How to skips holidays when creating reoccuring events?

Question

We're a school. And we use ical to keep track of class schedules. We have our classes twice a week and sometimes they fall on holidays. We have our class schedules set up in ical as "Reoccuring Events." How do you have reoccuring events skip holidays?

Answer 1

Although iCal's mechanism for creating recurring events does not support it, iCal itself respects the excluded dates option, if it finds it. So, one possibility would be to create the recurring event, then drag the first occurrence to the Desktop and delete it from iCal. Then use TextEdit (or similar) to add a line after the RRULE line for each excluded date (or put several dates on the one line, separated by commas). Drop the edited file back onto iCal.
A couple of cautions: don't just make a new line, or it upsets iCal - copy and paste and edit an existing one. The time portion of the excluded dates MUST match the time portion of the DTSTART, or iCal will quietly ignore it. In the example below, I have omitted the time zone info that will come before the VEVENT.
Before:
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Apple Inc.//iCal 4.0.4//EN
CALSCALE:GREGORIAN
BEGIN:VEVENT
CREATED:20110629T224702Z
UID:04BBAED9-F08C-46C6-BB06-6D1ECE382C40
DTEND;TZID=Europe/Dublin:20110630T113000
RRULE:FREQ=DAILY;INTERVAL=1;COUNT=10
TRANSP:OPAQUE
SUMMARY:Test
DTSTART;TZID=Europe/Dublin:20110630T103000
DTSTAMP:20110629T225234Z
SEQUENCE:8
END:VEVENT
END:VCALENDAR
After:
BEGIN:VEVENT
CREATED:20110629T224702Z
UID:04BBAED9-F08C-46C6-BB06-6D1ECE382C40
DTEND;TZID=Europe/Dublin:20110630T113000
RRULE:FREQ=DAILY;INTERVAL=1;COUNT=10
EXDATE;TZID=Europe/Dublin:20110701T103000,20110703T103000
TRANSP:OPAQUE
SUMMARY:Test
DTSTART;TZID=Europe/Dublin:20110630T103000
DTSTAMP:20110629T225234Z
SEQUENCE:8
END:VEVENT
END:VCALENDAR
The EXDATE line was added by copying, pasting and modifying the DTEND line; it causes the 1st and 3rd of July to be omitted from the recurrence. But note that there will now only be 8 occurrences, rather than the 10 initially specified.
Alternatively, you could write an Applescript to generate the recurring events; that is probably an even bigger pain.