title: Run a shell command when a file is added
body: <p>I have a folder named images on my linux box. 
  This folder is connected to a website and the admin of the site has the ability to add pictures to this site. However, when a picture is added, I want a command to run resizing all of the pictures a directory.</p>
  
  <p>In short, I want to know how I can make the server run a specific command when a new file is added to a specific location. </p>