Direct dependencies

gem "rails", "~> 7.1" gem "pg", ">= 1.0" gem "puma"


### Version Constraints

```ruby
# Exact version
gem "rails", "7.1.0"

# Minimum version
gem "pg", ">= 1.0"

# Pessimistic constraint (recommended)
gem "rails", "~> 7.1"      # >= 7.1.0, < 8.0
gem "rails", "~> 7.1.0"    # >= 7.1.0, < 7.2.0
gem "rails", "~> 7.1.2.3"  # >= 7.1.2.3, < 7.1.3.0

# Combined constraints
gem "nokogiri", ">= 1.12", "< 2.0"

# Any version (not recommended)
gem "puma"

Gem Groups

# Default group (always installed)
gem "rails"

# Named groups
group :development do
  gem "better_errors"
  gem "binding_of_caller"
end

group :test do
  gem "rspec-rails"
  gem "capybara"
end

group :development, :test do
  gem "factory_bot_rails"
  gem "faker"
end

group :production do
  gem "redis"
end

Install Without Groups

# Skip groups during install
bundle config set --local without development test
bundle install

# Or inline
bundle install --without development test

Gem Sources

Alternative Sources

source "https://rubygems.org"

# Private gem server
source "https://gems.example.com" do
  gem "private_gem"
end

Git Repositories

# From GitHub (shorthand)
gem "rails", github: "rails/rails"
gem "rails", github: "rails/rails", branch: "main"
gem "rails", github: "rails/rails", tag: "v7.1.0"
gem "rails", github: "rails/rails", ref: "abc123"

# Full git URL
gem "my_gem", git: "https://github.com/user/my_gem.git"
gem "my_gem", git: "git@github.com:user/my_gem.git"

# Specific subdirectory
gem "my_gem", github: "user/monorepo", glob: "gems/my_gem/*.gemspec"

Local Path

# For development
gem "my_gem", path: "../my_gem"
gem "my_gem", path: "~/projects/my_gem"

Platforms and Requirements

Platform-Specific Gems

# Only on specific platforms
gem "bcrypt", platforms: :ruby
gem "wdm", platforms: :mswin

# Exclude platforms
gem "sqlite3", platforms: [:ruby, :mswin]

# Common platforms:
# :ruby - C Ruby (MRI), Rubinius
# :mri - Only MRI
# :jruby - JRuby
# :mswin - Windows
# :mingw - MinGW
# :x64_mingw - 64-bit MinGW

Ruby Version Requirements

# In Gemfile
ruby "3.2.0"

# With engine
ruby "3.2.0", engine: "jruby", engine_version: "9.4.0"

# Version constraint
ruby "~> 3.2.0"

Lock File

Understanding Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    actionpack (7.1.0)
      actionview (= 7.1.0)
      activesupport (= 7.1.0)
      rack (~> 2.2)

PLATFORMS
  arm64-darwin-22
  x86_64-linux

DEPENDENCIES
  rails (~> 7.1)

RUBY VERSION
   ruby 3.2.0p0

BUNDLED WITH
   2.4.0

Managing Platforms

# Add platform
bundle lock --add-platform x86_64-linux arm64-darwin

# Remove platform
bundle lock --remove-platform x86_64-linux

# Update lock file for all platforms
bundle lock --update

Common Commands

Install and Update

# Install gems from Gemfile.lock
bundle install

# Update all gems
bundle update

# Update specific gems
bundle update rails pg

# Conservative update (minimal changes)
bundle update --conservative rails

# Update only patch versions
bundle update --patch

# Update minor versions
bundle update --minor

Dependency Information

# Show gem info
bundle info rails

# Show dependency tree
bundle show

# List all gems
bundle list

# Show outdated gems
bundle outdated

# Check for security issues
bundle audit

Execution

# Run command with bundled gems
bundle exec rails server
bundle exec rspec

# Create binstubs
bundle binstubs rspec-core
bin/rspec  # Faster than bundle exec

# Open gem in editor
EDITOR=code bundle open rails

Configuration

Bundle Config

# Set configuration
bundle config set --local path vendor/bundle
bundle config set --local without development test

# View configuration
bundle config list

# Unset configuration
bundle config unset path

Common Settings

# Install gems locally (not system-wide)
bundle config set --local path vendor/bundle

# Parallel installation
bundle config set --local jobs 4

# Disable shared gems
bundle config set --local disable_shared_gems true

# Use system gems
bundle config set --local system true

Configuration File

# .bundle/config
---
BUNDLE_PATH: "vendor/bundle"
BUNDLE_WITHOUT: "development:test"
BUNDLE_JOBS: "4"

Troubleshooting

Common Issues

# Clear cache and reinstall
rm -rf vendor/bundle .bundle Gemfile.lock
bundle install

# Reinstall all gems
bundle install --redownload

# Debug resolution
bundle install --verbose

# Check for conflicts
bundle check

Version Conflicts

# Error: Bundler could not find compatible versions

# Solutions:
# 1. Update the conflicting gem
bundle update conflicting_gem

# 2. Relax version constraints
# Change "~> 1.0.0" to "~> 1.0"

# 3. Check dependency tree
bundle viz  # Requires graphviz

Native Extensions

# If native extension fails
bundle config build.nokogiri --use-system-libraries
bundle install

# Provide library paths
bundle config build.pg --with-pg-config=/usr/local/bin/pg_config

Best Practices

Version Constraints

# Good: Pessimistic constraints allow updates
gem "rails", "~> 7.1"

# Avoid: Exact versions prevent updates
gem "rails", "7.1.0"

# Avoid: No constraint is risky
gem "rails"

Group Organization

# Keep groups focused
group :development do
  # Development tools only
end

group :test do
  # Testing tools only
end

group :development, :test do
  # Shared tools (factories, debugging)
end

Lock File Management

Always commit Gemfile.lock
Update lock file deliberately, not accidentally
Review changes to lock file in PRs
Periodically run bundle update to get security patches

CI/CD

# Fast CI install
bundle config set --local frozen true
bundle config set --local deployment true
bundle install --jobs 4 --retry 3

Gemfile.lock vs Gemfile

Gemfile	Gemfile.lock
Dependencies you want	Exact versions resolved
Version constraints	Specific versions
Human-edited	Machine-generated
Flexible	Deterministic
What you need	What you have

Always commit both files. The lock file ensures everyone uses identical gem versions.

bundler

Bundler Dependency Management

Gemfile Basics

Structure