trap for cleanup on exit in Bash Scripting - Step-by-Step Execution

Concept Flow - trap for cleanup on exit

Start Script

↓

Set trap for EXIT

↓

Run main commands

↓

Script ends or interrupted

↓

Trap triggers cleanup function

↓

Cleanup actions run

↓

Exit script

The script sets a trap to run cleanup code when it exits normally or is interrupted.

Execution Sample

Bash Scripting

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

echo "Script running"

This script sets a trap to run the cleanup function when the script exits.

Execution Table

Step	Action	Output	Trap Triggered	Notes
1	Define cleanup function		No	Function ready but not run
2	Set trap on EXIT to cleanup		No	Trap set for script exit
3	Print 'Script running'	Script running	No	Main script running
4	Script ends normally		Yes	Trap triggers cleanup
5	Run cleanup function	Cleaning up...	Yes	Cleanup runs on exit

💡 Script ends, trap on EXIT triggers cleanup function

Variable Tracker

Variable	Start	After Step 3	After Step 5
cleanup function	Defined	Defined	Executed

Key Moments - 2 Insights

Why does the cleanup function run even though we never call it explicitly?

Because the trap command links the cleanup function to the EXIT signal, so it runs automatically when the script ends (see execution_table step 4 and 5).

What happens if the script is interrupted with Ctrl+C?

The EXIT trap still triggers the cleanup function, ensuring cleanup runs on interruption as well.

Visual Quiz - 3 Questions

Look at the execution table, what is printed at step 3?

A Nothing

B "Cleaning up..."

C "Script running"

D "Exit script"

💡 Hint

Check the Output column at step 3 in the execution_table.

At which step does the cleanup function run?

A Step 2

B Step 5

C Step 3

D Step 1

💡 Hint

Look at the Trap Triggered and Output columns in the execution_table.

If we remove the trap command, what changes in the execution?

A Cleanup function never runs unless called explicitly

B Cleanup function runs automatically on exit

C Script prints "Cleaning up..." before "Script running"

D Script will not print anything

💡 Hint

Refer to the role of trap in linking cleanup to script exit in the concept_flow.

Concept Snapshot

trap command links signals to functions
Use 'trap cleanup EXIT' to run cleanup on script exit
Cleanup runs on normal exit or interruption
Ensures resources are freed or temp files removed
No explicit call needed for cleanup function

Full Transcript

This script defines a cleanup function and sets a trap to run it when the script exits. The trap command listens for the EXIT signal, which happens when the script finishes or is interrupted. When the script runs, it prints 'Script running'. When the script ends, the trap triggers the cleanup function, which prints 'Cleaning up...'. This ensures cleanup code always runs without needing explicit calls.