How to know if a background job is finished?

Question

I invoke a script (do_something) in background via another script (do_manythings) as below.

nohup do_something &

How would I know in the parent script (do_manythings) that the job invoked (do_something) has been done?

Answer 1

If you want to fire off a background job, do some other stuff, then stop and wait for the background job to finish, you can do

nohup do_something &
pid=$!
...more stuff...
wait $pid

Alternatively, you can test for the job having exited like this:

nohup do_something &
pid=$!
...more stuff...
ps -p $pid > /dev/null
[ $? == 1 ] && echo "it's gone, buddy!"

Answer 2

You can also look for start-stop-daemon (examples in /etc/init.d/) if you want to use do_something as a daemon.