title: Total size of the contents of all the files in a directory
body: <p>When I use <code>ls</code> or <code>du</code>, I get the amount of disk space each file is occupying. </p>
  
  <p>I need the sum total of all the data in files and subdirectories I would get if I opened each file and counted the bytes. Bonus points if I can get this without opening each file and counting.</p>