Force URLs to lower case in a RewriteRule using PHP. Blogged at http://simonholywell.com/post/2012/11/force-lowercase-urls-rewrite-php.html

.htaccess

RewriteEngine on
RewriteBase /

# force url to lowercase
RewriteCond %{REQUEST_URI} [A-Z]
# ensure it is not a file on the drive first
RewriteCond %{REQUEST_FILENAME} !-s
RewriteRule (.*) rewrite-strtolower.php?rewrite-strtolower-url=$1 [QSA,L]

rewrite-strtolower.php

<?php
if(isset($_GET['rewrite-strtolower-url'])) {
    $url = $_GET['rewrite-strtolower-url'];
    unset($_GET['rewrite-strtolower-url']);
    $params = http_build_query($_GET);
    if(strlen($params)) {
        $params = '?' . $params;
    }
    header('Location: http://' . $_SERVER['HTTP_HOST'] . '/' . strtolower($url) . $params, true, 301);
} else {
    header("HTTP/1.0 404 Not Found");
    die('Unable to convert the URL to lowercase. You must supply a URL to work upon.');
}
exit();