Retrieves the outward facing IP address from your Airport Extreme
router, and if it has changed, tell freedns.afraid.org.

By checking your router, it avoids generating any internet traffic
and freedns.afraid.org activity unless your IP address changes.

This script has only been tested on MacOS X Lion (10.7) and
Mavericks (10.9) with an Airport Extreme.  If you have any
suggestions on making the script more portable or robust, please
let me know.


Directions:
  0) Adjust PATH if necessary.  No need for MacOS X.

  1) Create a text file "$HOME/.afraid-dyndns.dynkey" and add one line
     to it with your dynamic authentication token from
     http://freedns.afraid.org/dynamic/ .

  2) Create a text file "$HOME/.afraid-dyndns.email" and add one line
     to it with a comma separated list of the email addresses to
     notify when the IP address changes.  This file is optional if you
     do not want to be notified via email.

  3) Add an entry to your crontab to run this script periodically.
     Script can run as you.  It does not require any privileges to run.