Shell Programming and Scripting

I don't agree with Scott - oddball date selections like this are hard to maintain - FWIW:
You should not try to do that with a crontab entry. You need to set up a calendar file that has the dates, for the whole year or two, of every saturday you want to run.

something like this goes in crontab

Code:

30 10 * * 6  /path/to/myscript.sh > /path/to/log.`date +%Y%m%d`

The first line of your script checks the "saturday" file you created:

Code:

  grep -q "`date +%Y%m%d`" /path/to/saturdayfile.dat  ||  exit 0

Awesome logic scott Really got amazed!!!

Thanks a ton for the solution.

-Mahi

Another way to detect the alternate Saturdays (assuming that month-boundaries are irrelevant). Look at the week number in the year and decide if it is an odd or an even number.

Code:

# Near top of script /path/to/myscript.sh (after Shebang line)
odd=$(($(date +%V)%2))    # Week number in year, divide by 2, take remainder 
if [ $odd -eq 1 ]
then
        exit
fi
if [ $odd -eq 0 ]
then
       echo "Even numbered week"
fi
# Rest of script

There are a ton of books on this subject - keeping code and business rules separated.
I work on a huge CIS which does not do that. I get a lot less sleep as a result.
So this kind of thing is a hot button for me. Dates are the very worst part of this deal, IMO.

While scott's approach is correct, a priori, the next guy may not know what the heck those gyrations are for. 90% of coding is done by the 'next guy'.

What happens when the OP finds out he has to skip the Saturday after some holiday?
Lots of holidays work on a lunar calendar, BTW. And many holidays are based on a separate non-Gregorian calendar, e.g. Hijri, Hebrew, etc. In Israel the Knesset decides when daylight savings time starts, and they sometimes do it a posteriori. Good Luck.

Just my point of view.

Unless there is a clear regular pattern, I usually set up a block of individual crons once a year. This covers abstract date patterns like Finance Month-End. It is also easy to adjust if there are exceptions such as hardware failure.
Jim's method is probably easier to maintain, but I prefer to have the whole schedule visible in crontab.