Run When Done

May 20th, 2014
If you want to run a command when another finishes, the shell can do that for you:
    $ && echo "runs on success"
    $ || echo "runs on failure"
    $ ;  echo "runs either way"
One common thing to do this with is email, so you get a notification:
    $ ; echo done | mail -s done
(This does require your server to be set up for sending mail in a way that won't get rejected, which is actually kind of tricky.)

For years, though, I've gotten annoyed at myself when after a process has been running for a while I wish I had set something else to run after it. Should I kill the process and start it over with &&, or should I let it finish and then run on my own?

It turns out you don't have to choose! Shell job control can do this for you. Just background the first command, and then when you foreground it add the next command:

    $ sleep 10
    [1]+  Stopped                 sleep 10
    $ fg ; echo "finished, exit status is $?"
    sleep 10
(a few seconds of waiting)
    finished, exit status is 0
You can see fg substitutes for the original command, running as long as it would, and passing along the exit status so && and || still work.

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