ri1.8 1.8.7.174-1 (amd64 binary) in ubuntu karmic

 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 1.8.