How to get the PID of a process that is piped to another process in Bash?

how about this:

jobs -x echo %1

%1 is for first job in chain, %2 for second, etc. jobs -x replaces job specifier with PID.

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 process.

tail -f $1 > >(nc -l -p 9977) &
wait $!