#!/usr/bin/perl
$|++;
  use strict;
  use warnings;

  my $pid = fork;

  filter();

  unless($pid == 0) {
      print("$_\n") && sleep 1 for 1..10;
      exit(0);
  }

  sub filter {
      my $pid = open(STDOUT, '|-');
      return if $pid;
      die "Can't fork: $!"
          unless defined $pid;
      while(<STDIN>) {
          print ">> $_";
      }
      exit;
  }