Replacing cron with iCal

cron is deprecated in OS X. iCal makes a straightforward, if tedious, replacement, despite its limited support for scripted alarms.

In iCal you can easily create a repeating event with an associated alarm that runs a script.


Put all of your periodic system management events into a hidden "Automation" calendar (so they don't clutter up the calendar view) and you're all set.


Of course, there's a problem. I prefer to write system management scripts using Python. iCal can run only AppleScripts.

It's easy to write an AppleScript "wrapper" which just launches a shell script, but the process involves lots of button-clicking:
  • Launch Script Editor
  • Enter do shell script "/path/to/shell/script"
  • Save the script
  • Quit Script Editor
Luckily, the osacompile command lets you do the same thing from the command line. Together with Python's pathname-manipulation facilities, osacompile makes it simple to create AppleScript wrappers for shell scripts.

Given the path to a shell script, the following Python program creates a corresponding AppleScript wrapper in the same directory:
#!/usr/bin/env python
import sys, os, subprocess, logging
def main():
for filename in sys.argv[1:]:
pathname = os.path.abspath(filename)
scriptname = os.path.splitext(pathname)[0] + ".scpt"
if os.path.exists(scriptname):
status = subprocess.call([
"-e", 'do shell script "%s"' % pathname,
"-o", scriptname])
if status:
logging.error("Got status %d creating %s" %
(status, scriptname))

if __name__ == "__main__":


Andrew Marlow said...

It's a bit Apple-centric. I agree that ical is better than cron. The trouble is, there does not appear to be a general-purpose ical daemon that corresponds to the cron daemon.

Andrew Marlow said...

I have just come across ical. I am a UNIX guy, not an Apple guy. For UNIX people, cron is supposed to be the answer to how to schedule jobs, but I reckon that the ical format is better. So I am trying to track down any open source implementation of an ical daemon, similar to the cron daemon. The closest I have come is the libical C API for interpreting ical schedules. I wonder if anyone can help please?

Mitch said...

I prefer cron as well. Were it not deprecated under OS X, in favor of the comparatively hard-to-use launchctl, I wouldn't have been considering ical.

Regarding open-source ical daemons, see http://caldav.calconnect.org/implementations.html .

Thanks for reading!