Mac OS X crontab FAQ: How do I run a Unix job (or shell script) through the OS X crontab facility? I keep trying to edit my Mac crontab file, but my Mac OS X system won't save my crontab changes, or run my program (or shell script).
Mac OS X - crontab, launchd, and launchctl
As of this writing (updated in 2011), the Mac crontab command seems to be deprecated on Mac OS X, and the Apple documentation encourages you to use their "Mac launchd" facility. Here's a blurb from the Mac OS X crontab man page: