title: Adding command line options to CMake
body: <p>I'm building a large library using CMake, and I would like users to be able to selectively enable/disable certain parts of my build process.</p>
  
  <p>How can I add command-line options to my CMake build, e.g. so that users may type something like <code>cmake --build-partone --nobuild-parttwo --dothis=true --dothat=false ..</code>?</p>
  
  <p>Apparently the OPTION keyword will create variables that can be set from the CMake GUI, but I can't figure out how to do this from the command line.</p>