PHP Grab URL of Current Site, but from a master file hosted on a server

Hey guys basically I have a master file hosted on a server, and what it does is echo a list of links to a bunch of other sites. The set of links it grabs is based on the URL of the current site. The problem I'm having is that using $_SERVER['REQUEST_URI'] on a server produces the url of that server and I want it produce the url of the site 开发者_如何学编程that my master page is loaded in to

<?php
$url = parse_url($_GET['url']); 
$str = $url['host']; 
echo $str; 
if ($str < "g"){ 
    //do stuff 
    echo(" has first character lower than g");
} 
else{ 
     echo(" has not first character lower than g"); 
}

?>

---

You would need to pass the client servers hostname into the $_GET['url'] then look for it in the [query] key outputted by parse_url($_GET['url']);

<?php 
//client side host
file_get_contents('http://server.site.com/masterfile.php?url='.$_SERVER['HTTP_HOST']);
?>

If I understand you correctly. :s