title: Use expressions instead of variables in azure devops
body: <p>In azure devops, inside the classic build, I can generally do <code>$(myVar)</code> to get the value of a variable in certain places. I am not sure if that particular usage has a name. </p>
  
  <p>Is there a way to pass an expression for the same use cases. I mean instead of <code>$(myVar)</code> can I do something like <code>$(coalesce(myVar, otherVar))</code>? 
  I have tried wrapping it in different brackets, doesn't seem to work. </p>
  
  <p>I have checked the docs here: <a href="https://docs.microsoft.com/en-us/azure/devops/pipelines/process/expressions?view=azure-devops" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/azure/devops/pipelines/process/expressions?view=azure-devops</a></p>
  
  <p>It doesn't show how to use in the classic pipelines, only yaml. </p>