Sitemap for main domain and subdomain

<?php
// In .htaccess write string
// RewriteRule ^sitemap\.xml$ /sitemap.php [L]
if (version_compare(phpversion(), '5.3.0', '<')) {
    define("ROOTPATH", dirname(__FILE__));
} else {
    define("ROOTPATH", __DIR__);
}
define("DS", DIRECTORY_SEPARATOR);
header('Content-type: text/xml');
if ($_SERVER['HTTP_HOST'] == 'msk.xxxxx.ru') {
    $controlfile = ROOTPATH . DS . basename('sitemap-msk.xml');
} else {
    $controlfile = ROOTPATH . DS . basename('sitemap-main.xml');
}
echo file_get_contents($controlfile);
?>