From Fedora Project Wiki
This Cookbook will get you started with installing Ruby, and creating simple "Hello, World" projects with some popular frameworks such as Ruby on Rails, Shoes, Sinatra, and others.
This cookbook is based off of a factory-fresh Fedora 18 (Beta) release.
Getting Started
First off, we'll install Ruby. Open a terminal (by going to Applications -> System -> Terminal) and type the following:
sudo yum install ruby