Environment variables in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an environment variable in Linux?

An environment variable is a named value stored by the operating system that programs can use to get information about the system or user settings. It acts like a note that programs can read to know how to behave.

beginner

How do you display all environment variables in a Linux shell?

You can use the command printenv or env to list all environment variables currently set in your shell session.

beginner

How do you set a new environment variable for the current shell session?

Use the command export NAME=value. For example, export MYVAR=hello sets an environment variable named MYVAR with the value 'hello' for the current session.

intermediate

What happens to environment variables when you close the terminal?

Environment variables set in a terminal session are lost when you close that terminal unless saved in configuration files like ~/.bashrc or ~/.profile to load automatically on new sessions.

beginner

How can you use an environment variable inside a shell script?

You can access an environment variable in a shell script by prefixing its name with a dollar sign, like $VARIABLE_NAME. For example, echo $HOME prints the home directory path.

Which command shows all environment variables in Linux?

A mkdir

B ls

C cd

D printenv

The printenv command lists all environment variables. Other commands like ls, cd, and mkdir do not show environment variables.

How do you set an environment variable named PATH to '/usr/bin' for the current session?

A export PATH=/usr/bin

B set PATH=/usr/bin

C PATH=/usr/bin

D env PATH=/usr/bin

Use export PATH=/usr/bin to set and export the variable so child processes can see it. Just PATH=/usr/bin sets it only for the current shell, not exported.

What symbol do you use to access the value of an environment variable in a shell script?

A #

B $

C &

D *

The dollar sign $ is used to access the value of an environment variable, e.g., $HOME.

Where should you save environment variable settings to make them permanent for your user?

A /tmp

B /etc/passwd

C ~/.bashrc

D /var/log

User-specific environment variables are often saved in ~/.bashrc or ~/.profile to load automatically on new shell sessions.

If you set an environment variable in one terminal, will it be available in a new terminal window automatically?

A No, unless saved in config files

B Only if you reboot

C Yes, always

D Only if you use sudo

Environment variables set in one terminal session are not available in new terminals unless saved in configuration files like ~/.bashrc.

Explain what environment variables are and how they are used in Linux.

Think about how programs know about your system or preferences.

Describe the steps to create a new environment variable that lasts across terminal sessions.

Consider both temporary and permanent ways.

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