powered by text files


iCal interactions

Apple was nice enough to provide a feature rich interface for the AddressBook, and so I started my investigations of iCal with high hopes. Alas, these were to be dashed, and in rather short order.

XCode documentation wasn’t enlightening, Apple’s web site was notably quiet … something was amiss.

This article by Rod Schmidt over at O’Reilly started to shine some light on matters. To quote some key pieces of the puzzle:

Apple doesn’t provide any APIs to read iCal’s data, but you can do it yourself.


All the data for iCal is stored in .ics files in \~/Library/Calendars. There is one .ics file for each calendar you have created.

Ah ha! A starting point. Now to be honest I don’t have much in my iCal calendars, as I tend to use Exchange for calendaring, so I put a few things in and then went hunting. To my confusion, no such folder. It had to be somewhere.

According to a range of posts, Apple was definitely storing iCal information in a standard format, and with Spotlight now requiring everything to be files, it had to be somewhere.

$ cd ~/Library
$ find . -name '*.ics'
./Application Support/iCal/Sources/711885EF-B88B-44AE-B63E-A1409474922D.calendar/corestorage.ics
./Application Support/iCal/Sources/C28120BF-AE28-49AE-8869-E6616428A12A.calendar/corestorage.ics

This didn’t look as promising, but at least the .ics files have been located. Ignoring the cache directory, the other directory names didn’t look particularly nice, but included in each of them is a trusty Info.plist file that includes some useful properties.

At this point, I think it is safe to assume that the underlying structures changed somewhat in Tiger (or earlier) from the simplistic store mentioned in the O’Reilly article. Nothing too tricky though, so it should be possible to check for either type of directory store and locate the appropriate files.

If anyone has further information on iCal file storage, either in terms of links or corrections to anything I’ve mentioned, please post to the comments.

The next step would be to be able to manipulate these files. If I can avoid it, I’d rather not write a RFC2445 parser. Fortunately, several people have beaten me to it. provides a simple interface into the calendar file, with a simple class that wraps the file. The directory and file loading needs a bit of messing around with for Tiger.

I was looking for a bit more and found it in iCalendar by Max M. The library is LGPL’d which doesn’t cause me issues, but may have implications if you are wanting it for commercial software. Installation was typical Python style, pain free.

After installation and changing to one of the directories which contain my .ics files, the following allowed me to read the calendar (.ics) file:

>>> from icalendar import *
>>> cal = Calendar.from_string(open('corestorage.ics','rb').read())
>>> cal
VCALENDAR({'CALSCALE': 'GREGORIAN', 'VERSION': '2.0', 'PRODID': '-//Apple Computer\\, Inc//iCal 2.0//EN'})
>>> for component in cal.walk():

The API provides a range of useful documentation and examples, with unit tests for all the features. These in themselves also provide useful code snippets for deriving usage. The API also supports creating and modifying .ics files.

My aim in all this is to be able to update the underlying data for iCal. Brief tests show that changing the .ics files while iCal is running doesn’t quite lead to user interface updates. On the bright side, the Index files seem to be re-generated on closing and opening iCal.

Further investigation of this should hopefully lead to some way of coaxing iCal into playing nicely. At the moment I suspect it may involve a bit of Applescript to drive the application into a refresh if required.

(Update: refer to comments for the insight I was missing. On Tiger, Sync Services does exactly what I’m wanting in terms of keeping a calendar in sync with my app. For earlier versions, I should be able to live with exporting a calendar file.)