The AppFog command-line tool is packaged as a Ruby software package, known as a "Gem". If you are already using Ruby, simply install the Gem named af.
If you're not familiar with Ruby, refer to Appendix A, which contains instructions for installing Ruby and the AppFog Gem on common platforms.
To verify that the Gem is installed, enter the following command:
$ af version af 0.3.16.5
You will see af followed by your version number. See Chapter 5, Command-line Reference for details on all the command-line options.