Question

I run a script like:

sleep 20 &
PID=$!
kill -9 $PID >/dev/null 2>&1

I dont want the script show the output like:

line 51: 22943 Killed  sleep

I have no idea why this happen, I have redirect the output to /dev/null

Answer 1

The message isn’t coming from either kill or the background command, it’s coming from bash when it discovers that one of its background jobs has been killed. To avoid the message, use disown to remove it from bash’s job control:

sleep 20 &
PID=$!
disown $PID
kill -9 $PID