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Run When Done

May 20th, 2014
tech

If you want to run a command when another finishes, the shell can do that for you:

    $ long_running_process.sh && echo "runs on success"
    $ long_running_process.sh || echo "runs on failure"
    $ long_running_process.sh ;  echo "runs either way"
One common thing to do this with is email, so you get a notification:
    $ long_running_process.sh ; echo done | mail -s done jeff@jefftk.com
(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 && something_else.sh, or should I let it finish and then run something_else.sh 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
    ^Z
    [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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