[ale] cron entry that runs the 2nd saturday of every month

Fri Aug 26 18:45:52 EDT 2011

On Fri, 2011-08-26 at 16:47 -0400, Erik Mathis wrote: 
> I ran into this same issue, and iirc cron uses a AND to compare dates.
> I ended up running it every Monday and added a wrapper to the script
> to decide if its the right day to do this function. If not, just exit.

No, there's a gotcha in there.  It uses "AND" to compare time and then
only one of two particular fields (day of month or day of week) have to
be true, so that's an OR.  That's a PITA.

From "man 5 crontab":

== 
Note: The day of a command's execution can be specified in the  follow‐
ing two fields — 'day of month', and 'day of week'.  If both fields are
restricted (i.e., do not contain the "*" character), the  command  will
be run when either field matches the current time.  For example,
"30  4  1,15 * 5" would cause a command to be run at 4:30 am on the 1st
and 15th of each month, plus every Friday.
== 

The exact opposite of what you want.

I actually have a more complex example that would work if it truly WAS
an AND (and I can think of no useful reason for it being an OR but it
is).

Real world situation.  I have a meeting to take place to take on the
Wednesday following the 2nd Tuesday.  Notice that it is NOT the the
second Wednesday.  One Wednesday out of every 7 will be the third
Wednesday.  So I would need a Wednesday that's on 9-15 (15 being the 3rd
Wednesday with 1 and 8 being the first two).  An AND condition would be
perfect.  Tis not to be.  Thou must script.

> -Erik-

Regards.
Mike

> On Fri, Aug 26, 2011 at 4:27 PM, Geoffrey Myers
> <lists at serioustechnology.com> wrote:
> > Lightner, Jeff wrote:
> >> But the OP wanted 2nd Saturday only.  The +%u just tells you it is
> >> Saturday - not which Saturday.
> >
> > I am the op.  Using the combination of the day of the week and the day
> > of the month you can calculate whether its the 2nd Saturday of the month
> > or not.
> >
> >>
> >> I had tested for it being Saturday in my 2008 script but if the cron
> >> job only runs on Saturday it isn't really necessary.   (My test was
> >> to prevent someone from just moving the cron job without
> >> understanding its purpose.)
> >>
> >> -----Original Message----- From: ale-bounces at ale.org
> >> [mailto:ale-bounces at ale.org] On Behalf Of Geoffrey Myers Sent:
> >> Friday, August 26, 2011 3:39 PM To: Atlanta Linux Enthusiasts
> >> Subject: Re: [ale] cron entry that runs the 2nd saturday of every
> >> month
> >>
> >> Lightner, Jeff wrote:
> >>> When I had to do this back in 2008 on HP-UX I worked out a script
> >>> that relied on the cal (calendar) command.
> >>>
> >>> The following command line will give you the 2nd Saturday of the
> >>> month:
> >>>
> >>> cal |cut -c19-20 |grep '[0-9]'|head -2 |tail -1
> >>>
> >>> The following command will give you today's day of month: date +%d
> >>
> >> Doing something similar only relying on date alone:
> >>
> >> date +%d date +%u
> >>
> >>> You put your script to compare day of month with the output of the
> >>> cal line and run the desired command if they match.   Then your
> >>> cron entry runs EVERY Saturday and the script determines whether to
> >>> run the commands you want based on whether it is the 2nd Saturday.
> >>>
> >>> There may be easier ways to do this on Linux but I figured I'd send
> >>>  you this at least as a basis for thought.
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> -----Original Message----- From: ale-bounces at ale.org
> >>> [mailto:ale-bounces at ale.org] On Behalf Of Geoffrey Myers Sent:
> >>> Friday, August 26, 2011 2:26 PM To: Atlanta Linux Enthusiasts
> >>> Subject: [ale] cron entry that runs the 2nd saturday of every month
> >>>
> >>>
> >>> Is it possible?
> >>>
> >>> -- Until later, Geoffrey
> >>>
> >>> "I predict future happiness for America if they can prevent the
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> >>>
> >>>
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> >>>
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> >
> >
> > --
> > Until later, Geoffrey
> >
> > "I predict future happiness for America if they can prevent
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-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
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