Differences between the commands gem and bundle

In the Ruby ecosystem, gem and bundle serve distinct but complementary roles in managing code libraries (known as gems). While gem is the primary interface for the RubyGems package manager, bundle is the command used for Bundler, a tool built on top of RubyGems to manage project-specific dependencies.

Core Differences at a Glance

Feature	gem (RubyGems)	bundle (Bundler)
Primary Goal	General package management (install/uninstall/search).	Project-specific dependency management.
Scope	System-wide: Installs gems for the entire Ruby environment.	Project-local: Manages exact versions needed for a specific app.
Config File	None (uses direct command arguments).	Uses a Gemfile to list and lock dependencies.
Installation	Built into Ruby (v1.9+).	Must be installed as a gem itself (via gem install bundler).

The gem Command: The Package Manager

The gem command interacts with the global Ruby environment. It is used for broad administrative tasks rather than managing a specific application's needs.

• Key Functions: Used to search, install, list, and uninstall libraries from https://rubygems.org.

• Common Commands:

  • gem install <gem_name>: Downloads and installs a library to your system.
  • gem list: Shows all gems currently installed in your global Ruby environment.
  • gem search <query>: Finds available libraries on remote servers.

• Limitation: It does not track which versions of a gem a specific project needs, often leading to "dependency hell" if different projects require conflicting versions of the same gem.

The bundle Command: The Dependency Manager

Bundler solves the version conflict problem by creating an isolated environment for each project. It ensures that every developer on a team uses the exact same gem versions.

• How It Works: It reads a Gemfile, resolves all dependencies, and creates a Gemfile.lock to record the specific versions used.

• Key Functions:

  • bundle install: Reads the Gemfile, resolves dependencies, and installs missing gems.
  • bundle exec <command>: Runs a script (like jekyll or rake) specifically using the gem versions defined in the project's lock file.
  • bundle update: Updates gems to the latest allowed versions and updates the lock file.

• Consistency: It guarantees that the development, staging, and production environments are identical, preventing "it works on my machine" bugs.

When to Use Which?

• Use gem when you want to install a general-purpose tool on your computer, like a Ruby version manager or Bundler itself.
• Use bundle for almost everything related to your actual application code, such as adding new libraries to your project or running project-specific tasks.