Question

In my web development workflow, I have two processes:

1. watching my folder for changes
2. previewing my site in the browser

I want to be able to run them and then later stop them both at the same time. I’ve seen everyone suggesting using the ampersand operator:

process_1 & process_2

But pressing Ctrl + C only stops the second one. I have to kill the first one manually. What am I missing in this approach?

Answer 1

You can have the foreground script explicitly kill the subprocesses in response to SIGINT:

#!/bin/sh
trap 'kill $pid1 $pid2' 2
cmd1 &
pid1=$!
cmd2 &
pid2=$!
wait

There is a race condition in this example: if you send SIGINT to the parent before pid1 is assigned, kill will emit a warning message and neither child will be terminated. If you send SIGINT before pid2 is assigned, only the process running cmd1 will be sent the signal. In either case, the parent will continue running and a second SIGINT can be sent. Some versions of kill allow you to avoid this race condition by sending a signal to the process group using kill -$$, but not all versions of kill support that usage. (Note that if either child process does not terminate in response to the signal, the parent will not exit but continue waiting.)