If you want to use Rbenv on OS X you’ll need to install the Xcode command-line tools:

  $ xcode-select --install

Then install Home Brew:

  $ ruby -e "$(curl -fsSL https://raw.github.com/Homebrew/homebrew/go/install)"

Complete Home Brew setup:

  $ brew doctor
  $ brew update

At this point you’ll be able to install rbenv and ruby-build:

  $ brew install rbenv ruby-build

Add the following to your .bash_profile:

  eval "$(rbenv init -)"

Reload your bash profile settings:

  $ source ~/.bash_profile

Then you can install Ruby:

  $ rbenv install 2.1.2

Thanks to John O. at TeamTreeHouse for giving this well written response to this inquiry.

To set as your current version of Ruby run the following command:

  $ rvm use 2.0.0

To make it the default Ruby:

  $ rvm default 2.0.0

or

  $ rvm use 2.0.0 --default