➜ ~ rvm -v rvm 1.10.2 by Wayne E. Seguin , Michal Papis [https://rvm.beginrescueend.com/] ➜ ~ ruby -v ru
Simone's answer is great. However, if you already have your Rails gem in your Gemfile, just try to use bundle exec instead:
bundle exec rails c
And that should suffice. If not, then add
bundle install
before the mentioned command.