use warnings;
use strict;
$|=1;

my $cmd = q{
  perl -e 'print "child: id after exec: $$\n";
  print "child: sees processes...\n " ,
     grep { m/perl/ }
     `ps ax` , "\n";
  '
};

print "parent: pre-fork id $$\n";

if ( my $pid = fork ) {
  # this is parent code
  print "parent: post-fork id $$\n";
  print "parent: return from fork is: $pid\n";
  sleep 3;
  print "parent: still here, with id $$\n";
  print "parent: sees processes...\n " ,
     grep { m/perl/ }
     `ps ax` , "\n";
} else {
  # this is child code
  die "cannot fork: $!" unless defined $pid;
  print "child believes it is: $$\n";
  exec( $cmd ) # replaces child with a new perl: pid shouldn't change, right?
}

##</code><code>##

   parent: pre-fork id 27516
   child believes it is: 27517
   child: id after exec: 27518
   parent: post-fork id 27516
   parent: return from fork is: 27517
   child: sees processes...
   27516 pts/1    S+     0:00 /usr/bin/perl /home/doom/bin/testes-forkitude
   27517 pts/1    S+     0:00 sh -c perl -e 'print "child: id after exec: $$\n";?  print "child: se
   27518 pts/1    R+     0:00 perl -e print "child: id after exec: $$\n";?  print "child: sees proc
   parent: still here, with id 27516
   parent: sees processes...
   27516 pts/1    R+     0:00 /usr/bin/perl /home/doom/bin/testes-forkitude

##</code><code>##

   parent: pre-fork id 7253
   child believes it is: 7254
   parent: post-fork id 7253
   parent: return from fork is: 7254
   child: id after exec: 7254
   child: sees processes...
   7253 pts/3    S+     0:00 /usr/bin/perl /home/doom/bin/testes-forkitude
   7254 pts/3    R+     0:00 perl -e print "child: id after exec: $$\n";?  print "
   parent: still here, with id 7253
   parent: sees processes...
   7253 pts/3    S+     0:00 /usr/bin/perl /home/doom/bin/testes-forkitude
   7254 pts/3    Z+     0:00 [perl] <defunct>