# Installing Ruby, irb, Gems and Bundler — Ruby

Source: https://www.geekswithgeeks.com/en/ruby/f-setup

> Install Ruby with a version manager and manage dependencies with Bundler.

## Tools of the trade

Install Ruby with a **version manager** so each project can use the version it needs: **rbenv**, **chruby** with ruby-install, **asdf** or **mise** on macOS and Linux, and RubyInstaller on Windows. A `.ruby-version` file in a project records its version. **`irb`** (Interactive Ruby) is the REPL for experimenting, with syntax highlighting and autocompletion in recent versions. Libraries are packaged as **gems** and published on **RubyGems.org**. **Bundler** manages a project's dependencies: the **`Gemfile`** lists gems with version constraints (the pessimistic operator `~> 7.2` allows 7.x updates from 7.2 but not 8.0), `bundle install` resolves and installs them, **`Gemfile.lock`** pins exact versions (commit it for applications), and **`bundle exec`** runs commands with exactly those versions. `bundle add <gem>` adds a dependency. Use `ri` or the online documentation at ruby-doc.org for core classes. Editors such as VS Code with the **Ruby LSP** extension, or RubyMine, provide completion, navigation and debugging.

## A project with Bundler

Gemfile declares dependencies; bundle exec uses the locked versions.

```bash
mise use ruby@3.4          # or: rbenv install 3.4.x && rbenv local 3.4.x
ruby -v

mkdir invoice_tool && cd invoice_tool
bundle init                 # creates a Gemfile
bundle add csv
bundle add rspec --group test

# Gemfile
# source "https://rubygems.org"
# ruby "~> 3.4"
# gem "csv"
# group :test do
#   gem "rspec", "~> 3.13"
# end

bundle install              # writes Gemfile.lock
bundle exec rspec           # run tools with the locked gem versions
irb                         # interactive experiments
```

## A shopping list and a receipt

The Gemfile is your shopping list ("some rspec, version 3.something"); Gemfile.lock is the receipt with the exact versions bought. `bundle exec` makes sure you cook with what is on the receipt, not whatever happens to be in the cupboard.

**Quiz:** What does bundle exec do?

- [ ] Installs Ruby
- [ ] Publishes a gem
- [ ] Formats code
- [x] Runs a command using exactly the gem versions recorded in Gemfile.lock

*Answer:* Runs a command using exactly the gem versions recorded in Gemfile.lock. bundle exec ensures the locked dependency versions are used.