Bundler

Bundler is a dependency management tool for Ruby applications designed to ensure a consistent and reproducible environment by locking the exact versions of gems used in a project. It operates by reading a Gemfile, where a developer specifies the required gems and optional constraints, and producing a Gemfile.lock that records the resolved gem versions and their dependencies.

A project’s Gemfile may declare sources (typically a RubyGems registry), groups, and platform-specific requirements. Bundler resolves all dependencies, fetches the appropriate gem versions, and writes the results to Gemfile.lock. This lockfile guarantees that installations across different machines and times reproduce the same dependency graph, preventing "gem version hell" and related conflicts.

Common workflows center around a small set of commands. bundle install installs the gems specified and locked in Gemfile.lock. bundle update refreshes version constraints and updates Gemfile.lock accordingly. bundle exec runs a command in the context of the bundle, ensuring the correct gem versions are used. Bundler also offers features for deployment and isolation, such as deploying with a restricted set of gems or installing to a specific path. New dependencies can be added with bundler add, which updates both Gemfile and Gemfile.lock.

Bundler is the standard dependency manager in the Ruby ecosystem and is widely used in Ruby and Rails projects to manage libraries and their compatibility. It integrates with RubyGems, supports multiple environments, and helps maintain reproducible builds across development, continuous integration, and production environments.