Since Ruby 2.6

Bundler makes sure Ruby applications run the same code on every machine.

It does this by managing the gems that the application depends on. Given a list of gems, it can automatically download and install those gems, as well as any other gems needed by the gems that are listed. Before installing gems, it checks the versions of every gem to make sure that they are compatible, and can all be loaded at the same time. After the gems have been installed, Bundler can help you update some or all of them when new versions become available. Finally, it records the exact versions that have been installed, so that others can install the exact same gems.

An extensive documentation for Bundler, including guides, references and best practices, could be found at its site.

Getting Started

Getting started with bundler is easy! Since Ruby 2.6, Bundler is a part of Ruby’s standard library.

Specify your dependencies in a Gemfile in your project’s root:

source 'https://rubygems.org'
gem 'nokogiri'
gem 'rack', '~> 2.0.1'
gem 'rspec'

Learn More: Gemfiles.

Install all of the required gems from your specified sources:

$ bundle install
$ git add Gemfile Gemfile.lock

Learn More: bundle install.

The second command adds the Gemfile and Gemfile.lock to your repository. This ensures that other developers on your app, as well as your deployment environment, will all use the same third-party code that you are using now.

Inside your app, load up the bundled environment:

require 'rubygems'
require 'bundler/setup'

# require your gems as usual
require 'nokogiri'

Learn More: Bundler.setup.