125 Gems, bundler, rbenv [1d]

Posted Almost 8 years ago. Visible to the public.

makandra is responsible for maintaining about 75 Ruby projects. These projects use a large number of different versions for Ruby, Rails and many gems. To be able to switch between projects easily, we must control every dependency our applications has.


  • Understand what a gem is
  • Learn how to install a gem
  • Be able to look into gem code
    • locally
    • on GitHub
  • Learn about Bundler
    • Why is it necessary:
      • Managing versions and dependencies
      • Defining a consistent project environment
    • What is the difference between bundle install and bundle update?
    • What does bundle exec do, why is it necessary?
    • What does the file Gemfile.lock do?
  • rbenv
    • Understand why we need rbenv



Working with rbenv

  • Use rbenv to install an older Ruby version, like 2.5.
  • In an earlier lesson you built a searchable address book.
  • Freeze that program's Ruby version to 2.5 by adding an .ruby-version file.
  • Open a new terminal and check your default Ruby version (ruby -v)
  • Now cd into the directory for the address book app. Observe how rbenv has automatically switched to the Ruby version from your .ruby-version.
  • Commit and push your changes.


RubyMine seems to only parse the .ruby-version file when you're opening a project for the first time. When you're changing the .ruby-version of an existing project, RubyMine may not automatically detect that you want to use another version.

If this is the case, go to File / Settings / Languages & Frameworks / Ruby SDK & Gems and select the new Ruby version.

Working with Bundler

  • In an earlier lesson you built a searchable address book.
  • Add a Gemfile to that repository and let bundler create a Gemfile.lock. It won't have any dependencies at first.
  • Commit the Gemfile and Gemfile.lock.
  • Use Bundler to install the Faker Show archive.org snapshot gem in the exact version 2.10.0.
  • Observe the changes Bundler made to your Gemfile.lock. Compare these changes to faker's dependencies on rubygems.org Show archive.org snapshot .
  • In your program, use Faker to create 100 contacts with fake data.
  • Commit your changes.
  • Use Bundler to upgrade Faker to the latest possible version that runs with Ruby 2.5.
  • Observe the changes Bundler made to your Gemfile.lock during the upgrade.
  • Commit and push your changes.

How gems are made

Henning Koch
Last edit
9 months ago
Michael Leimst├Ądtner
Source code in this card is licensed under the MIT License.
Posted by Henning Koch to makandra Curriculum (2015-07-07 14:59)