trap for cleanup on exit in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run the cleanup function when the script exits.

Bash Scripting

trap [1] EXIT

cleanup() {
  echo "Cleaning up..."
}

cleanup

Drag options to blanks, or click blank then click option'

Asignal

Bexit

Ctrap

Dcleanup

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'exit' instead of the function name in trap.

Adding parentheses after the function name in trap.

Using 'signal' which is not a command here.

The trap command runs the specified function or command when the script receives the EXIT signal. Here, 'cleanup' is the function to run.

2fill in blank

medium

Complete the code to trap both EXIT and INT signals to run cleanup.

Bash Scripting

trap [1] EXIT INT

cleanup() {
  echo "Cleaning up resources..."
}

cleanup

Drag options to blanks, or click blank then click option'

AINT

Bcleanup()

Ccleanup

Dexit

Attempts:

3 left

💡 Hint

Common Mistakes

Including parentheses after the function name in trap.

Using signal names as the command to run.

Forgetting to list all signals after the command.

The trap command takes the function name without parentheses to run on specified signals like EXIT and INT (Ctrl+C).

3fill in blank

hard

Fix the error in the trap command to correctly call cleanup on script exit.

Bash Scripting

trap [1] EXIT

cleanup() {
  echo "Done cleaning."
}

cleanup

Drag options to blanks, or click blank then click option'

Acleanup()

Bcleanup

C"cleanup"

D'cleanup()'

Attempts:

3 left

💡 Hint

Common Mistakes

Adding parentheses after the function name in trap.

Using quotes around the function name.

Using the wrong command name.

In trap, the function name should be given without parentheses or quotes to run correctly on exit.

4fill in blank

hard

Fill both blanks to create a trap that runs cleanup on EXIT and TERM signals.

Bash Scripting

trap [1] [2]

cleanup() {
  echo "Cleanup done."
}

cleanup

Drag options to blanks, or click blank then click option'

Acleanup

BEXIT

CTERM

DB C

Attempts:

3 left

💡 Hint

Common Mistakes

Putting signals before the command.

Using wrong signal names.

Adding parentheses to the function name.

The trap command syntax is: trap command signals. Here, 'cleanup' is the command, and 'EXIT TERM' are the signals.

5fill in blank

hard

Fill all three blanks to trap cleanup on EXIT and INT signals and define the cleanup function.

Bash Scripting

trap [1] [2]

[3]() {
  echo "Exiting and cleaning up."
}

cleanup

Drag options to blanks, or click blank then click option'

Acleanup

BEXIT INT

Dexit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'exit' instead of 'cleanup' as the function name.

Not listing both signals.

Adding parentheses to the function name.

The trap command runs 'cleanup' on signals 'EXIT INT'. The function named 'cleanup' is defined to run the cleanup code.

Practice

1. What is the main purpose of using trap in a bash script?

easy

A. To define functions inside the script

B. To create loops that repeat commands

C. To run specific commands when the script exits or receives signals

D. To declare variables with default values

Solution

1. Step 1: Understand the role of trap

   The trap command is designed to catch signals or script exit events and run commands in response.

2. Step 2: Compare options with trap's purpose

   Options B, C, and D describe other bash features unrelated to trap. Only To run specific commands when the script exits or receives signals correctly describes its purpose.

3. Final Answer:

   To run specific commands when the script exits or receives signals -> Option C

4. Quick Check:

   trap runs commands on exit/signals = A [OK]

Hint: Trap runs cleanup commands on exit or signals [OK]

Common Mistakes:

• Confusing trap with loops or functions
• Thinking trap declares variables
• Assuming trap runs commands continuously

2. Which of the following is the correct syntax to run cleanup function on script exit using trap?

easy

A. trap EXIT cleanup

B. trap 'cleanup' on EXIT

C. trap cleanup on EXIT

D. trap 'cleanup' EXIT

Solution

1. Step 1: Recall trap syntax for commands

   The command(s) to run must be quoted as a string, followed by the signal or event name.

2. Step 2: Check each option's syntax

   trap 'cleanup' EXIT correctly quotes the command and uses the signal EXIT. trap EXIT cleanup places the signal before the command (wrong order). Options C and D use incorrect keywords like 'on'.

3. Final Answer:

   trap 'cleanup' EXIT -> Option D

4. Quick Check:

   trap 'command' SIGNAL = B [OK]

Hint: Always quote commands in trap before the signal [OK]

Common Mistakes:

• Omitting quotes around commands
• Using 'on' keyword incorrectly
• Placing signal before command

3. What will be the output of this script?

#!/bin/bash
cleanup() {
  echo "Cleaning up temp files"
}
trap 'cleanup' EXIT

echo "Script is running"

medium

A. Script is running

B. Script is running\nCleaning up temp files

C. No output

D. Cleaning up temp files

Solution

1. Step 1: Understand script flow

   The script prints "Script is running" first, then exits.

2. Step 2: Effect of trap on EXIT

   On exit, the cleanup function runs, printing "Cleaning up temp files" after the first echo.

3. Final Answer:

   Script is running\nCleaning up temp files -> Option B

4. Quick Check:

   trap runs cleanup on exit, so both lines print [OK]

Hint: trap runs cleanup after script finishes [OK]

Common Mistakes:

• Thinking trap runs before script output
• Expecting only cleanup message
• Ignoring trap on EXIT

4. Identify the error in this script snippet that uses trap for cleanup:

#!/bin/bash
trap cleanup EXIT

cleanup() {
  echo "Cleaning up"
}

medium

A. No error, script is correct

B. EXIT signal is invalid

C. trap command missing quotes around cleanup

D. cleanup function is defined after trap command

Solution

1. Step 1: Check trap command syntax

   For simple function names like cleanup, quotes are not required around the command in trap.

2. Step 2: Analyze script order and signals

   Defining cleanup after trap is allowed because bash processes function definitions before executing traps. EXIT is valid. No syntax errors present.

3. Final Answer:

   No error, script is correct -> Option A

4. Quick Check:

   unquoted function name OK, post-definition OK [OK]

Hint: trap accepts unquoted simple function names [OK]

Common Mistakes:

• Thinking functions must be defined before trap
• Believing EXIT is an invalid signal
• Assuming quotes are required around simple commands

5. You want to ensure a temporary file /tmp/mytempfile is deleted when your bash script exits, even if interrupted. Which trap command correctly achieves this?

hard

A. trap 'rm -f /tmp/mytempfile' EXIT INT TERM

B. trap rm -f /tmp/mytempfile EXIT INT TERM

C. trap 'rm -f /tmp/mytempfile' ONEXIT

D. trap 'rm -f /tmp/mytempfile' EXIT SIGNAL

Solution

1. Step 1: Understand trap for multiple signals

   To catch script exit and interruptions, use signals EXIT, INT, and TERM together.

2. Step 2: Check syntax correctness

   Commands must be quoted. trap 'rm -f /tmp/mytempfile' EXIT INT TERM quotes the command and lists valid signals. Options B misses quotes, C uses invalid signal ONEXIT, D uses invalid SIGNAL keyword.

3. Final Answer:

   trap 'rm -f /tmp/mytempfile' EXIT INT TERM -> Option A

4. Quick Check:

   trap 'command' SIGNALS with quotes = A [OK]

Hint: Quote commands and list all signals to catch [OK]

Common Mistakes:

• Missing quotes around commands
• Using invalid signal names
• Not including INT and TERM for interrupts