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

STDOUT-> autoflush( 1 );
my $external = 'external.pl';

my $sock = IO::Socket::INET-> new(
    LocalHost => '127.0.0.1',
    LocalPort => 5001,
    Proto     => 'tcp',
    Listen    => 5,
    Reuse     => 1
) or die;

for ( my $i = 1;; $i ++ ) {
    print "# $i ";
    system 1, $^X, $external, $i;

    print ' accepting... ';
    my $client = $sock-> accept;

    print 'reading... ', <$client>;

    $sock-> shutdown( 2 );
    $client-> close;
    sleep 1
}


##</code><code>##

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

my $sock = new IO::Socket::INET (
    PeerHost => '127.0.0.1',
    PeerPort => 5001,
    Proto    => 'tcp',
) or die;

print $sock "$ARGV[ 0 ]\n";
$sock-> close;