Environment Variables in Linux — Configuring the Linux Environment¶

Environment variables are dynamic values maintained by the operating system that influence how programs, shells, and scripts behave. They store information such as user details, executable paths, language settings, application configurations, and runtime parameters. Environment variables are fundamental to Linux administration, shell scripting, DevOps, Docker, Kubernetes, and cloud computing.

Learning Path¶

Linux Mastery → Module 5: Users and Groups → Lesson 5

Difficulty: Beginner → Intermediate

Reading Time: 55 Minutes

Course Progress

Course: Linux Mastery

Module: Users and Groups

Lesson: 5 of 10

What You'll Learn¶

After completing this lesson, you'll be able to:

Understand environment variables
Differentiate shell variables and environment variables
View existing variables
Create environment variables
Export variables
Remove variables
Configure the PATH variable
Apply environment variables in production

Prerequisites¶

Complete:

Module 1 – Linux Fundamentals
Module 2 – Linux Command Line Essentials
Module 3 – Text Processing
Module 4 – File Management and Permissions
Module 5 Lessons 1–4

Why Learn Environment Variables?¶

Imagine you install Java.

Instead of running:

/usr/lib/jvm/java-21/bin/java

every time,

you simply run:

java

How does Linux know where Java is installed?

The answer is:

Environment Variables, especially the PATH variable.

What is an Environment Variable?¶

An environment variable is a name-value pair stored by the shell.

Example:

USER=basha

HOME=/home/basha

SHELL=/bin/bash

Applications use these values to determine how they should run.

Shell Variables vs Environment Variables¶

Shell Variable	Environment Variable
Available only in the current shell	Available to child processes
Not inherited	Inherited by child processes
Created with `VAR=value`	Exported using `export`

Viewing Environment Variables¶

Display all environment variables.

env

or

printenv

Example:

HOME=/home/basha

USER=basha

PATH=/usr/bin:/bin

SHELL=/bin/bash

Display a Specific Variable¶

Syntax:

echo $VARIABLE

Examples:

echo $USER

echo $HOME

echo $PATH

echo $SHELL

Common Environment Variables¶

Variable	Description
`USER`	Current username
`HOME`	User's home directory
`PATH`	Executable search path
`PWD`	Current directory
`OLDPWD`	Previous directory
`SHELL`	Current shell
`HOSTNAME`	System hostname
`LANG`	System language
`TERM`	Terminal type
`LOGNAME`	Login username

Creating a Shell Variable¶

CITY=Hyderabad

Verify:

echo $CITY

Output:

Hyderabad

This variable exists only in the current shell.

Exporting an Environment Variable¶

export CITY=Hyderabad

Verify:

printenv CITY

Output:

Hyderabad

Now child processes can access it.

Difference Between Shell and Environment Variables¶

Create a shell variable.

PROJECT=REBASH

Open a new shell.

bash

Check:

echo $PROJECT

Output:

The variable is not available.

Now export it.

export PROJECT=REBASH

Open another shell.

bash

Check again.

echo $PROJECT

Output:

REBASH

Removing Variables¶

unset PROJECT

Verify.

echo $PROJECT

Output:

Understanding PATH¶

Display:

echo $PATH

Example:

/usr/local/bin:/usr/bin:/bin:/usr/sbin

When you run:

python

Linux searches each directory in PATH until it finds the executable.

Adding a Directory to PATH¶

Temporarily:

export PATH=$PATH:/opt/tools/bin

Verify:

echo $PATH

Now executables inside /opt/tools/bin can be run without specifying the full path.

Environment Variables in Scripts¶

Example:

#!/bin/bash

echo "User: $USER"

echo "Home: $HOME"

echo "Shell: $SHELL"

Run:

bash info.sh

Listing Shell Variables¶

set

This displays:

Shell variables
Environment variables
Functions

Finding One Variable¶

printenv HOME

printenv PATH

Common Commands¶

Display all variables.

env

printenv

Display one variable.

echo $HOME

Create variable.

