Introduire une variable dans un lien

$ip = $_POST['ip'];
$port = $_POST['port'];
$url=('http://monsite.com/playeronline.php?ip='.$ip.'&port='.$port.''
echo $url;
$playeronline = file_get_contents($url); 
echo $playeronline;

<?php
session_start();
$ip = $_POST['ip'];
$port = $_POST['port'];
$url='http://monsite.com/playeronline.php?ip='.$ip.'&port='.$port.'';
echo $url."<br>";
$playeronline = file_get_contents($url); 
echo $playeronline;
?>

Many sites, not only parked domains use some mechanism to block basic requests without valid browser headers.

Try to use stream context that send that required headers like a browser like this

$url = "http://buythisdomain.com/"
$context = stream_context_create(array(
    'http' => array(
        'method' => "GET",
        'header' =>
            "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n" .
            "Accept-Language: en-US,en;q=0.8\r\n".
            "Keep-Alive: timeout=3, max=10\r\n",
            "Connection: keep-alive",
        'user_agent' => "User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.66 Safari/535.11",
        "ignore_errors" => true,
        "timeout" => 3
    )
));
file_get_contents($url, false, $context);