Resources to learn ruby for use in logstash

Looking for a path to knowledge.... I don't know Ruby, but if I study a "Ruby for Dummies" type book, it probably won't have any specifics for logstash and will probably teach things never used in logstash. I think I'm looking for something that explains the logstash "schema" or data dictionary in the Ruby environment, maybe with examples.

Any suggestions?

I have also not come across such document. it would be good to have.
Everything I have learn about ruby is from this forum. either search or by asking questions.