When developing a RubyGem, it is often helpful to launch an IRB console preloaded with your library. There are a few ways you can do this.

First you can call IRB directly with the path to your gem:

# If using bundler
bundle exec irb -r./lib/my_gem.rb

# Without
irb -r./lib/my_gem.rb

This works great, and before Bundler, I always shipped a rake console task that ran a similar command.

If you are using Bundler you can do this easier with the bundle console command. Behind the scenes it does pretty much the same thing, but it also sets up Bundler so you have access to dependencies.

For most purposes, bundle console is all you need. However, if you need to add some custom behavior, such as console-only methods, you will need to script this yourself.

I do this in some private projects to make it easier for debugging. For example, I am working on a CLI script that connects to multiple databases depending on the arguments given. In production this never happens at the same time. In development though, it is pretty useful to access multiple databases at once. Instead of copying and pasting the connection commands every time, I can package this in a console script.

In another project, there are some convenience methods that make it easier to work with the library in the console, but aren’t necessarily something that makes sense as a public API.

To illustrate, lets assume you have a gem called MyGem (using Bundler).

Create a file lib/my_gem/console.rb that contains the following:

require "bundler/setup"
require "my_gem"
require "irb"

puts "Loading MyGem"

# Connect to the DBs
MyGem.connect_to_db :one
MyGem.connect_to_db :two

# This method will be available in the console
def say_hello
  puts "Say hello"


Next create a file in script/console:

require File.expand_path("../../lib/my_gem/console", __FILE__)

Now when you want to run MyGem in the console, simply run ./script/console and it will require the library, connect to the DBs, and define the say_hello.