title: How to cp file only if it does not exist, throw error otherwise?
body: <pre><code>aws s3 cp "dist/myfile" "s3://my-bucket/production/myfile"
  </code></pre>
  
  <p>It always copies <code>myfile</code> to s3 - I would like to copy file ONLY if it does no exist, throw error otherwise. How I can do it? Or at least how I can use awscli to check if file exists?</p>