Environment variables vs local variables in Bash Scripting - Practice Questions

Challenge - 5 Problems

💻 Command Output

intermediate

Output of local vs environment variable in subshell

What is the output of this script?

MYVAR="hello"
(export MYVAR; (echo $MYVAR))
echo $MYVAR

Bash Scripting

MYVAR="hello"
(export MYVAR; (echo $MYVAR))
echo $MYVAR

A hello\n

B \nhello

C hello\nhello

D \n

💡 Hint

Remember that exporting a variable makes it available to subshells.

The variable MYVAR is set locally and then exported, so the subshell can access it and print 'hello'. The final echo prints the local MYVAR which is still 'hello'.

💻 Command Output

intermediate

Effect of local variable inside function on environment

What is the output of this script?

MYVAR="start"
myfunc() {
  local MYVAR="inside"
  echo $MYVAR
}
myfunc
echo $MYVAR

Bash Scripting

MYVAR="start"
myfunc() {
  local MYVAR="inside"
  echo $MYVAR
}
myfunc
echo $MYVAR

A start\ninside

B inside\ninside

C start\nstart

D inside\nstart

💡 Hint

Local variables inside functions do not affect variables outside.

The function defines a local MYVAR which shadows the global one. Inside the function, it prints 'inside'. Outside, the original MYVAR remains 'start'.

🔧 Debug

advanced

Why environment variable is not updated in parent shell?

Consider this script:

export MYVAR="old"
(change_var() {
  MYVAR="new"
  export MYVAR
})
(change_var)
echo $MYVAR

Why does the echo print 'old' instead of 'new'?

Bash Scripting

export MYVAR="old"
(change_var() {
  MYVAR="new"
  export MYVAR
})
(change_var)
echo $MYVAR

A Because the function runs in a subshell, changes do not affect the parent shell

B Because export does not update existing environment variables

C Because MYVAR is local by default inside functions

D Because the variable was not declared with local keyword

💡 Hint

Think about where the function runs and how environment variables propagate.

The function runs inside parentheses, which creates a subshell. Changes to variables in a subshell do not affect the parent shell environment.

🧠 Conceptual

advanced

Difference between local and environment variables

Which statement correctly describes the difference between local and environment variables in bash?

A Local variables exist only within the current shell or function, environment variables are inherited by child processes

B Environment variables exist only within the current shell, local variables are inherited by child processes

C Local variables are automatically exported to child processes, environment variables are not

D Environment variables are temporary, local variables are permanent

💡 Hint

Think about variable visibility and inheritance.

Local variables are limited to the current shell or function scope. Environment variables are exported and passed to child processes.

🚀 Application

expert

Preserving environment variable changes after script execution

You have a script that sets and exports an environment variable MYVAR. After running the script normally, the variable is not set in your current shell. How can you modify your usage to have MYVAR set in your current shell after running the script?

A Run the script normally: ./script.sh

B Run the script with the source command: source ./script.sh

C Run the script in a new terminal window

D Add local MYVAR in the script before exporting

💡 Hint

Think about how environment variables propagate between shells.

Running the script with source executes it in the current shell, so environment variable changes persist after the script finishes.

Practice

1. What is the main difference between an environment variable and a local variable in a Bash script?

easy

A. Local variables are available to child processes, environment variables are not.

B. Environment variables are available to child processes, local variables are not.

C. Environment variables can only be numbers, local variables can be strings.

D. Local variables are global, environment variables are only inside functions.

Solution

1. Step 1: Understand environment variables

   Environment variables are set with export and are inherited by child processes.

2. Step 2: Understand local variables

   Local variables exist only in the current shell or function and are not passed to child processes.

3. Final Answer:

   Environment variables are available to child processes, local variables are not. -> Option B

4. Quick Check:

   Environment = exported, local = not exported [OK]

Hint: Remember: export makes variables visible to child processes [OK]

Common Mistakes:

• Thinking local variables are inherited by child processes
• Confusing export with local keyword
• Assuming environment variables are only inside functions

2. Which of the following is the correct way to create a local variable inside a Bash function?

easy

A. VAR=value

B. export VAR=value

C. local VAR=value

D. setlocal VAR=value

Solution

1. Step 1: Identify local variable syntax in Bash functions

   Inside a function, the keyword local declares a variable limited to that function.

2. Step 2: Compare options

   export makes variables environment variables, setlocal is not a Bash command, and VAR=value without local is global or inherited.

3. Final Answer:

   local VAR=value -> Option C

4. Quick Check:

   Use local inside functions for local variables [OK]

Hint: Use 'local' keyword inside functions for local variables [OK]

Common Mistakes:

• Using export instead of local inside functions
• Assuming VAR=value inside function is local
• Using non-existent commands like setlocal

3. What will be the output of this script?

VAR=hello
function test_func() {
  local VAR=world
  echo $VAR
}
test_func
echo $VAR

medium

A. world
hello

B. hello
hello

C. world
world

D. hello
world

Solution

1. Step 1: Analyze variable inside function

   The function declares a local variable VAR with value 'world', so echo $VAR inside prints 'world'.

2. Step 2: Analyze variable outside function

   The global VAR remains 'hello', so echo $VAR after function call prints 'hello'.

3. Final Answer:

   world hello -> Option A

4. Quick Check:

   Local inside function, global outside [OK]

Hint: Local variables override global only inside functions [OK]

Common Mistakes:

• Assuming local variable changes global variable
• Confusing output order
• Ignoring local keyword effect

4. Identify the error in this script snippet:

export VAR=hello
function test() {
  VAR=world
  local VAR
  echo $VAR
}
test
echo $VAR

medium

A. local must be declared before assigning VAR inside function

B. export cannot be used outside functions

C. echo $VAR inside function will print empty

D. Function syntax is incorrect

Solution

1. Step 1: Understand local variable declaration order

   In Bash, local VAR must appear before assigning a value to VAR inside the function to make it local.

2. Step 2: Analyze the script behavior

   Here, VAR=world assigns to global VAR before local VAR is declared, so local VAR is empty and echo $VAR prints empty.

3. Final Answer:

   local must be declared before assigning VAR inside function -> Option A

4. Quick Check:

   Declare local before assignment inside functions [OK]

Hint: Declare local variables before assigning values inside functions [OK]

Common Mistakes:

• Assigning before declaring local causes unexpected behavior
• Thinking export is invalid outside functions
• Assuming function syntax is wrong

5. You want to write a Bash script that sets a variable PATH_VAR inside a function and have it available outside the function and in any child processes. Which is the correct approach?

hard

A. Inside the function, use export PATH_VAR=value after declaring local PATH_VAR.

B. Declare local PATH_VAR=value inside the function and then export PATH_VAR outside the function.

C. Use local PATH_VAR=value inside the function and do nothing else.

D. Assign PATH_VAR=value inside the function and then export PATH_VAR inside the function without local.

Solution

1. Step 1: Understand local vs exported variables

   Declaring a variable as local limits it to the function scope, so it won't be available outside or to child processes.

2. Step 2: Correct way to export variable from function

   Assign the variable without local inside the function, then use export PATH_VAR inside the function to make it environment variable accessible outside and to child processes.

3. Final Answer:

   Assign PATH_VAR=value inside the function and then export PATH_VAR inside the function without local. -> Option D

4. Quick Check:

   Export without local to share variable outside function [OK]

Hint: Don't use local if you want variable exported outside function [OK]

Common Mistakes:

• Using local and export together inside function
• Exporting variable only outside function after local declaration
• Assuming local variables can be exported