How to get the PID of a process that is piped to another process in Bash?
Solution 1:
Another option: use a redirect to subshell. This changes the order in which background processes are started, so $! gives PID of the tail process.
tail -f $1 > >(nc -l -p 9977) &
wait $!
Solution 2:
Write tail's PID to file descriptor 3, and then capture it from there.
( tail -f $1 & echo $! >&3 ) 3>pid | nc -l -p 9977
kill $(<pid)