Ruby comes with a random number generator. The method to get a randomly chosen number is rand. If you call rand, you'll get a float greater than or equal to 0.0 and less than 1.0. If you give it an integer parameter (by calling rand(5) ), you will get an integer value greater than or equal to 0 and less than 5.
Here's an example: p026phrase.rb
The above program makes three lists of words, and then randomly picks one word from each of the three lists and prints out the result.
Note: The Ruby Logo is Copyright (c) 2006, Yukihiro Matsumoto. I have made extensive references to information, related to Ruby, available in the public domain (wikis and the blogs, articles of various Ruby Gurus), my acknowledgment and thanks to all of them. Much of the material on rubylearning.com and in the course at rubylearning.org is drawn primarily from the Programming Ruby book, available from The Pragmatic Bookshelf.