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) {
    $file = str_replace('http://', '', $file);
    $file = str_replace('https://', '', $file);
    $file = str_replace($_SERVER['SERVER_NAME'], '', $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;
}