PHP CSS&JS auto-versioning function.

.htaccess

# CSS/JS auto-versioning
RewriteEngine On
RewriteRule ^(.*)\.[\d]{10}\.(css|js)$ $1.$2 [L]

auto_version.php

<?php
/**
 *  Given a file, i.e. /css/base.css, replaces it with a string containing the
 *  file's mtime, i.e. /css/base.1221534296.css.
 *
 * @param  string $file The file to be loaded. Must be an absolute path (i.e.
 *                      starts with slash).
 * @return string
 */
function auto_version($file) {
	$fileorig = $file;
	$file = str_replace('http://', '', $file);
	$file = str_replace('https://', '', $file);
	$file = str_replace($_SERVER['SERVER_NAME'], '', $file);
	if ((strpos($file, '/') !== 0) && ($fileorig == $file))
		$file = '/' . $file;
	$full_file = $_SERVER['DOCUMENT_ROOT'] . $file;

	if (strpos($file, '/') !== 0 || !file_exists($full_file)) {
		$full_file = substr($_SERVER['SCRIPT_FILENAME'], 0, -strlen($_SERVER['SCRIPT_NAME']));
		$full_file .= $file;

		if (!file_exists($full_file)) {
			return $file;
		}
	 }

	 $mtime = filemtime($full_file);
	 $new_file = preg_replace('{\\.([^./]+)$}', ".$mtime.\$1", $file);
	 return $new_file;
}