Here's a server that implements that protocol in its entirety:

#!/usr/bin/perl

# Hello World Server, by Jonadab the Unsightly One A demonstration of
# sockets.  Listens on port 5 for connections made by the hellowc.pl
# client, and answers them with a Hello World response, thus
# demonstrating sockets.  The system running the hellows.pl server
# must have port 5 open.  (Alternately, both the server and client
# could be altered to use another port, but the server must listen on
# the same port the client will connect to.)  To stop the server,
# delete the PID file.  The server will then exit after answering the
# next request.  So, to terminate it immediately, after deleting the
# PID file, run the client one final time to send the last request.
# Be sure to change the $serverhost and $serverlog variables to
# soemthing that makes sense on your system.

$serverhost = 'localhost';
$serverport = 5;
$serverlog = '/var/log/hellows.log';
$pidfile = "hellows.pid";

require 5.002; use sigtrap; use Socket;

use IO::Socket;

open LOG, ">>$serverlog"
  or die "Unable to append to server log $serverlog : $!";

open PID, ">$pidfile" or die "Unable to write to PID file hellows.pid 
+: $!\n"; {
  print PID "$$\n";
  close PID;
}

my $sock = new IO::Socket::INET (
                                 LocalHost => $serverhost,
                                 LocalPort => $serverport,
                                 Proto => 'tcp',
                                 Listen => 1,
                                 Reuse => 5,
                                );

if ($sock) {
  print "Hello World Server is running, waiting for client connections
+...\n";
  while (-e "hellows.pid") {
    my $hellowsock = $sock->accept();
    $_ = <$hellowsock>; {
      if (/[Hh]ello.*[Ww]orld.*[?]/)  {
    print "...";  $canswered++;  if ($canswered % 20 == 0) { print "\n
+"; }
    print LOG localtime(time) . "\tAnswering Hello World request.\n";
    print $hellowsock "Hello, client world!  The server is here!\n";
      }
    }
  }
  close($sock);
}
else {
  print LOG localtime(time) . "\tDIED:  Unable to create socket: $!\n"
+;
  die "Hello World Server unable to create socket: $!\n";
}

print "\nAnswered $canswered requests from Hello World clients this se
+ssion.\n";
[download]

And here is the corresponding client...

#/usr/bin/perl -w
# Hello World Client, by Jonadab the Unsightly One
# Give it an IP address of a machine running the
# hellows.pl server, and it will query that server
# for a Hello World response, demonstrating sockets.
require 5.002; use sigtrap; use Socket;

$serverhost = 'localhost';
$serverport = 5;

use IO::Socket;
my $sock = new IO::Socket::INET (
                                 PeerAddr => $serverhost,
                                 PeerPort => $serverport,
                                 Proto => 'tcp',
                                );
die "Hello World Client unable to create socket: $!\n" unless $sock;
print $sock "Hello, are you there, server world?\n";
print <$sock>;
close($sock);
[download]