#!/usr/bin/perl

use strict;
use warnings;

my $cmd = qq{nohup ./perl.pl &};

my $pid = fork;  die 'fork failed' unless defined $pid;

if ($pid) {
    print STDERR "parent pid=$$ child pid=$pid\n";
    wait;
    my $sid = getppid;
    system "ps f -s $sid -o pid,ppid,pgrp,sid,cmd";
} else {
    print STDERR "child pid=$$ \$pid=$pid\n";
    setpgrp;
    exec $cmd or die "Bad exec: $!";
}