■

Perl 
#!/usr/bin/perl

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

my $udpa = IO::Socket::INET->new(
	Proto => 'tcp', 
	PeerAddr => 'localhost',
	PeerPort => 5000,
);
unless ($udpa) {
	die "$!";
}
$udpa->print("aaaaaaaaaaaaaaaaaaa\n");
print $udpa->getline;
$udpa->close;

## http://x68000.q-e-d.net/~68user/net/module-3.html を少し改造
use IO::Socket;
    use IO::Select;
     
     $port = shift || 5000;
     
    $listening_socket = IO::Socket::INET->new(LocalPort => $port,
                                              Listen    => SOMAXCONN,
                                              Proto     => 'tcp',
                                              Reuse     => 1,
                                             );
    
    if ( ! $listening_socket ){
        die "listen err$!\n";
    }
    
    $selecter = IO::Select->new;
    $selecter->add($listening_socket);
    
    while (1){
        ($active_socks) = IO::Select->select($selecter,undef,undef,undef);
        
      foreach $sock (@{$active_socks}){
            if ( $sock == $listening_socket ){
                print "NEW CLIENT\n";
                $new_sock = $listening_socket->accept;
                $selecter->add($new_sock);
            } else {
                $buf = <$sock>;
                if ( $buf ){
                    chomp $buf;
                    print "NEW MESSSAGE\n";
                    print $buf . "\n";
                    print $sock $buf . "\n";
                    $sock->flush();
                } else {
                    $selecter->remove($sock);
                    $sock->close();
                }
            }
        }
    }