bundler

groups

http://bundler.io/groups.html

gems outside any named group are in default group.

install gems from all groups:

$ bundle

install gems from all groups except production:

$ bundle --without production

if your app is gem dependent gems are added to gemspec file instead of Gemfile using add_runtime_dependency (kind of default group) or add_development_dependency (kind of development group) methods. these dependencies are then included in Gemfile using gemspec directive. in this case Gemfile might contain only test or custom groups.

require

http://bundler.io/groups.html

require all gems from groups default and production:

Bundler.require(:default, :production)

Rails app by default requires default and group corresponding to current environment in config/application.rb:

# Rails.groups = [:default, Rails.env]
Bundler.require(*Rails.groups)

in plain Ruby app you have 2 options:

• require all gems from all or selected groups in lib/my_app.rb (common entry point of CLI application or gem)

  # require gems from all groups
  Bundler.require
  # require gems from default and production groups
  Bundler.require(:default, :production)
  

  current environment can be fetched from custom environment variable - you’ve got to set it manually when launching app.

  this method is recommended for large Gemfiles.

• require gems manually in appropriate files where they are used

  • gems from test group (say, rspec) are required in spec/spec_helper.rb
  • gems which are used in Rakefile only (say, rubocop) are required only there
  • pry-byebug gem can be required in lib/my_app.rb only if DEBUG environment variable is set

  this method is recommended for smaller Gemfiles.

setup

http://bundler.io/bundler_setup.html

bundler setup configures the load path so that gems from all or specified groups can be required.

• configure the load path for all gems:

  require 'bundler/setup'
  

• configure the load paths for gems from specified groups:

  Bundler.setup(:default, :development)
  

• in theory you should first configure the load path and then require gems:

  require 'bundler/setup'
  Bundler.require
  

  but in practice I don’t configure the load path as described above - all gems can be required without configuring the load path first.

  UPDATE: I encountered situations when gem cannot be loaded because it’s not found without calling require 'bundler/setup' first - this is the case for ruby-fifo gem and my own gem files. thus I had to configure the load path before requiring gems by adding require 'bundler/setup' to the beginning of lib/my_app.rb file.