Ruby References

By Xah Lee. Date: 2012-12-08. Last updated: 2016-02-11.

hummingbird book ruby programming language 64527 — The Ruby Programming Language 2008-02-01 By David Flanagan. Buy at amazon

This is the best.

By the same guy who wrote JavaScript the Definitive Guide. 〔see JavaScript Book by David Flanagan, and the Man-made Complexity in Computer Language〕