title: Bash script to delete all but N files when sorted alphabetically
body: <p>It's hard to explain in the title.</p>
  
  <p>I have a bash script that runs daily to backup one folder into a zip file. The zip files are named <strong>world</strong><code>YYYYMMDD</code><strong>.zip</strong> with <code>YYYYMMDD</code> being the date of backup. What I want to do is delete all but the 5 most recent backups. Sorting the files alphabetically will list the oldest ones first, so I basically need to delete all but the last 5 files when sorted in alphabetical order.</p>