SchmidtHappens

If you've ever had to test an application that you are building with different versions of Ruby or Rails then you know how frustrating it can be. RVM aims to erase that frustration by making it incredibly easy to install multiple versions on the same development machine.

The first thing that you will need to do is install RVM. To do this open a terminal and enter in the following command (please note, you will need to make sure you have git installed):

bash < <(curl -s https://rvm.beginrescueend.com/install/rvm)

Once the install finishes you will be instructed on how you can update your .bash_profile file with a load path to the rvm executable. Once that is done and the file has been saved you can simply type the follwoing into your terminal window to reload your shell (you can also just close and re-open your terminal window):

source .bash_profile

Great, now that we've gotten that out of the way it's super simple to install new Ruby versions. Say you want to install Ruby 1.9.2, all you need to do now is type:

rvm install 1.9.2

To use an installed Ruby use the following (substitute the version you want):

rvm use 1.9.2

Wondering which Ruby versions are available for download?

rvm list known

Want to know which you already have installed?

rvm list

What About Rails?

Now that you know how to install different Ruby versions we can talk about how you can have different Rails environments. Let's say we have installed Ruby 1.9.2 and we are currently using that version and we want to try out Rails 3.1 without messing with any of our Rails 2.x applications. To do this we need to create what RVM calls a gemset. This will create a separate container where we install gems for a particular purpose.

rvm gemset create rails31

This will create a new gemset called "rails31". Now all we need to do is switch into that gemset:

rvm gemset use rails31

This will place us into the rails31 gemset. You can see this by running gem list which will return a very short list of gems. Now we can install Rails 3.1. WARNING!!! When you install gems with RVM you will never want to use `sudo' when calling `gem install' while using one of the RVM installed rubies. If you do bad things will happen and kittens will die. The following command assumes that the Rails team hasn't released another version of Rails since 3.1.

gem install rails

Now we have Rails 3.1 installed in it's own contained gemset. We can now play around with it and not worry how installing this will effect our other applications running older Rails version. To get back out of this gemset simply call (assuming we still want to use the 1.9.2 Ruby version):

rvm 1.9.2

There is a lot more information on RVM and how to use it including some pretty cool (and useful) advanced features. I highly recommend you look over the documentation on RVMs website.

Something missing? Need more explanation? Let me know in the c-c-c-comments!