解决ri Nothing known about问题

例如：

$ ri File
Nothing known about File

 解决方法：

First select a RVM ruby.

$ rvm use 1.9.2

Next generate the core ruby documentation.

$ rvm docs generate

And finally open the core ruby documentation in your local web browser. Note that for this to work either `open` or `xdg-open` must be found in your system.

$ rvm docs open

 

 

源自:http://beginrescueend.com/rubies/docs/