title: list all the files from s3 using aws-sdk gem
body: <p>I have a following scenario.
  Consider in my case <strong>aws s3 folder structure</strong> is as follows</p>
  
  <pre><code>- videos
    - my_videos
      - college
  </code></pre>
  
  <p>I have uploaded video file say <code>myfirst_day.mp4</code> in the <code>college</code>, for this related formed key is <code>"videos/my_videos/college/myfirst_day.mp4"</code></p>
  
  <p>Now I have to list all the files from the <code>videos/my_videos/college</code> directory.
  How can I do it.</p>
  
  <p>For this I am using <strong>aws-sdk gem</strong></p>