Ruby Gems & Bundler Cheat Sheet

Covers RubyGems CLI commands, Gemfile syntax, Bundler workflows, and semantic version constraint operators for managing dependencies.

1 PageBeginnerMar 25, 2026

gem CLI

Managing individual gems directly with RubyGems.

bash

gem install rails               # Install a gem globallygem list                        # List installed gemsgem uninstall rails              # Remove a gemgem search rails                 # Search RubyGems.orggem build mygem.gemspec          # Build a gem packagegem push mygem-1.0.0.gem         # Publish to RubyGems.org

Gemfile Syntax

Declaring dependencies and environment-specific groups.

ruby

# Gemfilesource "https://rubygems.org"ruby "3.2.2"gem "rails", "~> 7.1.0"gem "pg", ">= 1.4"gem "puma"group :development, :test do  gem "rspec-rails"  gem "pry"endgroup :production do  gem "redis"endgem "rack-cors", git: "https://github.com/cyu/rack-cors.git", branch: "main"

Bundler CLI

Installing and running gems with locked versions.

bash

bundle install               # Install gems from Gemfile, write Gemfile.lockbundle update                 # Update all gems to latest allowed versionsbundle update rails           # Update just one gembundle exec rspec             # Run a command using bundled gem versionsbundle exec rails serverbundle check                  # Verify all gems are installedbundle add sidekiq             # Add a gem to Gemfile and install it

Version Constraints

How Bundler interprets common version operators.

~> 7.1.0- Pessimistic constraint: allows patch updates only, equivalent to >= 7.1.0 and < 7.2.0
~> 7.1- Allows minor and patch updates, equivalent to >= 7.1 and < 8.0
>= 1.4- Any version 1.4 or newer, including major version bumps
Gemfile.lock- Records the exact resolved versions; commit it to ensure identical installs across environments
bundle exec- Runs a command in the context of the Gemfile's locked gem versions, avoiding conflicts with system gems
group blocks- Scope gems to environments (development/test/production) so bundle install --without can skip them

Pro Tip

Commit Gemfile.lock for applications (not for gems you're publishing) so every environment, including CI and production, resolves the exact same dependency versions.

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