in ~/.bash_profile add the following line
export PATH=/usr/local/Cellar/ruby/1.9.3-p194/bin:$PATH
When you’re done, close your terminal and re-open it. You should be fine.
Alternatively, you can execute the follwing in each open shell instead of closing/re-opening:
source ~/.bash_profile
Note:
I highly recommend installing ruby via rvm or rbenv so you can manage multiple ruby versions and use gemsets.