Capture command output for n seconds, then detach it (run in the background) 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?

(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)