PROJECT=REBASH

Export variable.

export PROJECT=REBASH

Remove variable.

unset PROJECT

Display all shell variables.

set

Real Production Examples¶

Set Java Home.

export JAVA_HOME=/usr/lib/jvm/java-21

Configure Python.

export PYTHONPATH=/opt/python

Update PATH.

export PATH=$PATH:/opt/scripts

Configure Kubernetes.

export KUBECONFIG=~/.kube/config

Configure AWS CLI.

export AWS_PROFILE=production

Production Perspective¶

Environment variables are heavily used in:

Shell scripting
Docker containers
Kubernetes Pods
Jenkins pipelines
GitHub Actions
GitLab CI/CD
Python applications
Java applications
Node.js applications

Most modern applications read configuration from environment variables rather than hardcoded values.

Hands-on Lab¶

Task 1¶

Display all environment variables.

env

Task 2¶

Display your username.

echo $USER

Task 3¶

Display your home directory.

echo $HOME

Task 4¶

Display your PATH.

echo $PATH

Task 5¶

Create a variable.

PROJECT=REBASH

Display it.

echo $PROJECT

Task 6¶

Export the variable.

export PROJECT

Verify.

printenv PROJECT

Task 7¶

Remove the variable.

unset PROJECT

Task 8¶

List all shell variables.

set

Command Deep Dive¶

Command	Purpose	Production Example
`env`	Display environment variables	Troubleshooting
`printenv`	Display environment variables	Scripts
`echo $VAR`	Display variable value	Verification
`export`	Create environment variable	Application configuration
`unset`	Remove variable	Cleanup
`set`	Display shell variables	Debugging

Production Troubleshooting Scenario¶

Scenario

A Java application fails to start.

Error:

JAVA_HOME is not set

Investigation:

echo $JAVA_HOME

printenv JAVA_HOME

The variable is missing.

Solution:

export JAVA_HOME=/usr/lib/jvm/java-21

export PATH=$JAVA_HOME/bin:$PATH

Verify:

java -version

The application now starts successfully.

Best Practices¶

Use uppercase names for environment variables.
Keep variable names descriptive.
Avoid storing sensitive information (such as passwords or API keys) directly in environment variables on shared systems unless required and properly protected.
Use export only for variables that child processes need.
Configure permanent variables in profile files rather than setting them manually every session.

Common Mistakes¶

❌ Forgetting to export variables.

✅ Shell variables are not inherited by child processes.

❌ Overwriting the PATH variable.

✅ Incorrect:

export PATH=/opt/tools

Correct:

export PATH=$PATH:/opt/tools

❌ Hardcoding application paths in scripts instead of using environment variables.

✅ Prefer using environment variables rather than hardcoding application paths in scripts.

Interview Questions¶

Beginner¶

What is an environment variable?
Which command displays all environment variables?
What is the purpose of the PATH variable?
How do you display the value of an environment variable?

Intermediate¶

Explain the difference between shell variables and environment variables.
What does the export command do?
How do you add a directory to the PATH?
How do you remove an environment variable?

Architect Level¶

Why are environment variables widely used in cloud-native applications?
How do Docker and Kubernetes use environment variables?
What are the security considerations when storing configuration in environment variables?

Summary¶

In this lesson, you learned:

Environment variables
Shell variables
Viewing variables
Creating variables
Exporting variables
Removing variables
PATH
Production use cases

Environment variables are a core part of Linux and modern application deployment. They allow applications and scripts to be configured without changing source code, making them an essential tool for Linux administrators, DevOps engineers, and cloud architects.

Key Takeaways¶

Environment variables store configuration values used by the shell and applications.
Use env or printenv to display environment variables.
Use export to make variables available to child processes.
Use unset to remove variables.
The PATH variable determines where Linux searches for executable programs.
Environment variables are widely used in automation, containers, and cloud-native applications.

What's Next?¶

Linux Profiles — Configuring User Login Environments

You'll explore:

Login vs non-login shells
/etc/profile
~/.profile
~/.bash_profile
/etc/environment
Shell startup sequence
Configuring persistent environment settings

Understanding profile files will help you make environment variables and shell settings permanent across login sessions.