You want to work with Ruby on Mac OS X, but the version already installed on the system is too old for your needs.
It is not a good idea to upgrade the version installed by Apple, as it is there for their own purposes and it’s best to leave it alone. Instead, use rbenv to install sandboxed versions of Ruby in your own home directory.
$ brew update
$ brew install rbenv
$ brew install ruby-build
As instructed by rbenv, also add the following line to your profile (e.g.
if which rbenv > /dev/null; then eval "$(rbenv init -)"; fi
Restart your terminal or
source ~/.bash_profile before continuing.
Figure out the latest stable version of Ruby—at the time of writing it’s
2.0.0-p247—and install that version:
$ rbenv install 2.0.0-p247
$ rbenv rehash
$ rbenv global 2.0.0-p247
And you should be good to go. Remember to run
rbenv rehash after installing any gems that provide commands.