Update: I have now written a WordPress plugin that does all of this for you. Please use this plugin instead.
I’ve just changed my permalink structure for my blog to something a bit prettier. In the process, I realised that some previously-working permalinks weren’t operating any more, despite having a plugin set up to maintain old permalinks.
WordPress is fairly good at figuring out what viewers are requesting when a post can’t be found immediately – for example, if you’re using a permalink structure with an ID number in it, and the requested ID is incorrect, WordPress seems to be able to redirect to the correct address.
However, it’s not 100%, as I recently realised.
Consequently, a few pages were heading to the 404 page, which isn’t ideal. I changed my template’s 404 page to do a search for what the viewer was really after, and redirect them there. If it can’t find an exact match, it’ll perform a search with keywords extracted from the URL. If it finds a single result, it’ll redirect, otherwise it’ll put up a few results as suggestions on the 404 page.
It also works as a nice search shortcut. Try it: http://atastypixel.com/wordpress 404 redirect
It’s all done in the 404 handler in the WordPress theme (wp-content/themes/themename/404.php). It should probably be a plugin, and maybe I’ll make it one some time. For now, put this code above the get_header() in your 404.php:
<?php
global $wp_the_query;
// Construct search term
$search = preg_replace(array(“@[_-]@”, “@.html$@”),
array(” “, “”),
urldecode(basename($_SERVER[“REQUEST_URI”])));
// Search for posts with exact name, redirect if one found
$posts = $wp_the_query->query(array(“name” => $search));
if ( count($posts) == 1 ) {
wp_redirect(get_permalink($posts[0]->ID), 301);
exit();
}
// Do a general search, redirect if exactly one result
$posts = $wp_the_query->query(array(“s” => $search));
if ( count($posts) == 1 ) {
wp_redirect(get_permalink($posts[0]->ID), 301);
exit();
}
?>
And then if you want to list some suggestions as well, use this code to do so, somewhere after the above code:
<?php if (count($posts) > 0) : ?>
Or, try one of these links:
<p>
<?php foreach ( $posts as $post ) : ?>
<a href=“<?php echo get_permalink($post->ID); ?>”><?php echo $post->post_title; ?></a><br/>
<?php endforeach; ?>
</p>
<?php endif; ?>