Getting Started With Ruby

Getting Started With Ruby

  • 09 December 2018 | 

  • ruby.

I love Ruby, it’s very satisfying and developer-friendly to use. Ironically, despite its focus on developer friendliness, it can be a real pain to set up properly, which leaves a sour taste in the mouth for new users. In this post, we’ll walk through setting up Ruby on your Mac (Linux guide coming soon!).

First Things First

One of the reasons that setting up Ruby can be annoying is that there are so many different versions of Ruby. Which do you choose? What if you picked the wrong one? What if you want to run software that was written in a different version to the one you have? Before we answer these questions, let’s look at why there are so many different versions of Ruby.

Ruby, like everything, is imperfect. The language has evolved over the last twenty-something years into what it is today. As bug-fixes, improvements and features have been added to the language, they have been released into the wild in new Ruby versions. This keeps a sane, chronological order in place and allows software that was written in older versions to keep working becuase those versions haven’t changed, they’ve just been superseded.

Okay, so how do you deal with this mess? The short answer is you don’t. You use a Ruby version manager to deal with it for you. There are several popular version managers to choose from: rvm, rbenv and chruby (I’m sure there are several others I’m unaware of as well).

I’ve used all of them, but I prefer rbenv, so that’s what we’ll use here. (As a quick aside, if you’ve installed any other Ruby version manager previously but you want to follow along now, you should make sure to uninstall it completely from your system before you continue. Rbenv is likely to be incompatible with it and you may get unexpected behaviour.)

Installing Rbenv

On macOS it’s a doddle, you can do it via homebrew.

$ brew install rbenv

Once rbenv has been installed, you then set it up like so:

$ rbenv init

This makes sure rbenv is set up and running in your terminal environment. Now you’re ready to install Ruby!

Installing Ruby

You can install as many versions of Ruby you like now using the rbenv install command.

To see a list of Ruby versions available for installation, run rbenv install -l. The list this prints out is quite long and comprehensive. For our purposes, we’re really only interested in the plain Rubies up the top (the ones that only have numbers in their version names). The others (like JRuby, etc) are different implementations of Ruby written by the wider Ruby community.

Let’s install Ruby 2.5.1

$ rbenv install 2.5.1

Selecting a Ruby Version

It’s all well and good to have multiple Ruby versions installed, but how do you switch between them, and how does rbenv know when to use the right one for your project?

Rbenv acheives this through the use of three variables: rbenv global, rbenv local and rbenv shell.

Rbenv Global

As its name suggests, this sets the ‘global’ version of Ruby to use in the command line when no other version is specified. Let’s set the global Ruby version to the one we just installed like so:

$ rbenv global 2.5.1

Now all calls to Ruby from anywhere on the command line will be directed by rbenv to version 2.5.1. The global version setting is stored in the ~/.rbenv/version file.

Rbenv Local

This sets the Ruby version to be used in the current local folder where the command is run, and overrides the global setting. For example, let’s say you’re in ~/cool_ruby_project. If you run the following:

$ rbenv local 2.3.1

Then rbenv will create a file in this folder called .ruby-version which contains nothing but the text 2.3.1.

When you try to run a Ruby command in this folder, rbenv will first read this file to determine that Ruby 2.3.1 should be used instead of the global 2.5.1. If you haven’t installed version 2.3.1, rbenv will print an error stating that it’s not installed.

Rbenv Shell

This command sets the version for the current terminal session only, and overrides both the global and local settings. To set it:

$ rbenv shell 2.4.2

This sets the local terminal environment variable RBENV_VERSION to 2.4.2. To unset it (and return to the local or global setting):

$ rbenv shell --unset

After Selection

Okay, so we’ve installed rbenv and Ruby 2.5.1, but there’s one more thing we need to do to make it really useful: install bundler:

$ gem install bundler

Bundler is Ruby’s library package management system and indispensable to working with projects in Ruby. You’ll need it to install Ruby libraries called gems.

Most Ruby projects have a file called Gemfile. This file lists all the gems that the project needs in order to work. Bundler’s job is to read the contents of this file, resolve all the dependencies, and fetch and install the gems required by the project.

Each version of Ruby on your system will need its own installation of the bundler gem, so don’t forget to run gem install bundler after installing a new one!


This does seem like a lot of stuffing around just to use a language, but doing it this way will avoid a lot of headaches in the future. Rbenv allows you to have as many versions of Ruby installed as you need, and keeps them and their gems isolated from each other so your projects don’t step on each others toes. Trust me, it’s well worth the effort :)

More Helpful Things

$ rbenv versions # Lists every version of Ruby known to Rbenv installed on your system.
$ rbenv version # Prints the current active version of Ruby (useful for sanity checking).

For more useful commands and more advanced features, the rbenv documentation can be found here.