Just bind to the port. Trying to connect to the socket is slower and less reliable.

use strict;
use warnings;

use Errno  qw( EADDRINUSE );
use Socket qw( PF_INET SOCK_STREAM INADDR_ANY sockaddr_in );

sub port_available {
    my $family = PF_INET;
    my $type   = SOCK_STREAM;
    my $proto  = getprotobyname('tcp')  or die "getprotobyname: $!";
    my $host   = INADDR_ANY;  # Use inet_aton for a specific interface
    my $port   = '8888';

    socket(my $sock, $family, $type, $proto) or die "socket: $!";
    my $name = sockaddr_in($port, $host)     or die "sockaddr_in: $!";

    bind($sock, $name) and return 1;
    $! == EADDRINUSE   and return 0;
    die "bind: $!";
}

print port_available() ? "available\n" : "in use\n";
[download]

Tested on linux and Windows.

I would still like to know how this is useful to you.