Don’t do_shortcode

Shortcodes are pretty cool, and the do_shortcode function is pretty neat as it can parse and execute shortcode callbacks from arbitrary strings, but that function invokes a fairly large regex every time it is called.

That regex looks for all registered shortcodes within a string. For each match, it runs a replacement with a callback function, which also take the time to parse the shortcode attributes, before finally calling the actual callback function that’s been registered with add_shortcode.

Regular expressions are pretty fast in PHP, especially for short strings, but do we really have to have WordPress do all that extra work, when all we really intended was to call our shortcode callback function?

echo do_shortcode( '[foo]' ); // Boo
echo foo_shortcode_callback(); // Yey!

I ran a quick search in the plugins directory, using the following regex:


Not the best crafted regex, but it’s supposed to look for calls to do_shortcode followed by a string literal starting with an opening square bracket. Obviously it might get a few false positives for special cases, but it also misses quite a few matches where the shortcode string is put into a variable first.

I found over 600 entries in over 270 plugins, including some of my own. Guilty! So the lesson I learned today is: don’t use do_shortcode when you can use your callback function directly, which is much more efficient.

Native Image Sizing “On the Fly” with WordPress

I tweeted it out not too long ago, and it seems to have gotten people’s attention. So why do WordPress theme developers still use TimThumb? One of the valid reasons seems to be dynamic image sizing. Of course if you’re using TimThumb for post thumbnails in your theme, your life saver is the add_image_size function — you don’t need “dynamic resizing” since all your thumbnails are of equal sizes throughout your theme.

However, the valid reason I seem to have bumped in, is the fact that sometimes you would want to use a specific size for an image, but only once, for one post or page. The add_image_size function here will add a lot of overhead, crunching all the uploaded images into the size you want to use only once. Like a shortcode that can resize and crop an image from your media library to whatever dimensions you tell it to:

[image src="" width="150" height="150"]

Right, a shortcode (argh!) to dynamically resize an image. Fair enough, a lot of premium themes seem to have something similar, but mostly use TimThumb because it’s so simple. However, I’ve created an image shortcode function that resizes and crops images from the media library on the fly using the image_make_intermediate_size function available as early as WordPress 2.5!

It saves the resized image on disk, and returns the absolute URL to that image. Of course you’d want to add things like captions, alt tags and so on, but the basic idea is there. Why is this better than TimThumb?

  • It stores the image files on disk and uses absolute URLs to those images, meaning you won’t have problems hosting your thumbnails on a CDN.
  • It uses functions native to WordPress and works with the WordPress media library, so extra files are deleted when an attachment is deleted — no more junk in your cache/folder.
  • It doesn’t have a zero-day vulnerability :)

There are drawbacks too, like the fact that it’s a shortcode! Although I’m pretty sure we can use the same technique and hook it directly to the content, bypassing the shortcodes madness. Oh, and it doesn’t support remote files too, only the ones in your media library, but that’s a good thing, as we have all figured out by now.

Feel free to fork the Gist on Github and experiment with the code, I’m sure you can think of how to make it better, easier to use and faster. Thoughts and comments welcome, and thank you for stopping by!

Regex Replace in MySQL or lib_mysqludf_preg in Ubuntu Linux

I’ve been working a lot with MySQL lately, especially after the major theme and plugin upgrades on my blog. I was dealing with a bunch of content issues like redundant shortcodes and post meta, URL changes, images directories and more.

One simple solution would be to grab the database dump, perform various search and replace operations and then feed it back in, and my goal was to do that without data loss, without going offline, without sending files back and forth but mainly for learning purposes.

I found a UDF for MySQL called lib_mysqludf_preg and here’s how I got it to run on Ubuntu 11.04, somewhere in a temporary directory:

sudo apt-get install libpcre3-dev libmysqlclient-dev
tar -xf lib_mysqludf_preg-1.0.1.tar.gz
cd lib_mysqludf_preg-1.0.1
sudo ./configure
sudo make install
sudo service mysql restart

So, install some libraries upon which the UDF may depend, download the UDF archive, extract it, browse to what has been extracted, configure, install and restart MySQL (just in case.) If you’re reading this and it’s not 2011, make sure you get the latest version and read the release notes too.

At this point the UDF library is installed but the functions are not available yet, so log in to your MySQL command line, preferably as root and create your new preg_replace function like this:


Voila! And here’s how I removed a shortcode from all posts and pages:

UPDATE wp_posts
  SET post_content = PREG_REPLACE('/[my_shortcode*?.*?]/', '', post_content)
  WHERE post_content LIKE '%[my_shortcode%';

Make sure you backup your database first though before doing any of this. I did! But everything went fine. My next goal is to get the shortcode provided by a syntax highlighting plugin replaced with a <pre> tag. Hopefully I won’t break anything so good luck to me and thank you so much for stopping by!