Install older ruby with modern command line tools on OS X Lion/Mountain Lion

install.sh

# Sources:
# http://robots.thoughtbot.com/post/27985816073/the-hitchhikers-guide-to-riding-a-mountain-lion
# https://github.com/sstephenson/ruby-build#special-environment-variables

# Install command line tools from https://developer.apple.com/downloads/index.action. Then:

sudo chown -R `whoami` /usr/local

brew update
brew upgrade rbenv
brew upgrade ruby-build

brew tap homebrew/dupes
brew install apple-gcc42

# Now you are ready to install older versions of ruby. If ruby-build doesn't detect your apple-gcc42 binary,
# use the command below

CC=/usr/local/Cellar/apple-gcc42/4.2.1-5666.3/bin/gcc-4.2 rbenv install 1.8.7-p371