UNIX for Dummies Questions & Answers

Hello,

I would like to set-up a script in cron on a Solaris 10 sever which would run once in 3 weeks. I am not supposed to make any changes in the script itself.

Can anyone advise how it can be done?
For any queries, kindly let me know.


Thanks.

I don't have access to a Solaris machine and have no idea how cron on Solaris works. Right now I'm working on RHEL GNU Bash.

Here's one way to do it. You need not make any changes to the original script. You can write a wrapper script and have a tmp file containing the date of first run (date in tmp file should be in yyyymmdd format). Place this wrapper script and tmp file in same directory.

Wrapper script: A condition checks if the difference between current date and the date in tmp file is 21. If yes, run original script and change date in file to current date.

Code:

$ cat /home/user/date.tmp
20120207

The below code is untested.

Code:

$ cat /home/user/wrapper_script.sh
#! /bin/bash

if [ $((`date +%Y%m%d` - `cat date.tmp`)) -eq 21 ]
then
    date +%Y%m%d > date.tmp
    sh original_script.sh # Run original script.
fi

Now for the cron entry (Invoke wrapper script every monday at 9am):

Code:

0 9 * * 1    sh /home/user/wrapper_script.sh

Thanks for the above suggestion.
But .. since this is a restricted environment (client setup) I am not allowed to place my scripts on it, so I have to do it with cron.
If you would have done it on GNU, how would you do it with cron and not with script?
A few suggestions (to test out) would be appreciated!.
Thanks.

One way without a wrapper script and temporary file could be checking if the number of weeks since 1970-01-01 is divisible by 3. The crontab entry for every 3rd monday at 9 am:

Code:

0 9 * * 1  [ $((`date +%s` / 60 / 60 / 24 / 7 % 3)) -eq 0 ] && /path/to/your/script

From the sort of answers you are getting this is ambiguous.

Do you want to run this existing script once only on a specific date and time in three weeks time?
If that is true, I would use an "at" job (which uses cron). See "man at".

OR:

Do you want you run this existing script every third week at a specified time for evermore?

This crontab line will not work in Solaris because the default Shell for cron is the old Bourne Shell which does not support $(( )) syntax.
Also it contains a percentage sign "%" which is a special character in crontab files on all platforms.

Hmm, the calculation could be done using bc, but the problem with the percentage sign still remains, which makes an approach using the date command futile...