A function to redirect uppercase URLs to lowercase.

force-lowercase-urls.php

/**
 * Changes the requested URL to lowercase.
 *
 * Only if URL does not include a filename or query variable.
 */
function force_lowercase_urls() {
  // Grab requested URL
  $url = $_SERVER['REQUEST_URI'];
  // If URL contains a period, halt (likely contains a filename and filenames are case specific)
  if ( preg_match('/[\.]/', $url) ) {
    return;
  }
  // If URL contains a question mark, halt (likely contains a query variable)
  if ( preg_match('/[\?]/', $url) ) {
    return;
  }
  if ( preg_match('/[A-Z]/', $url) ) {
    // Convert URL to lowercase
    $lc_url = strtolower($url);
    // 301 redirect to new lowercase URL
    header('Location: ' . $lc_url, TRUE, 301);
    exit();
  }
}

This is an excellent solution. ;)

I've tried your solution, and in general it works fine. Only reason why I don't use it is that if the URL has a query string the base URL without the query string is not set to lowercase. In this form it's pitily not suitable for my demands.
Is there a reason you're not using SCRIPT_URI and QUERY_STRING from $_SERVER?
I now set up a short script on my own to fit my needs, so far it works fine for me:

if( !empty($_SERVER['SCRIPT_URI']) && $_SERVER['SCRIPT_URI'] !== strtolower($_SERVER['SCRIPT_URI']) ) { $redirect = strtolower($_SERVER['SCRIPT_URI']); if(!empty($_SERVER['QUERY_STRING'])) { $redirect.= "?".$_SERVER['QUERY_STRING']; } header('Location: ' . $redirect, TRUE, 301); exit(); }

@SinnlosS no good reason, this is just an old gist I created 5 years ago and probably didn't spend much time slapping together 😄

I have a free plugin in the WP marketplace with this same functionality and I may have resolved the issue there but I can't recall:

• https://wordpress.org/plugins/wp-force-lowercase-urls/
• https://github.com/joshbuchea/wp-force-lowercase-urls/blob/master/wp-force-lowercase-urls.php