Getting Ruby to talk to MySQL was pretty easy in irb:

C:>irb
irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'mysql'
=> true
irb(main):003:0> db = Mysql.connect('localhost', 'root', 'password', 'test')
=> #<Mysql:0x2cc5270>
irb(main):004:0>

But then I tried the very same code from a file:

C:>ruby mysql.rb
./mysql.rb:3: uninitialized constant Mysql (NameError)
        from C:/Ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
        from C:/Ruby/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
        from mysql.rb:2

That require 'mysql' line looks in the current directory first … and I’d used the name mysql.rb for the file I was coding … so my code just included itself, and not the gem I wanted. Doh!