title: How exactly do you use variables in Jenkins?
body: <p>Can someone concisely explain what the differences between the three variables below are? Because in all honesty, when I create a Jenkins job, I randomly guess between the three types until something works, but I'd love to understand rather than blindly picking.</p>
  
  <pre><code>${ENV,var="BUILD_USER"}
  ${BUILD_USER}
  $BUILD_USER
  </code></pre>
  
  <p>Also, are there other ways of writing variables in Jenkins that I missed other than the 3 ways above?</p>