I am trying to implement a simple log server in Bash. It should take a file as a parameter and serve it on a port with netcat.
( tail -f $1 & ) | nc -l -p 9977
But the problem is that when the netcat terminates, tail is left behind running. (Clarification: If I don't fork the tail process it will continue to run forever even the netcat terminates.)
If I somehow know the PID of the tail then I could kill it afterwards.
Obviously, using $! will return the PID of netcat.
How can I get the PID of the tail process?
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)
Another option: use a redirect to subshell. This changes the order in which background processes are started, so $! gives PID of the
tail -f $1 > >(nc -l -p 9977) & wait $!