export command in Linux CLI - Commands & Configuration

Introduction

Sometimes you want to make a variable available to other programs or scripts you run from your shell. The export command lets you do this by marking variables so they can be used by child processes.

When you want a script to access a variable you set in your current shell session.

When you need to set environment variables like PATH or HOME for programs you start.

When you want to temporarily change a variable for a program you launch without changing it globally.

When you want to share configuration values between multiple commands run from the same shell.

When you want to make sure a variable is available to all scripts called from your shell.

Commands

This sets a variable named MY_VAR with the value 'hello' in the current shell session only.

Terminal

MY_VAR=hello

Expected Output

No output (command runs silently)

This prints the value of MY_VAR to confirm it is set in the current shell.

Terminal

echo $MY_VAR

Expected Output

hello

This marks MY_VAR to be exported, so any program or script started from this shell can access it.

Terminal

export MY_VAR

Expected Output

No output (command runs silently)

This runs a new shell and prints MY_VAR to show that the exported variable is available in child processes.

Terminal

bash -c 'echo $MY_VAR'

Expected Output

hello

Key Concept

If you remember nothing else from this pattern, remember: export makes a shell variable available to all programs started from that shell.

Common Mistakes

Setting a variable without export and expecting child processes to see it.

Variables set without export are only visible in the current shell, not in programs started from it.

Use export to mark variables you want child processes to access.

Using export without setting a variable first.

Exporting a variable that is not set does nothing useful and may cause confusion.

Set the variable first, then export it.

Summary

Set a variable in the shell using VAR=value.

Use export VAR to make the variable available to child processes.

Verify by running a child shell or program that prints the variable.

Practice

1. What does the export command do in a Linux shell?

easy

A. Makes a shell variable available to child processes

B. Deletes a shell variable permanently

C. Lists all files in the current directory

D. Changes the current directory

Solution

1. Step 1: Understand shell variables and environment

   Shell variables exist only in the current shell session unless exported.

2. Step 2: Role of export

   The export command marks a variable to be passed to child processes as environment variables.

3. Final Answer:

   Makes a shell variable available to child processes -> Option A

4. Quick Check:

   export = share variable with child processes [OK]

Hint: Export shares variables with child processes [OK]

Common Mistakes:

• Thinking export deletes variables
• Confusing export with file commands
• Assuming export changes directories

2. Which of the following is the correct syntax to export a variable named PATH with value /usr/local/bin?

easy

A. export =PATH /usr/local/bin

B. export PATH=/usr/local/bin

C. export PATH : /usr/local/bin

D. export PATH == /usr/local/bin

Solution

1. Step 1: Recall export syntax

   The correct syntax is export VARIABLE=VALUE without spaces around the equal sign.

2. Step 2: Check each option

   export PATH=/usr/local/bin matches the correct syntax. Others have invalid characters or spaces.

3. Final Answer:

   export PATH=/usr/local/bin -> Option B

4. Quick Check:

   export VAR=VALUE no spaces [OK]

Hint: No spaces around = in export syntax [OK]

Common Mistakes:

• Adding spaces around equal sign
• Using wrong symbols like : or ==
• Placing export after assignment

3. What will be the output of the following commands?

MYVAR="hello"
echo $MYVAR
export MYVAR
bash -c 'echo $MYVAR'

medium

A. \n\n

B. hello\n

C. \nhello

D. hello\nhello

Solution

1. Step 1: Understand variable assignment and export

   First, MYVAR is set to "hello" and printed, so first echo outputs "hello". Then MYVAR is exported.

2. Step 2: Child shell access

   The bash -c 'echo $MYVAR' runs a new shell which inherits exported variables, so it prints "hello" again.

3. Final Answer:

   hello hello -> Option D

4. Quick Check:

   Exported variable visible in child shell [OK]

Hint: Exported vars visible in child shells [OK]

Common Mistakes:

• Assuming unexported vars appear in child shells
• Confusing echo outputs with command prompts
• Ignoring export effect on subshells

4. Identify the error in this script snippet:

export MYVAR
MYVAR="world"
echo $MYVAR

medium

A. echo command is missing quotes

B. export command syntax is wrong

C. MYVAR is exported before assignment, so child shells get empty value

D. No error, script works fine

Solution

1. Step 1: Analyze export before assignment

   Exporting MYVAR before assigning means MYVAR is empty when exported.

2. Step 2: Effect on variable value

   Assigning MYVAR after export does not update the exported environment variable for child processes.

3. Final Answer:

   MYVAR is exported before assignment, so child shells get empty value -> Option C

4. Quick Check:

   Export before assignment exports empty value [OK]

Hint: Assign before export to share correct value [OK]

Common Mistakes:

• Exporting before assigning value
• Thinking export syntax is wrong
• Assuming echo needs quotes always

5. You want to set a variable CONFIG_PATH to /etc/config and ensure it is available to all scripts run from your current shell session and its children. Which sequence of commands achieves this correctly?

hard

A. CONFIG_PATH=/etc/config\nexport CONFIG_PATH

B. export CONFIG_PATH=/etc/config

C. export CONFIG_PATH\nCONFIG_PATH=/etc/config

D. CONFIG_PATH=/etc/config

Solution

1. Step 1: Assign variable before export

   Assigning CONFIG_PATH=/etc/config sets the value in the current shell.

2. Step 2: Export variable after assignment

   Running export CONFIG_PATH marks it for child processes with the assigned value.

3. Step 3: Check other options

   export CONFIG_PATH=/etc/config works but is less clear; export CONFIG_PATH\nCONFIG_PATH=/etc/config exports before assignment (wrong); CONFIG_PATH=/etc/config does not export.

4. Final Answer:

   CONFIG_PATH=/etc/config export CONFIG_PATH -> Option A

5. Quick Check:

   Assign then export to share variable [OK]

Hint: Assign first, then export to share variable [OK]

Common Mistakes:

• Exporting before assigning value
• Not exporting variable at all
• Assuming single export with assignment is always best