[SOLVED] Scheduling a CRON job to run on the first Sunday of the month

New2Linux2 · 02-01-2007, 12:18 PM

Does anybody know how to tell cron to run a job on the first Sunday of the month? I can tell it to run every 4th sunday, but that doesn't quite work for backups. Any ideas?

colucix · 02-01-2007, 12:31 PM

In my opinion it is not possible using the time and date fields of the crontab entry. But you can always check for date at the very beginning of your script and execute the rest only if day of the month is less than 7. For example:

Code:

05 4 * * 0 /some/dir/my_scrip.sh

execute my_script.sh every Sunday, and at the beginning of the script:

Code:

#!/bin/bash
if [ `date +%d` -gt 7 ] ; then
   exit
else
   <my commands>
fi

New2Linux2 · 02-01-2007, 12:51 PM

PERFECT!!!!
That does exactly what I need. Thank you very much.

New2Linux2 · 02-12-2007, 03:02 PM

Ok, it didn't work right. This last Sunday (Feb 11th) the backup that was only supposed to run on the first Sunday of the month, ran. Here is the script (/etc/.full-system-backup.sh) that I used:

Code:

#!/bin/bash
if [ 'date +%d' -gt 7 ] ; then
        exit
else
        tob -rc /etc/tob/disk.rc -full system
fi

In /etc/crontab is this entry:

Code:

10 0 * * 0 root /etc/.full-system-backup.sh

The way I read it, it is supposed to work like this:

Every Sunday at 12:10AM crontab runs the script /etc/.full-system-backup.sh
That script runs a check to see if the day of the month is greater than 7
- If the DOM is greater than 7, the script exits doing nothing
- If the DOM is not greater than 7, the script runs the command "tob -rc /etc/tob/disk.rc -full system" and exits when that is complete

The command "tob -rc /etc/tob/disk.rc -full system" works for running a backup of my system configuration when run from the command prompt. The backup completed without errors, just on the wrong day.

I have limited experience with scripts so I'm not sure what went wrong with the above script. To my mind, the same thing would happen if this were used:

Code:

#!/bin/bash
if [ 'date +%d' -lt 8 ] ; then
        tob -rc /etc/tob/disk.rc -full system
else
        exit
fi

Of course, I don't want the same thing to happen, I want it to actually work right.

Any Ideas?

colucix · 02-12-2007, 03:18 PM

Uh oh... it can pass unnoticed, but looking at the script I posted above and the one you have just posted, the only and unique difference does the trick:

Code:

if [ 'date +%d' -gt 7 ] ; then     # this is wrong
if [ `date +%d` -gt 7 ] ; then     # this is correct

the former has single quotes enclosing the date command, the latter has reversed single quotes. The reversed single quote is a bash syntax which gives the result of the command enclosed. Normal single quotes, instead, give the string as is. You can verify the different behaviour issuing the following commands

Code:

echo 'date +%d'
echo `date +%d`

Hence in your script the condition is always false! Furthermore, I wonder why it did not give an error, since the -lt operator is for arithmetic comparison only and should not accept strings as arguments. By the way, the reversed quotes are the answer to the question!

New2Linux2 · 02-12-2007, 03:56 PM

D'OH
Thanks.

balius · 05-27-2011, 07:00 AM

#Should run every first Sunday of each month at 9AM (first Sunday is only when day number is between 1 and 7)
0 9 1-7 * 0 /script.sh

kakapo · 11-25-2011, 07:36 AM

No baluis "0 9 1-7 * 0 /script.sh" will run script.sh every sunday at 9 a.m. and on each the first seven days of the month as well. The day of month and day of week fields are OR'd not AND'd.

I prefer this form because you can see what you are running.

0 9 1-7 * * [ "$(date '+\%a')" == "Sun" ] && <path>/script.sh

archangel_617b · 04-11-2013, 11:10 AM

Quote:

Originally Posted by kakapo

I prefer this form because you can see what you are running.

0 9 1-7 * * [ "$(date '+\%a')" == "Sun" ] && <path>/script.sh

Wow! I've been using the "m h * * Sun [ date +%d -le 7 ] && ..." form for years but this is *far* clearer and more flexible. Thanks

jbmart · 08-05-2013, 11:42 AM

Quote:

I prefer this form because you can see what you are running.

0 9 1-7 * * [ "$(date '+\%a')" == "Sun" ] && <path>/script.sh

This worked for me, with one exception. Everytime cron ran this, it would fail with

Code:

[: 1: Thu: unexpected operator

("Thu" being which ever day of the week it ran).

I removed one = sign, changing the code to

Code:

0 9 1-7 * * [ "$(date '+\%a')" = "Sun" ] && <path>/script.sh

Now it works. This was on a machine running Debian 7.

FWIW.

kzo81 · 11-08-2016, 12:25 PM

Quote:

Originally Posted by colucix

Uh oh... it can pass unnoticed, but looking at the script I posted above and the one you have just posted, the only and unique difference does the trick:

Code:

if [ 'date +%d' -gt 7 ] ; then     # this is wrong
if [ `date +%d` -gt 7 ] ; then     # this is correct

)

this one is also OK:

if [ $(date +%d) -gt 7 ]; then ...