Recommended startup tutorial
I’ve gotten several requests for OS X setup help by Ruby Newbies. One of the better setup tutorials is Daniel Kehoe’s Install Ruby on Rails for OS X Mavericks. I’m sure he’ll have a tutorial out for Yosemite shortly after release, but the fundamentals are the same.
First, everyone needs a package manager, and the one I like is Homebrew. The name is whimsical, but it works quite well, and there are lots of packages to choose from. Homebrew is nice and will install programs in the /usr/local/bin directory–make sure your $PATH has /usr/local/bin early in the list.
You’ll need Xcode, which is Apple’s development environment, and you’ll need it for the command line tools which include the compilers and other programs used by Homebrew to compile and install downloaded programs.
The distributed source code control program Git is highly recommended. Install it with Homebrew.
You’ll need a Ruby Version Manager to handle upgrading OS X’s ancient version of Ruby. I highly recommend that you leave OS X system compilers, interpreters, and gems alone. Don’t install any of these using sudo (with the exception of Xcode, and you really want to install Xcode from the App Store if you are a newbie). The main choices are RVM, rbenv, and chruby. I’d go with RVM at first. Although it is a Ruby version manager, it also installs new rubies, and it provides gemsets. Gemsets are not really needed anymore, as Bundler can work with all your gems in one place, but conceptually it is easy to see how things work with gemsets. Later, if you want, you can migrate to rbenv (which I use) and decide how you want to handle gems for multiple projects (I am a fan of the Vendor Everything Philosophy).
After you have a Ruby Version Manager, install the rubies of your choice. I’d go with a Ruby version at or above 1.9.3 as a minimum. Earlier version of Ruby have slightly different behaviors, and you want to learn with the current behavior (the versions above 2.0 are slightly slightly different, but the main changes are in 1.9.3).
And that should get you up and running!