pipe READ, WRITE;
my $child1 = fork();
unless ($child1) 
  {
    open STDOUT ">&WRITE";
    exec ('cat', $0);
  }

my $child2 = fork ();
unless ($child2) 
  {
    open STDIN "<&READ" or die "Cannot open read filehandle\n";
    exec ('grep', 'grep');
  }

waitpid ($child1, 0);
waitpid ($child2, 0);