Ruby User's Guide
by Mark Slagell
Number of pages: 264
Ruby is "an easy object oriented language". It may seem a little strange at first, but 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.
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Everything from installing Ruby and the basics of the language through to topics such as arrays, file handling and object-oriented programming are covered. Written both for experienced in other programming languages and for novices.
by why the lucky stiff
This is just a small illustrated online-only Ruby book. It won't crush you. It's light as a feather (because I haven't finished it yet--hehe). And there's a reason this book will stay light: because Ruby is simple to learn.
RubyGems is the premier ruby packaging system. It provides: A standard format for distributing Ruby programs and libraries; An tool for managing the installation of gem packages; A gem server utility for serving gems from any machine...
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.