export command in Linux CLI - Step-by-Step Execution

Concept Flow - export command

Start shell session

↓

Define variable

↓

Use export command

↓

Variable added to environment

↓

Child processes inherit variable

↓

End

The export command marks a shell variable to be passed to child processes, making it part of the environment.

Execution Sample

Linux CLI

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

Defines a variable, exports it, then runs a child shell that prints the variable's value.

Execution Table

Step	Action	Variable State	Output
1	Define MYVAR=hello	MYVAR=hello (shell only)
2	Run export MYVAR	MYVAR=hello (environment)
3	Run child shell: bash -c 'echo $MYVAR'	Child shell inherits MYVAR=hello	hello
4	End	No change

💡 Child shell prints 'hello' because MYVAR was exported to environment.

Variable Tracker

Variable	Start	After export	In child shell
MYVAR	undefined	hello (exported)	hello

Key Moments - 2 Insights

Why does the child shell print 'hello' only after export?

Because before export, MYVAR is only a shell variable, not in the environment. Export adds it to the environment so child shells can see it, as shown in execution_table step 3.

What happens if you define a variable but do not export it?

The variable stays local to the current shell and is not visible to child processes, so commands like 'bash -c' won't see it (see execution_table step 1 vs 3).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of MYVAR in the child shell?

A hello

B undefined

C empty string

D MYVAR

💡 Hint

Check execution_table row 3 under Output and Variable State columns.

At which step does MYVAR become part of the environment?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at execution_table step 2 where export is run.

If you remove the export command, what will the child shell output be?

A hello

B MYVAR

C empty string

D error

💡 Hint

Refer to key_moments about variable visibility without export.

Concept Snapshot

export command:
- Marks a shell variable for environment export
- Makes variable visible to child processes
- Syntax: export VAR_NAME
- Without export, variable is local to current shell
- Useful for passing config to scripts or subshells

Full Transcript

The export command in Linux shell is used to make a variable part of the environment. When you define a variable like MYVAR=hello, it exists only in the current shell. Running export MYVAR adds it to the environment so child processes, like a new bash shell, can access it. This is why the child shell prints 'hello' when running 'bash -c echo $MYVAR'. Without export, the child shell would not see the variable and print nothing. Export is essential for passing variables to scripts or subshells.

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