ri1.9.1 1.9.1.378-1 (amd64 binary) in ubuntu lucid

 ri is a command line tool that displays descriptions of built-in Ruby
 methods, classes, and modules. For methods, it shows you the calling
 sequence and a description. For classes and modules, it shows a
 synopsis along with a list of the methods the class or module
 implements.
 .
 This package provides ri command and descriptions about Ruby 1.9.1.