my $cmd = 'netcat localhost 12345 |';
my $pid = open my $netcat, $cmd
    or die "Couldn't spawn [$cmd]: $!";

for (1..100) {
    my $line = <$netcat>;
    print $line;
};

END {
    # Clean up leftover processes
    kill 9 => $pid
        if $pid;
};