server.pl

use IO::Socket;
use strict;
$| ++;

my $server = new IO::Socket::INET(Timeout => 7200,
                                  Proto => "tcp",
                                  LocalPort => 3000,
                                  Reuse => 1,
                                  Listen => 2);
my $num_of_client = -1;
while (1) {
    my $client;
    do {
        $client = $server->accept;
    } until (defined($client));
    print "new clinet accepted, id = ", ++ $num_of_client, 
		  ", peeraddr = ", inet_ntoa($client->peeraddr()), 
		  ", peerport = ", $client->peerport(), "\n";
    if (!fork) {
        close($server);#this only closes the copy in the child process
        while (1) {
            my $msg;
            $client->recv($msg, 1000);
            if ($msg eq "") {
                die "child $num_of_client is inactive\n"; 
            } else {
                print "rcvd $msg from client ", $num_of_client, "\n";
                sleep(2);
                print $client $msg;
            }
        }
    } else {
        close($client); #this only closes the copy in the parent process, assume the parent no longer need talk to the client
    }
}        

client.pl:
use IO::Socket;
use strict;

my $server = new IO::Socket::INET(Proto => "tcp",
                                  PeerAddr => "localhost",
                                  PeerPort => 3000,
                                  Reuse => 1,
                                  Timeout => 7200)
             || die "failed to connect to server\n";
while (1) {
    print $server "abcd";
    my $msg;
    $server->recv($msg, 1000);
    if ($msg eq "") {
        die "server is not responding";
    } else {
        print "recv'd ", $msg, "\n";
    }
}