Why I use chruby instead of RVM or rbenv

Thursday the 1st of March, 2018

When you’re working with multiple Ruby projects, you often end up needing to run different versions of Ruby. Version managers help make this easier, and there are three well-known choices for Ruby: RVM, rbenv, and chruby.

Here’s why I use chruby.

chruby is simpler and easier to understand

chruby is essentially a very small shell script that sets a few environment variables (mostly $PATH) to point at a given install of Ruby. It also has a separate, optional, script to auto-switch ruby versions when changing directories. Both of the scripts are short enough and clear enough that I can read and follow what they’re doing. It doesn’t do anything more than that, itself; you use ruby-install (a completely separate tool) to install versions of Ruby. Or install them by hand. Or whatever.

RVM and rbenv, on the other hand, do things like overriding cd so that it can switch rubies “magically”. They also install shims of commands like gem, ruby, and others that dynamically look up the available Rubies. These sometimes have bugs, or aren’t entirely transparent. RVM does a bunch of this to enable features like Gemsets, but most of that functionality has been surpassed by Bundler. rbenv is a bit better, but the shims still require “rehashing” (updating) whenever you install a new gem that offers executables.

In short: I’ve had weird issues in the past that ended up being down to RVM or rbenv components misbehaving. With chruby, there’s nothing actually there other than a script that tweaks environment variables, so issues are pretty much nonexistent.

What you need to do to use chruby

Getting started with chruby is pretty easy and, because it’s designed to be self-contained and loosely coupled, it’s easy to back out if change your mind. Here’s how to install it and set it up with your first Ruby version:

  1. Install chruby and ruby-install. This doesn’t install a version of Ruby, just chruby itself and ruby-install. I do this with a Homebrew Brewfile.
  2. Use ruby-install to install a version of Ruby, then install Bundler for that version of Ruby: 
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    ruby-install ruby-2.5.0
~/.rubies/ruby-2.5.0/bin/gem install bundler
  3. Enable chruby in your shell (like this). This means you can run chruby ruby-2.5.0 or chruby system (for example) to switch to that version of Ruby, wherever you are. Just running chruby will list the available versions (not including “system”).
  4. Set your default Ruby by calling chruby ruby-2.5.0 in your ~/.bash_profile. Without this, you’ll need to manually call chruby every time you want to use something other than the system Ruby.
  5. You can also optionally set up chruby to auto-switch Ruby versions based on the presence of .ruby-version files in folders you cd to by adding it to your ~/.bash_profile, too (like this). With this enabled, you can also set your default Ruby with a ~/.ruby-version instead of running chruby in your shell.

You can see 3 and 5 in my bash profile. I haven’t done step 4 because I have a .ruby-version in my home directory.

chruby is a simple tool that does one thing well

Like all good Unix tools, chruby does one thing well and works with other programs to achieve its goal. It doesn’t try to take over, or insert itself between its user and Ruby, it just helps switch between versions of the language.

I hope this helps you get started with chruby. If you want to know more, chruby’s documentation is pretty clear and easy to follow.