Heroku and adding SSH keys (trouble installing heroku gem

I am new to programming and trying to understand this error. The error is really strange because I have already installed the heroku gem (using sudo and not using sudo). I am using OS X.

skline-mac:~ skline$ sudo heroku keys:add 
/Users/skline/.rvm/rubies/ruby-1.开发者_开发技巧9.2-p136/lib/ruby/site_ruby/1.9.1/rubygems.rb:861:in `report_activate_error': Could not find RubyGem heroku (>= 0) (Gem::LoadError)
    from /Users/skline/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/site_ruby/1.9.1/rubygems.rb:255:in `activate'
    from /Users/skline/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/site_ruby/1.9.1/rubygems.rb:1204:in `gem'
    from /Users/skline/.rvm/gems/ruby-1.9.2-p136@rails3tutorial/bin/heroku:18:in `<main>'

You're using rvm, so there's no need for sudo, either for gem install heroku or using the heroku gem. This should work without any use of sudo:

gem install heroku
heroku keys:add

If this does not work, try resetting the ownership on your .rvm directory to your own user account (because you used sudo at some point in the past):

sudo chown -R $USER:staff ~/.rvm