How to send signal to a bash script from another shell

Question

I start the following script which I run in a bash shell(let's say shell1) in foreground and from another shell(shell2) I send the kill -SIGUSR1 pidof(scriptA). Nothing happens. What am I doing wrong ? I tried other signals(SIGQUIT etc) but the result is same.

test_trap.sh

function iAmDone { echo "Trapped Signal"; exit 0 } 
trap iAmDone SIGUSR1 
echo "Running... " 
tail -f /dev/null # Do nothing

In shell1

./test_trap.sh

In shell2

kill -SIGUSR1 ps aux | grep [t]est_trap | awk '{print $2}'

Bionics

Attention : @dennis-williamson – Bionics

Answer 1

The trap is not executed until tail finishes. But tail never finishes. Try:

tail -f /dev/null &
wait

The trap will execute without waiting for tail to complete, but if you exit the tail will be left running. So you'll probably want a kill $! in the trap.

Rocambole

Thanks! That solves the problem but I don't understand "The trap is not executed until tail finishes" part. – Bionics

That's how the shell works. When a signal arrives, any traps that are set for that signal do not execute until the process that is running returns. If you want the trap to execute immediately, the shell should be sitting in wait. – Rocambole