use IO::Socket::INET;

for my $port ( 1..1024 ) {
    $sock = IO::Socket::INET->new(PeerAddr => '127.0.0.1',
                                 PeerPort => $port,
                                 Proto    => 'tcp',
                                 Timeout  => 2);
    print "Port $port ", $sock ? "OPEN\n" : "CLOSED\n";
    $sock->close if $sock;
}