Programming Ruby 1.9: The Pragmatic Programmers' Guide

Ruby is a fully object-oriented language, much like the classic object-oriented language, Smalltalk. Like Smalltalk, it is dynamically typed (as opposed to Java or C++), but unlike Smalltalk, Ruby features the same conveniences found in modern scripting languages, making Ruby a favorite tool of intelligent, forward-thinking programmers and the basis for the Rails web framework.
This is "the" reference manual for Ruby, including a description of all the standard library modules, a complete reference to all built-in classes and modules (including all the new and changed methods introduced by Ruby 1.9). It also includes all the new and changed syntax and semantics introduced since Ruby 1.8. Learn about the new parameter passing rules, local variable scoping in blocks, fibers, multinationalization, and the new block declaration syntax, among other exciting new features.