home directory	`echo $HOME`
PWD	Current working directory	`echo $PWD`
PATH	Directories to search commands	`echo $PATH`
HISTSIZE	Max number of history entries	`echo $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.

Setting Persistent Environment Variables

User-specific variables can go in ~/.bashrc or ~/.profile, but for system-wide settings, use /etc/environment.

Note

Line-based syntax only—no shell expansions or functions.
Example entries look like KEY="value".

Edit `/etc/environment`

Open the file with root privileges:
```
sudo vim /etc/environment
```
Add your variable:
```
KODEKLOUD="https://kodekloud.com"
```
Save and exit.

Log out and back in, then verify:

echo $KODEKLOUD
# https://kodekloud.com

Warning

Changes in /etc/environment affect all users and services.
Always back up /etc/environment before editing.

To execute commands for every user at login, place shell scripts in /etc/profile.d/. For instance, record the last login time:

Create a script file:
```
sudo vim /etc/profile.d/lastlogin.sh
```

Add the following (no shebang required):

echo "Your last login was at:" > "$HOME/lastlogin"
date >> "$HOME/lastlogin"

Save and exit.

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.

Links and References

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