#!/usr/bin/perl

# http://perlmonks.org/?node_id=1192662

use strict;
use warnings;
use IO::Select;

my $childcount = 3;
my $hasterminal = 1;
my %who;
my %pipes;

for my $from (1 .. $childcount)
  {
  for my $to (1 .. $from - 1, $from + 1 .. $childcount)
    {
    pipe( my $readhandle, my $writehandle) or die "$! on pipe";
    $writehandle->autoflush;
    $pipes{$from}{$to}{rh} = $readhandle;
    $pipes{$from}{$to}{wh} = $writehandle;
    }
  }

for my $me (1 .. $childcount)
  {
  if( my $pid = fork ) # parent
    {
    $who{$pid} = $me;
    }
  elsif( defined $pid ) # child
    {
    my $sel = IO::Select->new;
    $me == $hasterminal and $sel->add(*STDIN);
    for my $from (1 .. $me - 1, $me + 1 .. $childcount)
      {
      $sel->add($pipes{$from}{$me}{rh});
      close $pipes{$from}{$me}{wh};
      }
    while(1)
      {
      for my $handle ($sel->can_read)
        {
        defined( my $command = <$handle> ) or exit;
        print "$me got $command";
        $command =~ /^(\d+)\s+(.*\n)/ and $1 != $me and
          print { $pipes{$me}{$1}{wh} } $2;
        }
      }
    }
  else
    {
    die "fork failed with $!";
    }
  }

use Data::Dump 'pp'; pp \%who;
my $pid = wait; # on first exit, kill rest
print "$who{$pid} exited\n";
kill 15, keys %who;
print "$who{$pid} exited\n" while ($pid = wait) > 0;