Monitoring external process: Exit when STDOUT matches pattern

Question

I'm running a system command and waiting for output matching a specific pattern, e.g:

open(my $fh, '-|', 'echo line 1; sleep 20; echo line 2');
while (<$fh>) {
    print && last if /1/;
}
close $fh;

This will print line 1 and leave the loop but won't exit until the external command has completed.

How can I allow the script to exit immediately after matching the required output?

Answer 1

You can send TERM signal to the PID and then close file handle without waiting,

my $pid = open(my $fh, '-|', 'echo line 1;sleep 5; echo line 2') or die $!;
while (<$fh>) {
    print && last if /1/;
}
kill TERM => $pid;
close $fh;