[Gllug] Crontab schedule question

[Benedikt Heinen]

>>> 0 12 * * 1/2

>>> do the job?

>> That'll run it at 12pm every Monday, Wednesday and Friday.
> Wouldn't that be

> 0 12 * * */2

> I am just guessing here.

Nope - that's also calling the script every other day of the week (5th 
column is day of week). If the weekday isn't important you should be able 
to try for

 	0 12 */14 * *

Or - but even that wouldn't go strictly every other week (it could during 
month changes skip another week, might be  (hope I'll have this correct):

 	0  12  1-7,15-21 *  1

which should run your script on every Monday that is on a 1st-7th of a 
month, and every Monday that is a 15th-22nd of a month. But - there will 
be months with two Mondays in the period between 22nd-31st of the month. 
So if you can live with the occasional skip, the above should work.

If you can't live with a skip of a week, but could live with occasionally 
running two consecutive weeks, you could adapt it into

 	0  12  1-7,15-21,29-31 *  1

just to make it run the extra time at the end of the month.

Apart from that, you'd need to run your job from within a wrapper script 
that touches a flag file, whenever it runs the wrapped script, but will 
always first check whether the flag file is older than say 13 days... Such 
a script could then be run every monday, but it would still only actually 
do the work you want every other week...

another approach, also using a wrapper script would be to check whether 
it's an odd or even week (e.g. for sh:

 	wk=`date +%W`
 	if [ `expr $wk % 2 ` == 1 ]; then
 	  # odd week number
 	  ./doYourStuff -whateverflags and parameters necessary
 	fi

This, though, would once a year re-introduce the problem mentioned earlier 
(depending on whether there is a Monday - or whatever weekday is chosen - 
in the last couple of days in the year or not)



Benedikt

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