title: How to pass user defined parameters to rpmbuild to fill variables
body: <p>is it possible to pass parameters to rpmbuild to fill user defined variables that are called inside the spec file?</p>
  
  <p>Example: 
  The user defined variable %{foobar} which is called in the .spec file (but empty) should be filled with the variable which is passed when executing the rpmbuild command</p>
  
  <pre><code>rpmbuild -bb --foobar="Foo" somespecfile.spec
  </code></pre>