Use cron in OSX
First create a .crontab file in your home directory. This is your per-user cron config, here is an example:
* * * * */5 ~/scripts/rysnc.rb
(In the example above, rysnc.rb is executeable. I prefer ruby for complex operations.)
For OSX to load your cron config, execute:
Whenever you updated the crontab file, execute the command above to update the system.
You can see the system loaded config with:
sudo cat /usr/lib/cron/tabs/$USER