output

PID: 508335 (506711)
Kill: 0
A: 508335 (506711)
B: 508335 (508335)
wait 0: -1
Kill: 1
child exits 508335 (508335)
wait 0: -1
Kill: 1
got sigchild
wait 508335: 0
Kill: 1
wait -1: -1
Kill: 1
wait -1: -1
Kill: 1
Deep child exits 508336 (508335)
wait -1: -1
Kill: 0
wait -1: -1
Kill: 0
wait -1: -1
Kill: 0
wait -1: -1
Kill: 0
wait -1: -1

test.pl

use strict;
use warnings;

use POSIX;

$SIG{CHLD} = sub { print "got sigchild\n"};

my $pid = fork;
if ($pid) {
    print "PID: $pid (" . getpgrp . ")\n";
    for (1 .. 10) {
        my $ok = kill(0, -$pid);
        print "Kill: $ok\n";
        sleep 1;
        my $out = waitpid(-$pid, WNOHANG);
        print "wait $out: $?\n";
    }   

    exit 0;
}

print "A: $$ (" . getpgrp . ")\n";
setpgrp(0, 0); 
print "B: $$ (" . getpgrp . ")\n";

$pid = fork();

if ($pid) {
    sleep 2;
    print "child exits $$ (" . getpgrp . ")\n";
    exit 0;
}

sleep 5;

print "Deep child exits $$ (" . getpgrp . ")\n";

exit 0;