Ruby Hacking Guide
by Minero Aoki
The RHG is a book that explains how the ruby interpreter (the official C implementation of the Ruby language) works internally. To fully understand it, you need a good knowledge of C and Ruby. This book is going to investigate ruby as a whole.
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This book is a great collection of ideas, tricks, and skills that could be useful for Hackers. It's a unique extraction reference, summarizes a lot of research and experience. Rubyfu is a book to use not only to read, it's where ruby goes evil.
by Mark Slagell
Ruby is an easy object oriented language: it is designed to be easily read and written. This User's Guide will get you started at invoking and using ruby, and give you insights into ruby's nature that you may not get from the reference manual.
by Gregory T. Brown - O'Reilly Media
Ruby Best Practices aims to help Ruby developers from a wide range of skill levels improve their fundamental understanding of the language via exposure to the common practices and idioms that many seasoned Rubyists take for granted.
by Huw Collingbourne - Dark Neon Ltd.
A straightforward introduction to the fundamentals of Ruby programming: strings, numbers, objects, methods, class hierarchies, arrays, iterators, hashes, modules, mixins and much more. Small, self-contained programming samples are included.