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Say I want to modify the latter of some concatenated command line options, is it possible without killing the first command?

Specifically I have compile and run scripts executed thusly:

> compile ; run

The compile is in progress (half way through two hour duration), but new information tells me I don't really want the "run" command to run anymore (it launches a lot of background processes I don't want to go clean up).

Is there a way to accomplish this adjustment or should I just be smarter about how I string together commands in the future?

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You should probably be "smarter" and use && instead of ;. – terdon May 2 '13 at 17:03
To clarify, I only know that I want to cancel the run after the compile has been running a while (and I don't want to restart the compile) and I want the run to be cancelled regardless of exit code from the compile. – owenfi May 2 '13 at 17:07
That's the idea, when linked with && the run will not run if the compile is stopped. – terdon May 2 '13 at 17:10
I want the compile to finish for sure, and regardless of compile's exit code I want run not to run. I only came to find this out after an email came in an hour after my command was launched. – owenfi May 2 '13 at 17:15
up vote 3 down vote accepted

Something like

compile && { test -f /path/to/dont_run || run; }

should solve your problem. touch /path/to/dont_run would prevent run from being executed. You can make this more complicated (and more convenient) by e.g. defining a shell function cond_run_cmd which does some check like that, limited to its tty (so that you can have several in parallel) or whatever.

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