Salvare i dati in un file

[trasher666]

$url = 'http://'; 
$url .= $_SERVER['HTTP_HOST']; 
$url .= $_SERVER['SCRIPT_NAME'];

$file = "../config/config.php"; 

if(isset($_POST['submit'])) {

$db_user = $_POST['user']; 
$db_pass = $_POST['pass']; 
$db_name = $_POST['name']; 
$db_host = $_POST['host']; 
$prefix  = $_POST['prefix']; 

$content = " 
\$db_user = '$db_user';\r\n 
\$db_pass = '$db_pass';\r\n 
\$db_name = '$db_name';\r\n 
\$db_host = '$db_host';\r\n 
\$prefix = '$prefix';\r\n";

$fp = fopen($file, "a"); 
fwrite($fp, $content);
fclose($fp); 
header ("location: create_table.php")

} else { 
echo "Errore";
}  
?> 

quindi come applico quello scriptino x l'url allo script?
devo fare

$url = 'http://'; 
$url .= $_SERVER['HTTP_HOST']; 
$url .= $_SERVER['SCRIPT_NAME'];

$file = "$url ./config/config.php"; 

???