How to set crontab for run in the last date of month?: Linux, Scripting, Bash, Crontab

by: nociPosted on 2009-08-06 at 03:29:33ID: 25031729

there are two aproaches:
1) use cron (is problematic in case of 29th of february), you might update the crontab every year at beginning of the year.

0 0 31 1,3,5,7,8,10,12 * runscript
0 0 30 4,6,9,11 * runscript
0 0 28 2 * runscript
0 0 15 * * runscript

2) run a script and have the script check if the next DAY is 1....
0 0 15,28-31 * * runscript

in runscript use the date command with various formats the check the current date (15) to run
and the if the next date. You might need a small script to return the the date of current time +86400 seconds.

by: RBEIMSPosted on 2009-08-06 at 04:11:17ID: 25031958

You can use this script. It generates the crontab line that you can use to configure cron for the current month. It takes leap years into account thanks to the script found here:
http://bash.cyberciti.biz/time-and-date/find-whether-year-ls-leap-or-not/

I just got the script and made the adjustments necessary to make your desired function.

#!/bin/bash
# Shell program to read any year and find whether leap year or not
# -----------------------------------------------
# Copyright (c) 2005 nixCraft project <http://cyberciti.biz/fb/>
# This script is licensed under GNU GPL version 2.0 or above
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# -------------------------------------------------------------------------
 
# store year
yy_date=`date +%y`
yy="10#$yy_date"
isleap="false"
declare -a months_table 
    months_table[1]="31";
   months_table[2]="28";
   months_table[3]="31";
   months_table[4]="30";
   months_table[5]="31";
   months_table[6]="30";
   months_table[7]="31";
   months_table[8]="31";
   months_table[9]="30";
   months_table[10]="31";
   months_table[11]="30";
   months_table[12]="31";
 
# find out if it is a leap year or not
 
if [ $((yy % 4)) -ne 0 ] ; then
   : #  not a leap year : means do nothing and use old value of isleap
elif [ $((yy % 400)) -eq 0 ] ; then
   # yes, it's a leap year
   isleap="true"
elif [ $((yy % 100)) -eq 0 ] ; then
   : # not a leap year do nothing and use old value of isleap
else
   # it is a leap year
   isleap="true"
fi
if [ "$isleap" == "true" ];
then 
   ${months_table[2]} = "29";
fi
current_month_date=`date +%m`
current_month="10#$current_month_date"
last_day=${months_table[$current_month]}
command="some/command"
echo "59 59 $last_day * * $command"

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by: it4sohoPosted on 2009-08-06 at 09:53:13ID: 25035556

As is apparent from the above posts, the CRON daemon doesn't have an easy way to specify the last day of a month (similarly, it cannot easily do "the 2nd tuesday" of the month... although that one IS possible).

Instead, I recommend that you run your script on the 28th-31st of all months, and determine within your script if this date is truly the last day of the month.

My next question is more basic... given the capabilities of cron, is that one minute on the 15th & last day all that important? (NOTE: unless you put a delay in, cron cannot run your script at 23:59:59 -- only "very soon after 23:59:00". This is because cron's timing is valid only to the nearest minute, not second.)

So what if you ran your scripts one minute later -- at midnight (0:00) on the 1st and 16th?

Sure would make things easier!

That being said, while the algorithm above for computing whether it is a leap-year is 100% valid, you should note that simply testing for divisible by 4 will work for another 90 years (the next century where a leap-year is skipped is 2/28/2100), and the next century where a leap year will NOT be skipped is 390 years away - 2/29/2400)... we're not likely to be around for either, and neither are the systems we're working on today!

[If you don't know the convoluted rules for leap year, look here: http://en.wikipedia.org/wiki/Leap_year for FAR more information than you could possibly WANT to know about leap years.]

One last item... the LAST line in the script above means it will NEVER run... the format for crontabs is
MIN HOUR DAY MONTH WDAY [USER] command
Since there is no 59th hour, it will never run...
the correct last line would therefore be:
59 23 $last_day * * $command

But again, for the sake of a single minute, you REALLY might want to consider:
0 0 1,16 * * command
and run your command in the FIRST minute of the NEW 1/2-month, instead of trying to fit it into the LAST minute of the OLD 1/2-month.

But that's just me....

Good luck!

Dan
IT4SOHO

by: RBEIMSPosted on 2009-08-06 at 10:00:44ID: 25035619

Yeah, the last line in the script was really wrong. Thanks for pointing that out!
And I agree that it would be much simpler to just do it on the first of each month...

by: nociPosted on 2009-08-06 at 11:49:35ID: 25036752

to check if tomorrow is the first you can use:

This is not that complex to compute....

runscript:
---8<---
#/bin/bash
tomorrow=$( perl -e '@x=localtime( time()+86400 ); print $x[3] ."\n" ' )

if [ "$tomorrow" == 1 -o "$tomorrow" == 16 ] ; then

#lets do somthing usefull here...

fi
exit
---8<---

by: NopiusPosted on 2009-08-09 at 20:24:31ID: 25057008

> I want to run a script or program under crontab scheduler. My schedule is in each 15th (23:59:59) and last date of the month, which last date of the month means 28th, 29th, 30th or 31th, (all at 23:59:59) depend on the month.

> How to detect date of last month, so my script/program can be scheduled at last date of the month?

Just run it at 00:00 1st day of the next month. It is almost the same as 23:59 of the day before :-)

by: gheistPosted on 2009-08-10 at 14:52:09ID: 25064422

On linux I think you can do date -d tomorrow
For others "cal" && action
may help

by: a_didit_mPosted on 2009-08-10 at 15:04:10ID: 25064519

Dear All,

I prefer to use RBEIMS scripts in 2nd posting in this thread, but I'm consulting to my web hosting, because they deny my bash script to be executed.

Anyway, run script or cron schedule in 1st day is already become my consideration before I posted this topic. For now I prefer to run at last day because my other scripts have date criterias in range.

by: it4sohoPosted on 2009-08-11 at 09:56:27ID: 25071036

Your BASH script must be executable to run from a cron job...
chmod u+x /path/to/script

Dan
IT4SOHO

PS: Your experience is an example of the double-edged sword that is *nix... there are 1000 ways to do virtually anything! Leaving YOU, the SA, to decide which is best for you!

by: a_didit_mPosted on 2009-08-11 at 22:56:39ID: 25076021

Thanks All ...

My host Administrator will allow to execute the script under his privilege, not under general privileges.

by: a_didit_mPosted on 2009-08-11 at 23:11:19ID: 31612304

Thanks All ..

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How to set crontab for run in the last date of month?

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