Bash Trap Ctrl+C (SIGINT) | Handle Signals with Examples

Bash Trap Ctrl+C

Capture Ctrl+C (SIGINT) Example

Here is a simple while loop to demonstrate the behavior:

#!/bin/bash

trap 'echo "Ctrl+C detected. Exiting..."; exit' INT

echo "Press Ctrl+C to test"
while true; do
    sleep 1
done

Explanation

• INT represents the Ctrl+C signal (SIGINT)
• When Ctrl+C is pressed, the trap command executes the defined action
• Instead of exiting immediately, the script runs custom logic

Common Signals (INT, TERM, EXIT)

Example using multiple signals:

trap 'echo "Cleanup before exit"; rm -f /tmp/testfile' INT TERM EXIT

Tip

• Use INT to capture Ctrl+C
• Use TERM for graceful shutdown
• Use EXIT for cleanup tasks

What is Ctrl+C Signal in Linux

What Signal Ctrl+C Sends (SIGINT)

Ctrl+C sends the SIGINT (Signal Interrupt) to the process.

$ trap -l | grep INT
2) SIGINT

Explanation

• SIGINT is signal number 2
• It tells the program to stop execution
• By default, most programs terminate immediately when SIGINT is received

Example

sleep 100

Pressing Ctrl+C will terminate the command instantly.

Signal Numbers and Names

Linux supports many signals that can be sent to processes.

List all signals:

trap -l

Common signals:

Tip

• Use signal names (SIGINT) instead of numbers for readability
• Some signals like SIGKILL cannot be trapped

Bash Trap Command (Syntax & Basics)

Basic Trap Syntax

trap 'commands' SIGNAL

Example

trap 'echo "Interrupted!"; exit' INT

Explanation

• Executes the command when SIGINT (Ctrl+C) is received
• Prevents abrupt script termination
• Useful for cleanup and logging

Trap Multiple Signals Example

You can handle multiple signals in a single trap command.

trap 'echo "Cleaning up..."; rm -f /tmp/file' INT TERM EXIT

Explanation

• INT → Ctrl+C
• TERM → graceful termination
• EXIT → runs when script exits

Use case

• Remove temporary files
• Close connections
• Perform cleanup before exit

Capture Ctrl+C in Bash Script

Simple Ctrl+C Trap Example

This example captures Ctrl+C (SIGINT) and executes a custom message before exiting.

#!/bin/bash

trap 'echo "Ctrl+C detected. Exiting safely..."; exit' INT

echo "Running script. Press Ctrl+C to stop."

while true; do
    sleep 1
done

Explanation

• INT represents Ctrl+C
• Instead of immediate termination, the trap executes custom logic
• Useful for graceful exits

Trap Ctrl+C with Cleanup Function

A better approach is to define a function and call it when the signal is received.

#!/bin/bash

cleanup() {
    echo "Cleaning up resources..."
    rm -f /tmp/testfile
    exit
}

trap cleanup INT

touch /tmp/testfile

while true; do
    echo "Script running..."
    sleep 2
done

Explanation

• Cleanup logic is separated into a function
• Improves readability and reusability
• Ensures temporary files are removed before exit

Bash Trap Real-World Use Cases

Cleanup Temporary Files on Exit

This example ensures that temporary or log files are automatically removed when the script exits, whether normally or due to interruption.

trap 'rm -f /tmp/app.log; echo "Logs cleaned"' EXIT

Handle Interrupted Script Safely

This example captures Ctrl+C (SIGINT) and performs a safe exit by executing custom logic such as saving progress or displaying a message.

trap 'echo "Process interrupted. Saving state..."; exit' INT

Prevent Script Termination (Ignore Ctrl+C)

This example ignores the Ctrl+C signal completely, allowing the script to continue running without interruption.

trap '' INT

Explanation

• Ignores Ctrl+C completely
• Script continues running

Advanced Trap Usage

Trap Multiple Signals (INT, TERM, EXIT)

trap 'echo "Cleaning up before exit"; rm -f /tmp/file' INT TERM EXIT

Explanation

• Handles multiple signals in one place
• Ensures cleanup happens in all exit scenarios

Reset Trap to Default Behavior

trap - INT

Explanation

• Removes custom trap
• Restores default behavior (Ctrl+C will terminate script)

Ignore Signals in Bash Script

trap '' TERM

Explanation

• Ignores SIGTERM signal
• Useful for protecting critical processes

Tip

• Do not ignore signals blindly in production
• Always ensure safe exit mechanisms are available

Common Mistakes and Fixes

Trap Not Working (Wrong Quotes)

Using incorrect quotes can cause the trap command to behave unexpectedly.

Problem

trap "echo $var" INT

• Variables are expanded immediately when trap is set
• Not when the signal is received

Fix

trap 'echo $var' INT

Explanation

• Single quotes delay variable expansion
• Ensures the command runs correctly when the signal occurs

Script Still Exits on Ctrl+C

Sometimes the script exits even after defining a trap.

Possible causes

• exit is explicitly called inside the trap
• Signal is not handled properly
• Script receives another signal (like SIGTERM)

Fix

trap 'echo "Ctrl+C captured";' INT

Explanation

• Avoid using exit unless required
• Ensure trap handles only intended signals

Trap Not Triggered in Subshell

Traps may not work as expected inside subshells or child processes.

Problem

( trap 'echo "Ctrl+C captured"' INT; sleep 10 )

• Subshell has its own signal handling
• Parent trap may not apply

Fix

trap 'echo "Ctrl+C captured"' INT

sleep 10

Explanation

• Define traps in the main shell context
• Avoid relying on subshells for signal handling

Summary

• Ctrl+C sends SIGINT (signal 2) to running processes
• Bash trap allows handling signals gracefully
• Use traps to perform cleanup, logging, or safe exit
• Prefer functions for complex trap logic
• Avoid deep nesting and improper signal handling
• Always test traps with real interruptions

Official Documentation

• Bash Signals Documentation
• Bash trap Command Reference
• Linux Signal Documentation