[php] Get current domain

I know this might not be entirely on the subject, but in my experience, I find storing WWW-ness of current URL in a variable useful.

Edit: In addition, please see my comment below, to see what this is getting at.

This is important when determining whether to dispatch Ajax calls with "www", or without:

$.ajax("url" : "www.site.com/script.php", ...

$.ajax("url" : "site.com/script.php", ...

When dispatching an Ajax call the domain name must match that of in the browser's address bar, otherwise you will have Uncaught SecurityError in console.

So I came up with this solution to address the issue:

<?php
    substr($_SERVER['SERVER_NAME'], 0, 3) == "www" ? $WWW = true : $WWW = false;

    if ($WWW) {
        /* We have www.example.com */
    } else {
        /* We have example.com */
    }
?>

Then, based on whether $WWW is true, or false run the proper Ajax call.

I know this might sound trivial, but this is such a common problem that is easy to trip over.