title: Conditional ARG in Dockerfile?
body: <p>I'm trying to conditionally install vim in my docker container if I pass an optional ARG - say something like DEVBUILD. I can't find any documentation on how to use something like IF in a Dockerfile. Something like this:</p>
  
  <pre><code>FROM node:8
  if $DEVBUILD {
      RUN apt-get update
      RUN apt-get --assume-yes install vim
  }
  </code></pre>
  
  <p>Is this possible, and if so, where can find a reference on the syntax?</p>