PHP code to obtain website domain name and address_PHP tutorial

function PMA_getenv($var_name) {
if (isset($_SERVER[$var_name])) {
return $_SERVER[$var_name];
} elseif (isset($_ENV[$var_name])) {
return $_ENV[$var_name];
} elseif (getenv($var_name)) {
return getenv($var_name);
} elseif (function_exists('apache_getenv')
&& apache_getenv($var_name, true)) {
return apache_getenv($var_name, true);
}
return '';
}
if (empty($HTTP_HOST)) {
if (PMA_getenv('HTTP_HOST')) {
$HTTP_HOST = PMA_getenv('HTTP_HOST');
} else {
$HTTP_HOST = '';
}
}
echo htmlspecialchars($HTTP_HOST);
?>