The other day I decided to dust off this Octopress blog that I had started back in the Spring of this year to find that my rake tasks weren’t running properly. After a brief search of the web it seemed that outdated versions of Ruby were to blame. However, I still needed to maintain these older versions of Ruby for other projects I’m working on. With that in mind, I set about learning how to manage multiple versions of Ruby on my Mac and stumbled across rbenv.

First I’ll go over why I chose to use rbenv over similar tools like RVM and then get into how to install and use rbenv. The main reasons I choose to go with rbenv are:

• it’s light compared to RVM
• I can set application-specific Ruby versions
• no configuration file!
• easier to get set up and back to work

What rbenv does is essentially create a sandboxed Ruby environment for our project in which we get to control which version of Ruby is run, separately from the version that may be the default for our system. To start using rbenv we will want to have Homebrew installed and up to date. After making sure that Homebrew is up to date we are ready to install rbenv! You can see that rbenv also installs ruby-build, a plugin that allows us to install multiple versions of Ruby and enables rbenv to specify which version to use for the current project.

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$ brew update
$ brew install rbenv ruby-build

When the above completes, we’re ready to install our desired version(s) of Ruby by running:

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$ rbenv install 2.4.2

We’ll also need to run the following command to install the shims required for all the Ruby executables that rbenv is aware of. We will want to run the rehash command each time we install a new version of Ruby or a gem that provides commands.

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$ rbenv rehash

After restarting our terminal we should be able to specify which version of Ruby we’d like to run in our project by cd-ing into the root folder of the project and running the following command:

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$ rbenv local 2.4.2

We can verify the current active Ruby version by running:

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$ rbenv version

And that’s it! We’re now able to install and manage multiple versions of Ruby on a per-project basis with minimal fuss.