use strict;
use warnings;
use IO::Socket;

my $MAXLEN = 1024;
my $PORTNO = 5151;
my($oldmsg, $newmsg, $hisaddr, $hishost);

my $sock = IO::Socket::INET->new(
                         LocalPort => $PORTNO, 
                         Proto => 'udp')
           or die "socket: $@";

print "Awaiting UDP messages on port $PORTNO\n";
$oldmsg = "This is the starting message.";
while ($sock->recv($newmsg, $MAXLEN)) 
  {
  my($port, $ipaddr) = sockaddr_in($sock->peername);
  $hishost = gethostbyaddr($ipaddr, AF_INET);
  print "Client $hishost said: $newmsg\n";
  $sock->send($oldmsg);
  $oldmsg = "[$hishost] $newmsg";
  }
die "recv: $!";