title: print ARG value in docker build
body: <p>Is there a way to print <code>ARG</code>s values, that are passed via the <code>--build-arg</code> flags to a <code>docker build</code> command?</p>
  
  <p>Just using <code>RUN echo $ARG_NAME</code> isn't enough since I want it to be printed before the <code>FROM</code> section, where it's not allowed.</p>
  
  <p>The point is to see these values immediately so I can stop the build quickly, preventing downloading the wrong base images.</p>
  
  <p>Already searched docker docs and google. Maybe someone here can shed some light.</p>