#!/usr/bin/perl
use strict;
use warnings;

my $pid = fork;
if ((defined $pid) && ($pid == 0))
{
    exec("sleep 30 >> /dev/null 2>&1 &");
    exit;
}

print "child pid [$pid]\n";

##</code><code>##

$ perl tst.pl
child pid [23367]
$ ps ax | grep sleep
23368 pts/7    S      0:00 sleep 30
23371 pts/7    S+     0:00 grep --colour=auto sleep