Kill a process and wait for the process to exit

Question

When I start my tcp server from my bash script, I need to kill the previous instance (which may still be listening to the same port) right before the current instance starts listening.

I could use something like pkill <previous_pid>. If I understand it correctly, this just sends SIGTERM to the target pid. When pkill returns, the target process may still be alive. Is there a way to let pkill wait until it exits?

Solution 1

No. What you can do is write a loop with kill -0 $PID. If this call fails ($? -ne 0), the process has terminated:

while kill -0 $PID; do 
    sleep 1
done

(kudos to qbolec for the code)

Related:

• What does `kill -0 $pid` in a shell script do?

Solution 2

Use wait (bash builtin) to wait for the process to finish:

 pkill <previous_pid>
 wait <previous_pid>