When I got the Macbook Pro in March, I immediately installed Ruby, Rails, Subversion, etc, using this tutorial from Hivelogic. http://hivelogic.com/narrative/articles/ruby-rails-mongrel-mysql-osx
They’ve done a good job of keeping it up to date, but one problem I noticed is that the MySQL gem instructions don’t work anymore. When the article was first written, it contained steps to remedy a minor installation problem. However, enough users reported that the problem no longer existed so it was removed.

Today, I encountered that problem again, and thought I’d share the solution. If you’re getting an error when you do

  asudo gem install mysql -- --with-mysql-dir=/usr/local/mysql

You’ll need to do the following to fix it.

First, look at where the gem says it’s left its files.

  Gem files will remain installed in /usr/local/lib/ruby/gems/1.8/gems/mysql-2.7 for inspection.

So in my case, I’ll do

  cd /usr/local/lib/ruby/gems/1.8/gems/mysql-2.7

Then I’ll edit the file ‘mysql.c’ in that folder and add one line at the top of the file:

  #define ulong unsigned long

Then, I just run

  sudo make
  sudo make install

The original fix for this comes from
http://jlaine.net/2006/10/3/installing-ruby-mysql-driver-on-os-x but the instructions there are a little backwards. I hope this solution will help others having a similar problem.