Problem:
You are trying to run Ruby on Rails on OS X, and all you ever get is
Rails requires RubyGems >= 0.9.4. Please install RubyGems and try again: http://rubygems.rubyforge.org
When you check gem --version you find that you already have RubyGems 1.1.1, or some other version higher than 0.9.4 that Rails ought to be happy with.
Possible explanation:
At some point you installed MacPorts. MacPorts built and/or installed a redundant version of ruby, even though you didn’t ask it to.
To confirm that this is the problem, type which ruby and see if the answer has /opt in it. If so, yes, MacPorts hosed your Rails/RubyGems. Solution: sudo port uninstall ruby
(I’m pretty confident that MacPorts is at fault here because I installed it for the first time this evening to build bzr, which involves no Ruby, and indeed is from a bunch of Python programmers who would probably sooner drink raw sewage than require Ruby for anything. So thanks, MacPorts.)
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