MacOS – What version of Ruby ships with OS X 10.8 (Mountain Lion)

This worked for me.

Update ~/Library/Application\ Support/Sublime\ Text\ 2/Packages/Ruby/Ruby.sublime-build

{
  "env":{
      "PATH":"${HOME}/.rvm/bin:${PATH}"
  },
  "cmd": ["rvm-auto-ruby", "$file"],
  "file_regex": "^(...*?):([0-9]*):?([0-9]*)",
  "selector": "source.ruby"
}

The env part will add rvm-auto-ruby into the $PATH and the cmd will execute rvm-auto-ruby yourfile.rb when you press Cmd-B. You and add options in between rvm-auto-ruby if you want, like this `”cmd”: [“rvm-auto-ruby”, “-S”, “$file”].

From here:
http://rubenlaguna.com/wp/2012/12/07/sublime-text-2-rvm-rspec-take-2/

No don't update the Apple supplied ruby as that could affect existing ruby scripts and will get overridden in a System Upgrade.

To install ruby see the Download Ruby page from the ruby language website (the main page of which you should have bookmarked)

The two ways that you should consider are

1. Download the RVM. Then edit your .bash_profile to put the bin path of the install at the front of your PATH.

2. Use a package manager (e.g. Macports, Fink, Homebrew) and put their path at the front of your PATH ( I would use this only if you have C libraries that you need as well)