OS X comes with Ruby 1.8.7 preinstalled. This version is rapidly falling out of use by the Ruby development community, but it does support the AppFog Gem. If your sole use of Ruby is to work with AppFog, you don't need to install a later version of Ruby. If you do plan to do Ruby application development, consider installing RVM. See the section The Ruby Version Manager.
You'll use the
sudo command to install the AppFog Gem. This command requires that you have a non-blank administrator password. For more information, refer to Mac OS X: sudo command requires a non-blank admin password available at http://support.apple.com/kb/HT4103.
To install the AppFog Gem, open a Terminal window, and enter the following two commands:
sudo gem install af sudo gem install sinatra