Something about Homebrew install ruby

I installed the ruby1.8.7 by macports.
Yesterday, I updated the ruby into 1.9.1 by homebrew.
But when I show the version (ruby -v),It still is 1.8.7. So I use brew link ruby,and replace the /opt/local/bin/ruby by /usr/local/Cellar/ruby/1.9.1-p378/bin/ruby. It works. But command "ri" is not work yet.

Is there any way to use the ruby installed by homebrew?

,sorry for my english