Ruby, Gem, Bundler

What are Ruby, Gem, Bundler?

Think of the Ruby world as three stacked Lego bricks:

• Ruby itself – the language runtime (the “engine”).
• Gem – Ruby’s single-library package manager (one brick at a time).
• Bundler – the project-level multi-library resolver (the whole Lego set for one project).

Below is the long-form tour.

Ruby

An interpreted, object-oriented scripting language (like Python, Perl, Lua). Ships with a small standard library (File, Net::HTTP, JSON, etc.). Anything not in the standard library has to be installed separately → enter “gems”.

Gem

A gem is a plain *.gem file: code + metadata (name, version, author, dependencies).
gem install rails downloads the rails gem and its dependencies.

• To install into the user local directory(~/.local/share/gem/ruby/3.4.0/gems), use gem install.
• To install into the system wide direcotry(/usr/lib/ruby/gems/3.4.0/gems), use gem --no-user-install install bundler.

NOTE: You can check environment variables related to Gem by gem env.

Bundler (bundle, bundler)

Bundler is itself a gem (can be installed by gem install bundler).
It adds a project layer: every project gets its own Gemfile that declares exact gems + versions it needs.
Running bundle install:
– computes a full dependency graph, – writes the exact snapshot to Gemfile.lock, – downloads missing gems, – can optionally keep them inside the project (vendor/bundle) or in a shared path by bundle config set --local path 'vendor/bundle'

Typical workflow

1. Install ruby & bundler

   ruby -v                    # make sure Ruby is installed
   gem install bundler        # one-time global install
   

2. Edit Gemfile

bundle init                # creates an empty Gemfile

bundle init will create an empty Gemfile.

source 'https://rubygems.org'
gem 'jekyll', '~> 4.3'
gem 'rake',   '~> 13.0'

1. Install Gems

bundle install             # resolves & installs

bundle install will resolve depedencies and create gems.

Locked gems will be written in Gemfile.lock.

1. Run with locked gems

bundle exec jekyll serve   # run with locked gems