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

my $PORT = 53123;
my $num  = 0;

my $sock = new IO::Socket::INET(
    LocalHost => '127.0.0.1',
    LocalPort => $PORT,
    Proto     => 'tcp',
    Listen    => 5,
    Reuse     => 1,
) or die;
binmode $sock;

while ( my $client = $sock-> accept ) {
    my $str = do { local $/; <$client> };
    die "$num\n" unless $str eq '123';
    print "$num\n" unless $num ++ % 1000;
}

##</code><code>##

use strict;
use warnings;
use autodie;
use IO::Socket::INET;

my $PORT = 53123;

while () {
    my $sock = new IO::Socket::INET(
        PeerHost => '127.0.0.1',
        PeerPort => $PORT,
        Proto    => 'tcp',
    ) or die;
    binmode $sock;
    print $sock '123';
    $sock-> close;
    select( undef, undef, undef, 0.01 )
}