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Full Discussion: Scheduling a command to run every 3 days through cron
Top Forums Shell Programming and Scripting Scheduling a command to run every 3 days through cron Post 302344992 by jim mcnamara on Tuesday 18th of August 2009 07:07:41 AM
Old 08-18-2009
The problem with using DOW is that there are 7 days - plus sunday may not be day 0 depending on your locale. 7 does not divide evenly by 3.

If you literally want every third day try setting up a daily cron entry that checks for "thirdness"
Code:
$(date +%s)/86400

is the number of days since Jan 1 1970. # of days % 3 == 0 means it is a day divisible evenly by three.
This trick works for any weird number of days that don't track well as a DOW or a fixed day in the month.


Code:
[[ $(( ($(date +%s)/86400) % 3   )) -eq 0 ]] && /home/me/myscript.sh

Last edited by jim mcnamara; 08-18-2009 at 08:21 AM..
 

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LEARN ABOUT MINIX

calendar

CALENDAR(1)						      General Commands Manual						       CALENDAR(1)

NAME

       calendar - reminder service

SYNOPSIS

       calendar [-] [-r]

OPTIONS

       -      Work for every user and send mail to him

       -r     Restrict multiple execution on the same day

EXAMPLES

       calendar 	   # Check calendar file in current directory

       calendar 	   # Normary used under the control of cron(8)

       calendar -r	   #  Normary used in /etc/rc file

DESCRIPTION

       Basically  calendar program consults the file calendar in the current directory and display lines which contain today's or tomorrow's date.
       Month-day formats such as '12/25', 'Dec. 25', 'december 25', '*/25', '12/*', '*/*' are recognized.  The asterisk means 'all' days or  'all'
       months.	 On  weekends  'tomorrow' extends through next Monday without any consideration about holidays.  To prevent ambiguity, the formats
       '25 Dec.' and '25/12' are not recognized.

       When an argument - is present, calendar works for all users with a file calendar in their login directories and sends them mail.   Normally
       this is done daily under the control of cron.

       The  -r	option	does  its the same job as - option, but touches the calendar to prevents further access on the same day.  Normally this is
       done in the /etc/rc file on a machine  which may be booted several times in one day.

SEE ALSO

       cron(8).

																       CALENDAR(1)
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