Installing Ruby and Using IRB

Before writing any Ruby code, you need a working Ruby installation and a way to experiment quickly. Most developers install Ruby through a version manager rather than a system package manager, because Ruby projects frequently pin specific versions, and a version manager lets you switch between them without conflicts. Once Ruby is installed, IRB (Interactive Ruby), Ruby's built-in read-eval-print loop (REPL), lets you type expressions and see results immediately, making it an essential tool for learning the language and debugging small snippets.

The two most common Ruby version managers are rbenv and RVM. rbenv is lightweight and does one thing well: it manages which Ruby version is active per shell or per directory, delegating actual installation to the ruby-build plugin. RVM is older and more feature-rich, also managing gemsets, but is heavier. A newer, faster option gaining popularity is mise (formerly rtx), which manages multiple language runtimes including Ruby. Whichever you choose, avoid relying solely on the OS-bundled Ruby, since it is often outdated and modifying it can break system tools that depend on it.

IRB evaluates each line you enter and prints its return value, prefixed with =>. This makes it ideal for testing method behavior, exploring an unfamiliar object's API, or checking how a piece of syntax parses. You can inspect an object's available methods with .methods, check its class with .class, and load an external file with load or require_relative. Modern Ruby (3.0+) ships an improved IRB with multiline editing, autocomplete, and colorized output, making it far more pleasant than earlier versions.