title: Get timestamp including milliseconds
body: <p>I use this command a lot on OS X to create a timestamp for archiving purposes:</p>
  
  <pre><code>date -n +%Y%m%d%H%M%S
  </code></pre>
  
  <p>This gives an answer in this format:</p>
  
  <pre><code>20130625230005
  </code></pre>
  
  <p>I'd like to add milliseconds to the end of this string. Is it possible to get that with Ruby from the command line?</p>
  
  <p>It's unfortunately not possible to do this on OS X by adding something to the command above: <a href="https://stackoverflow.com/questions/17307086/add-milliseconds-to-timestamp-bash-unix">Add milliseconds to timestamp (bash, unix)</a> </p>