I've started using RVM to manage the multiple installs of Ruby installed on my Mac. However, upon moving to Mountain Lion the default Ruby interpreter has reverted to 1.8.7. So to start with a clean state I nuked my ~/.rvm folder and reinstalled using the instructions at https://rvm.io/rvm/install/
Unfortunately if you've upgraded Xcode to the latest release as well (v4.4) you'll be greeted with this message:
Xcode 4.3+ users
please be warnedonly ruby-1.9.3-p125+ is partially supported--
in case of any compilation issues:
* downgrade to Xcode 4.1* uninstall Xcode and install osx-gcc-installerand reinstall your rubies.
I could probably install Ruby straight from source but I'm assuming I'd run into the same issues RVM did as well, as the problem was at the compilation stage.