title: Git: check whether file exists in some version
body: <p>In my application, I'm using git for version management of some external files</p>
  
  <p>I'm using commands like <code>git show HEAD~1:some_file</code> to get a certain version (based on git tag, commit hash or relation to HEAD) of a file.
  When the file does not exist, a 'fatal' message is outputted (I think to the stderr pipe).
  e.g.</p>
  
  <blockquote>
    <p>fatal: Path 'some_file' does not exist in 'HEAD~1'</p>
  </blockquote>
  
  <p>Is there a clean command to check whether a file exists in a certain version?</p>