(It so happens I’m presenting this at Dallas.rb tonight. Hopefully it can also be useful to those out in internetland too.)

RVM gives you three things:

  • an easy way to use multiple versions of multiple Ruby VMs
  • the ability to manage multiple indpendent sets of gems
  • more sanity

First, let's install RVM:

  • gem install rvm
  • rvm-install
  • follow the directions to integrate with your shell of choice

Now, let's install some Rubies:

  • rvm list known will show us all the released Rubies that we can install (more on list)
  • rvm list rubies will show which Rubies we have locally installed
  • rvm install ree-1.8.7 gives me the latest release of the 1.8.7 branch of Ruby Enterprise Edition
  • rvm install jruby will give me the default release for JRuby
  • rvm use jruby will switch to JRuby
  • rvm use ree will give me Ruby Enterprise Edition
  • rvm use ruby-1.8.6 will give me an old and familiar friend
  • rvm use system will put me back wherever my operating system left me

The other trick that RVM gives us is the ability to switch between different sets of installed gems:

  • Each Ruby VM (JRuby, Ruby 1.9, Ruby 1.8, REE) has its own set of gems. This is a fact of life, due to differing APIs and, you know, underlying languages.
  • rvm use ruby-1.9.1 gives you the default Ruby 1.9 gemset
  • rvm use ruby-1.9.1%acme gives you the gemset for your work with Acme Corp (more on using gemsets)
  • rvm use ruby-1.9.1%wayne gives you the gemset for your work with Wayne Enterprises
  • rvm use ree%awesome gives you the gemset for your awesome app
  • You can export and import gemsets. This can come in handy to bring new people onboard. No longer will they have to sheepishly install gems on their first day as they work through dependencies you long since forgot about.

Some other handy things to peruse:

I also promised you some extra sanity:

  • RVM knows how to compile things, put Rubygems and rake in place, even apply patches and pull from specific tags. You can do more important things, like watch The View or read an eleven part series on pre-draft analysis for the Cowboys.
  • RVM lets you isolate different applications you're working on. Got one app that doesn't play nice with Rails 2.x installed? No problem, create a gem environment for that! Stuck in the spider-web of Merb dependencies? Isolate it in its own environment.
  • RVM makes multi-platform testing and benchmarking easy. You can easily run your test suite or performance gizmo on whatever Rubies you have installed.
  • RVM makes it easy to tinker with esoteric patchlevels and implementations. For instance, feel free to tinker with MagLev or the mput branch of MRI.

A couple other things RVM tastes great with:

  • Using homebrew to manage packages instead of MacPorts
  • Not using sudo to install your gems
  • Managing your dotfiles on GitHub