Signal handling with trap in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output when SIGINT is sent?

Consider this bash script that traps SIGINT (Ctrl+C) and prints a message before exiting. What will be printed if the user presses Ctrl+C while the script is running?

Bash Scripting

trap 'echo "Caught SIGINT, exiting..."; exit 1' SIGINT
while true; do
  echo "Running..."
  sleep 1
done

A Running...\nRunning...\nCaught SIGINT, exiting...

B Running...\nRunning...\nTerminated

C Caught SIGINT, exiting...

D Running...\nRunning...\nRunning... (script never stops)

💡 Hint

Think about what the trap command does when SIGINT is received.

The trap command catches the SIGINT signal and runs the echo and exit commands. So the script prints 'Running...' repeatedly until Ctrl+C is pressed, then prints the message and exits.

💻 Command Output

intermediate

What happens if trap is not set for SIGTERM?

Given this script, what will happen if it receives a SIGTERM signal?

Bash Scripting

while true; do
  echo "Waiting..."
  sleep 2
done

A The script terminates immediately without any message.

B The script restarts automatically.

C The script prints 'Terminated' and exits.

D The script ignores SIGTERM and continues running.

💡 Hint

What is the default behavior of SIGTERM if not trapped?

By default, SIGTERM causes the process to terminate immediately without running any custom code.

📝 Syntax

advanced

Identify the syntax error in this trap command

Which option contains the correct syntax to trap SIGUSR1 and run a function named handle_usr1?

Bash Scripting

function handle_usr1() {
  echo "SIGUSR1 received"
}

# trap command here

A trap 'handle_usr1' SIGUSR1

B trap handle_usr1 SIGUSR1

C trap "handle_usr1" SIGUSR1

D trap handle_usr1() SIGUSR1

💡 Hint

trap expects a command string or function name without parentheses.

Option B correctly passes the function name without quotes or parentheses. Options B and C pass a string that calls the function but as a string literal, which works but is less direct. Option B is invalid syntax.

🔧 Debug

advanced

Why does this trap not work as expected?

This script is supposed to print 'Exiting...' when it receives SIGINT, but it doesn't. Why?

Bash Scripting

trap 'echo "Exiting..."' SIGINT

while true; do
  sleep 1
done

A The trap command syntax is wrong; single quotes prevent execution.

B SIGINT cannot be trapped in an infinite loop.

C The trap command is missing a command to exit, so the script continues running after printing.

D The trap command is correct; the script ignores SIGINT because sleep is blocking.

💡 Hint

What happens after the trap command runs?

The trap prints the message but does not exit, so the script continues running. Adding 'exit' after echo fixes this.

🚀 Application

expert

How to safely clean up temporary files on script termination?

You want a bash script to create a temporary file and delete it when the script ends, whether normally or due to signals like SIGINT or SIGTERM. Which trap setup ensures cleanup in all cases?

Bash Scripting

tmpfile=$(mktemp)
echo "Temporary file created: $tmpfile"

# trap commands here

# Simulate work
sleep 30

# End of script

A trap 'rm -f "$tmpfile"; exit' EXIT SIGINT SIGTERM

B trap 'rm -f "$tmpfile"; exit' SIGINT SIGTERM

C trap 'rm -f "$tmpfile"' EXIT SIGINT SIGTERM

D trap 'rm -f "$tmpfile"' EXIT

💡 Hint

EXIT trap runs on script exit regardless of reason.

The EXIT trap runs when the script exits for any reason, including signals that cause termination. Using EXIT alone ensures cleanup. Adding exit in the trap for signals can cause double exit calls or missed cleanup.