cron bash date

[Lance Hoffmeyer]

Hello,

I am trying to run a bash script in cron. I originally wanted
it to run at 11:59pm on the last day of every month. February
will always cause problems because of leap years. Therefore,
I decided to run cron on the first day of every month using
the @month parameter.

The problem is that I want the month to reflect the previous month.

MON=$((`date +%m`-1))

This will work for every month except January where instead of getting 12
I get 0. 2 questions

1) How can I modify the above line so that if `date *%m`-1 = 0 then MON=12
2) I want the output to be 01-09 and not 1-9. How can I change the format
to add a zero? +%m usually adds a zero but subtracting 1 causes the 0
to be removed.

Lance






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[David Z Maze]

Lance Hoffmeyer <lance@augustmail.com> writes:

> I am trying to run a bash script in cron. I originally wanted
> it to run at 11:59pm on the last day of every month. February
> will always cause problems because of leap years. Therefore,
> I decided to run cron on the first day of every month using
> the @month parameter.

crontab(5) doesn't suggest a good way to do this, no. So yeah,
running early (say, 12:03 AM) on the first of the month is easy:

3 0 1 * * /usr/local/sbin/ourscript

> The problem is that I want the month to reflect the previous month.
>
> MON=$((`date +%m`-1))

How about:

MON=`date -d yesterday +%m`

date(1) seems to think "yesterday" is exactly 24 hours ago, if you're
looking at other fields. (Or maybe it's exactly a day ago; this makes
a difference around daylight savings.)

--
David Maze [email]dmaze@debian.org[/email] [url]http://people.debian.org/~dmaze/[/url]
"Theoretical politics is interesting. Politicking should be illegal."
-- Abra Mitchell


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[Vineet Kumar]

* David Z Maze (dmaze@debian.org) [030801 07:13]:

> Lance Hoffmeyer <lance@augustmail.com> writes:
>

> > I am trying to run a bash script in cron. I originally wanted
> > it to run at 11:59pm on the last day of every month. February
> > will always cause problems because of leap years. Therefore,
> > I decided to run cron on the first day of every month using
> > the @month parameter.

>
> crontab(5) doesn't suggest a good way to do this, no. So yeah,
> running early (say, 12:03 AM) on the first of the month is easy:
>
> 3 0 1 * * /usr/local/sbin/ourscript
>

> > The problem is that I want the month to reflect the previous month.
> >
> > MON=$((`date +%m`-1))

>
> How about:
>
> MON=`date -d yesterday +%m`

Oh yeah, I forgot about that, duh! =p That's way cleaner than my daily
touching a file idea.

> date(1) seems to think "yesterday" is exactly 24 hours ago, if you're
> looking at other fields. (Or maybe it's exactly a day ago; this makes
> a difference around daylight savings.)

date actually understands a pretty wide array of expressions. So if
"yesterday" isn't to your liking, you can also use $(date -d "24 hours
ago"). Also, I think the OP will then easily see how to have a script
running early on the first of the month can give the date of 23:59
yesterday, by, say, running at 00:05 and asking date for "6 minutes
ago".

good times,
Vineet
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A: No.
Q: Should I include quotations after my reply?

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