The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

21.4. The ri Utility

The ri is apparently named from “Ruby index” or some such mnemonic. It is a command-line documentation tool, offering information on Ruby classes, methods, modules, and so on. Here is an example:

$ ri each_with_index
--------------------------------------------------------
  enumObj.each_with_index {| obj, i | block }  -> nil
--------------------------------------------------------

  Calls block with two arguments, the item and its index,
  for each item in enumObj.

     hash = Hash.new
     %w(cat dog wombat).each_with_index {|item, index|
       hash[item] = index
     }
     hash   #=> {"dog"=>1, "wombat"=>2, "cat"=>0}

Note that it has a few bugs and quirks. You are encouraged to report these (along with typos and other inaccuracies) if you can find anyone ...