Learn Ruby in ten pages

I have a little spare time (business is slow), so I am learning Ruby. There are really good reasons to do so:

• Ruby is the cleanest object-oriented language I have encountered. Everything is an object, and all objects are accessible to me as a coder. I can add code to any class, and override its methods with or without using inheritance. I never have to worry about whether this or that identifier might be  something "special" that needs to be treated differently or managed with care.
• Ruby is spare, elegant, and aesthetic. While I haven't worked with it much yet, I think the language's design will help me write concise, lucid code.
• Ruby on Rails and its variants are sweeping the field in terms of web frameworks. I have seen complex, highly interactive sites produced and maintained easily by small startups using Rails.

Ruby is a reasonably small language. I've been taking notes as I go through various tutorials and bits of documentation, an I'm going to publish my notes as posts. I believe the entire Ruby language can be summarized in about ten posts. 

If you see a mistake, or if something is unclear, please let me know. I am a beginner at Ruby, and my purpose is to learn Ruby.

The pages will be:

• Keywords, Identifiers, and simple data types
• Strings and Arrays
• Hashes and Ranges
• Classes and objects
• Modules
• Code blocks
• Exceptions
• Practical matters: Files, logging, time, serialization, random numbers, command-line arguments, environment

That's only eight - I expect to need to split one or two of them, so I can keep reasonable page sizes while sticking to my original limit.

As I complete my notes on each topic I'll link to it from this post.