Environment variables in Linux CLI - Commands & Configuration

Introduction

Environment variables store information that programs and scripts use to work properly. They help keep settings like paths and user preferences outside the code, making it easier to change behavior without editing scripts.

When you want to set a temporary value for a program to use during its run.

When you need to share configuration settings like database addresses or API keys across multiple scripts.

When you want to check what settings or paths are currently active in your shell.

When you want to make a variable available to all programs started from your shell.

When you want to customize your command prompt or other shell behaviors.

Commands

This command sets an environment variable named MY_VAR with the value HelloWorld and makes it available to all child processes started from this shell.

Terminal

export MY_VAR="HelloWorld"

Expected Output

No output (command runs silently)

This command prints the value of the environment variable MY_VAR to the terminal, showing what is currently stored.

Terminal

echo $MY_VAR

Expected Output

HelloWorld

This command lists all environment variables and filters the output to show only the variable MY_VAR, confirming it is set.

Terminal

env | grep MY_VAR

Expected Output

MY_VAR=HelloWorld

→

| grep MY_VAR - Filters the list to show only lines containing MY_VAR

This command removes the environment variable MY_VAR from the current shell session, so it is no longer available.

Terminal

unset MY_VAR

Expected Output

No output (command runs silently)

After unsetting, this command tries to print MY_VAR again, showing that it no longer has a value.

Terminal

echo $MY_VAR

Key Concept

If you remember nothing else from this pattern, remember: environment variables store settings outside your scripts so you can change behavior without editing code.

Common Mistakes

Setting a variable without export, like MY_VAR="HelloWorld"

The variable is only available in the current shell and not to programs or scripts started from it.

Use export MY_VAR="HelloWorld" to make it available to child processes.

Trying to access a variable without the $ sign, like echo MY_VAR

This prints the literal text MY_VAR instead of the variable's value.

Use echo $MY_VAR to print the value stored in the variable.

Expecting environment variables to persist after closing the terminal.

Variables set in a shell session are lost when the session ends.

Add export commands to shell startup files like ~/.bashrc to make them permanent.

Summary

Use export to create environment variables accessible to programs and scripts.

Use echo with $ to see the value of an environment variable.

Use unset to remove an environment variable from the current session.

Practice

1. What is the purpose of environment variables in a Linux shell?

easy

A. To speed up the internet connection

B. To store settings that programs can use during execution

C. To permanently delete files from the system

D. To create new user accounts automatically

Solution

1. Step 1: Understand environment variables

   Environment variables hold information like settings or preferences that programs can read while running.

2. Step 2: Identify the correct purpose

   Among the options, only storing settings matches the role of environment variables.

3. Final Answer:

   To store settings that programs can use during execution -> Option B

4. Quick Check:

   Environment variables = store settings [OK]

Hint: Remember: environment variables hold settings, not files or users [OK]

Common Mistakes:

• Confusing environment variables with file operations
• Thinking environment variables control hardware
• Assuming environment variables create users

2. Which command correctly sets an environment variable named MY_VAR with value hello for the current shell and its child processes?

easy

A. declare MY_VAR hello

B. set MY_VAR=hello

C. env MY_VAR hello

D. export MY_VAR=hello

Solution

1. Step 1: Recall how to set environment variables

   In Linux shells, export is used to set environment variables for the current shell and its children.

2. Step 2: Check each command

   set MY_VAR=hello is incorrect syntax; env MY_VAR hello does not set variable persistently; declare MY_VAR hello is invalid for environment variables.

3. Final Answer:

   export MY_VAR=hello -> Option D

4. Quick Check:

   Use export to set environment variables [OK]

Hint: Use 'export' to set environment variables for shell and children [OK]

Common Mistakes:

• Using 'set' instead of 'export' to set environment variables
• Trying to set variables without export, so children don't see them
• Confusing 'env' command usage

3. Given the commands below, what will be the output of echo $GREETING?

GREETING="Hello"
export GREETING
GREETING="Hi"
echo $GREETING

medium

A. Hello

B. $GREETING

C. Hi

D. Error: variable not found

Solution

1. Step 1: Understand variable assignment and export

   First, GREETING is set to "Hello" and exported, making it available to child processes. Then GREETING is reassigned to "Hi" in the current shell.

2. Step 2: Determine the value echoed

   The echo command prints the current value of GREETING, which is "Hi" after reassignment.

3. Final Answer:

   Hi -> Option C

4. Quick Check:

   Variable reassignment updates value = Hi [OK]

Hint: Last assignment before echo is the value printed [OK]

Common Mistakes:

• Thinking export freezes the variable value
• Expecting the first assigned value to print
• Confusing export with immediate output

4. What is wrong with this script snippet if the goal is to set PATH to include /usr/local/bin?

PATH=$PATH:/usr/local/bin
export PATH

medium

A. Nothing is wrong; it correctly appends to PATH

B. It should use export PATH=$PATH:/usr/local/bin in one line

C. It overwrites PATH instead of appending

D. It should prepend /usr/local/bin before $PATH

Solution

1. Step 1: Analyze the PATH modification

   The script appends :/usr/local/bin to the existing PATH variable, which is a common way to add directories.

2. Step 2: Check export usage

   Exporting PATH after assignment makes the new value available to child processes. This is correct usage.

3. Final Answer:

   Nothing is wrong; it correctly appends to PATH -> Option A

4. Quick Check:

   Appending and exporting PATH is correct [OK]

Hint: Appending PATH then exporting is standard practice [OK]

Common Mistakes:

• Thinking export must be on same line as assignment
• Confusing append with overwrite
• Assuming order of PATH parts always matters

5. You want to create a script that sets a temporary environment variable TEMP_VAR only for a single command execution, without affecting the shell's environment afterwards. Which command correctly does this?

hard

A. TEMP_VAR=value command

B. export TEMP_VAR=value; command

C. set TEMP_VAR=value command

D. command; export TEMP_VAR=value

Solution

1. Step 1: Understand temporary environment variables for one command

   Setting a variable before a command like TEMP_VAR=value command runs the command with that variable set only for its execution.

2. Step 2: Evaluate each option

   export TEMP_VAR=value; command exports variable globally; set TEMP_VAR=value command uses invalid syntax; command; export TEMP_VAR=value sets variable after command runs.

3. Final Answer:

   TEMP_VAR=value command -> Option A

4. Quick Check:

   Prefix variable before command for temporary env [OK]

Hint: Put variable before command to set it temporarily [OK]

Common Mistakes:

• Using export which affects shell permanently
• Trying to set variable after command runs
• Using incorrect syntax like 'set' for env variables