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I need to run a certain command (ngrok in this case) for a few seconds, capture all the output, filter out some variables and then detach the process, making it run invisibly in the background. How can I do that?

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  • capture the output where? In a file, shell variable? Jul 29, 2017 at 17:34
  • file, variable, doesn't matter Jul 29, 2017 at 17:35

1 Answer 1

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(cmd &) | (timeout --foreground 2 cat; cat > /dev/null &)

Would show you the output of cmd for 2 seconds and then return, with cmd running in background with its output going to /dev/null.

You can redirect that to a file or store in a variable with:

var=$(that command)
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  • ngrok output can't unfortunately get captured like this, because it's sort of like apt output line updating, which doesn't get captured in a file. So this solution doesn't output anything. Thanks anyway! Jul 29, 2017 at 18:09
  • I was able to make it work using this solution when I disabled the buffering via the expect's unbuffer. Thanks! Jul 29, 2017 at 18:15
  • @freemanovec, you may try to use stdbuf -o0 before unbuffer if available as unbuffer has a few issues. Jul 29, 2017 at 18:36

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