title: How to have Autohotkey 'listen' for a change to a file?
body: <p>I have a text file, lets call it <code>C:\to_run.txt</code>.  I'd like my Autohotkey script to 'listen' to this file in such a way that when it detects a change, it performs an action immediately based on the contents of the file, and then make the file blank again.</p>
  
  <p>I can handle the last parts, so really I'm asking for an efficient way to detect file changes?  I say efficient because my Autohotkey script is getting rather long and I don't want this listening function to hang up the rest of the script in any way.</p>