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Say I have a server writing stdout to a consumer

my server |  upon 'some pattern' --exit=0

so basically when the consumer reads stdout, and sees a certain pattern it will exit. my question is - when it exits, how I clean up the pipeline and potentially make the server a background process?

Maybe this is just a better way to do it:

( my server &> $file ) &

while true; do
  cat $file | upon 'some pattern' --exit=0
done

basically instead of sleep 5 seconds or what not, I am hoping to use a more evented approach, that guarantees the server is ready.

  • What do you mean by "clean up the pipe"? If you want to redirect the output of `server` to `/dev/null` when a pattern is seen by the right hand of the pipeline, I don't think that's possible, in a clean way. You can start the server in background and have the right hand transform itself in a lightweight `cat` upon seeing the pattern. Eg: `{ server & } | { sed /pattern/q; cat >/dev/null & }`. And there are hacks like [this](https://unix.stackexchange.com/a/501974/308316) to force redirect file descriptors from a running process. –  May 18 '19 at 17:37
  • well I'd rather avoid using the temp file and the while loop...i assume exit breaks out of the loop but doesnt stop the outer script –  May 18 '19 at 19:07
  • your temp file / poll (actually busy loop poll) approach is worse IMHO than the extra cat solution from my comment. –  May 18 '19 at 19:10
  • another approach is `server > tmpfile & tail -f tmpfile | grep -m1 pattern` but then the server will keep writing to `tmpfile` and filling up your disk. –  May 18 '19 at 19:16

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