Signal handling with trap in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the trap command in bash scripting?

The trap command lets a script catch signals (like Ctrl+C) and run specific commands before exiting or continuing. It helps scripts handle interruptions safely.

beginner

How do you use trap to run a cleanup function when the script receives a SIGINT (Ctrl+C)?

You write: trap cleanup_function SIGINT. This means when the script gets SIGINT, it runs cleanup_function before stopping.

beginner

What happens if you don’t use trap and press Ctrl+C during a bash script?

The script stops immediately without running any cleanup. This might leave temporary files or processes running.

intermediate

Explain the syntax of the trap command.

The syntax is: trap 'commands' SIGNALS. You put the commands to run in quotes, then list one or more signals to catch.

intermediate

Can trap handle multiple signals at once? How?

Yes. You list multiple signals after the commands, like: trap 'echo Signal caught' SIGINT SIGTERM. The commands run if any listed signal occurs.

What does the trap command do in a bash script?

A Catches signals and runs commands before exiting

B Starts a new background process

C Creates a new file

D Changes file permissions

The trap command catches signals like Ctrl+C and runs specified commands before the script exits or continues.

Which signal is sent when you press Ctrl+C in the terminal?

A SIGINT

B SIGKILL

C SIGHUP

D SIGTERM

Ctrl+C sends the SIGINT (interrupt) signal to the running process.

How do you remove a previously set trap in bash?

A trap - SIGNAL

B trap '' SIGNAL

C trap reset SIGNAL

D trap clear SIGNAL

Using trap '' SIGNAL removes the trap for that signal.

What will this command do? trap 'echo Exiting' EXIT

A Print 'Exiting' when Ctrl+C is pressed

B Restart the script

C Ignore all signals

D Print 'Exiting' when the script ends

The EXIT signal runs when the script finishes, so it prints 'Exiting' at the end.

If a script traps SIGTERM and SIGINT with the same command, what happens when either signal is received?

A The command runs only for SIGINT

B The command runs only for SIGTERM

C The command runs for both signals

D The script ignores both signals

The trap command runs the specified commands for any of the listed signals.

Describe how to use the trap command to handle a signal and why it is useful in bash scripts.

Think about what happens when you press Ctrl+C and how trap can help.

Explain what happens if a bash script does not use trap and receives an interrupt signal.

Consider what happens when you stop a program suddenly.