Cron Question

[f. halili]

How do we format this this in the crontab file?

Run "/scripts/backup" every last friday of the month at 6:00am ??

Thanks,
f.halili

[Steven E. Protter]

The tricky part is the last friday of the month.

What you should do is run a script every friday and use caljs.sh, an A. Clay Stepenson invention to determine if it is ineed the last friday of the month and go forward with the backup.

Shell version:
http://www.hpux.ws/merijn/caljd-2.23.sh

Perl version
http://www.hpux.ws/merijn/caljd-2.2.pl

crontab entry:

* * * * 5 /command

SEP

[James A. Donovan]

Well....there are only twelve last Friday's of the month each year.

Put each one on a different line (12 lines in all)

[A. Clay Stephenson]

Using the aforementioned caljd.sh script this is easy. You run you cronjob every Friday and the script itself determines if this is the last Friday by seeing if today and 7 days from now are in a different month. Your should set and export PATH in your script to include the location of caljd.sh or use full pathnames:

#!/usr/bin/sh

export PATH=${PATH}:/usr/local/bin

if [[ $(caljd.sh -M) != $(caljd.sh -n 7 -M) ]]
then
echo "Do your thing; it's the last Friday"
fi

[Nguyen Anh Tien]

This is only this you need
#crontab -e
# Minute Hour MonthDay Month Weekday Command
# ----------------------------------------------------------
0 06 * * 5 /sbin/sh your_path/script


Notes: 0=Sunday, 1=Mon ...5 =Friday
tienna

[Ivajlo Yanakiev]

Nguyen Anh Tien is realy right :)

[Pete Randall]

How do you figure that's right? It looks to me like that would run every Friday.


Pete

[Doug Kratky]

If you could live with the 4th Friday every month instead of the last Friday, you could do:
0 06 21-28 * 5 /scripts_dir/backup

[A. Clay Stephenson]

This suggested solution
0 06 21-28 * 5 /scripts_dir/backup
will certainly run on the last Friday of the month but sadly it will also run on every other Friday of the month as well. In addition, it will also execute the command every doy of the month from the 21st to the 28th. When weekdays and monthdays are specified in cron, the result is not a logical AND but is rather a logical OR.

Use the solution I suggested earlier.

[Prashant Zanwar_4]

You can do some tricky calculation, like just take last date of month as 30 & 31, you can do it monthwise...
DO a minus on this day and see what is the day..using some date format, if the day turns out to be friday, you can execute the command..

date would be 31,30,28

do 31 - 5,4,3,2,1,0...see what it returns..execute ur script if it is friday...
you can divide the script in 3parts probably..and call from a small script in cron..

Hope it helps
Thanks and regards
Prashant

[Sergejs Svitnevs]

My solution:

Crontab (starts custom script every friday) :
0 6 * * 5 /scripts/backup_start

Script (checks condition: if today is last friday then execute main script):

#!/usr/bin/ksh
Last_day_in_month=`cal | sed '/^$/d' | tail -1 | head -1 | awk '{print $NF}'`
Today=`date +%d`
if [ `expr $Today + 7` \=> `expr $Last_day_in_month` ]
then

fi

Regards,
Sergejs

[Marlou Everson]

Another variation would require adding a few lines to the backup script and 3 cron entries.

# Check if day is Fri
today=$(date +%a)
if [ "$today" != "Fri" ]
then
echo "Okay, will not run now since today is $today and not Fri."
exit
fi


00 06 25-31 1,3,5,7,8,10,12 * /scripts/backup
00 06 24-30 4,6,9,11 * /scripts/backup
00 06 22-28 2 * /scripts/backup

This would still require a method to deal with February when it has 29 days with the 29th on a Friday.

Switching to the first Friday of the month let's you just run the script on days 1 through 7.

Marlou

[Anthony Villanueva]

Hi,

I think Clay's solution is the simplest and you can be sure that it will run on the last Friday of the month. Why complicate it, right?

[f. halili]

thanks for all the inputs.