Shell Programming and Scripting

Thanks! Although a monthly backup may take place on say the 1st. It's not necessarily the last Friday of the month. I'm not really sure how I can write this down clearly. There is an example in post 3 ^

If I understand your code that will run it the first, second and third Friday, but not the fourth of each month, whereas we require it to run on every fourth week.

I was thinking along the lines of using an initial date, then +28 days (multiple). Since there is no set date as such the monthly backups take place, its every four weeks. So we could start the cycle in the script on whatever date. For example, I know our next monthly backups begin on Friday 30th April 2010. Here is a few dates after this to try and give more of an idea of the cycle -

30th April (Just happens to be the last Friday)
28th May (Just happens to be the last Friday)
25th June (Just happens to be the last Friday)
23rd July (Not the last Friday, it's in fact the 4th out of 5 Fridays in July)
20th August (Not the last Friday either, it's the 3rd out of 4)

The reason it is set a little odd like this is because it's the weekend after our pay (we get paid 4 weekly, not monthly).

Hope this makes sense.

Thanks for the replies!
Rab



Edit - Poor attempt at pseudo like code below

Cron Entry - 00 21 * * 5 /backupscript

backupscript -

Code:

if todays date is +28 (multiple) 30th April 
then run monthly backup
else run normal backup
fi

There is probably a better way to do it, I don't know enough about scripting to get my head around it



Edit 2 - This is AIX v5.3 if it makes any difference.

Any solution will need to know when the last monthly backup ran or when the next monthly backup is scheduled to run, perhaps by having that info stored in a file by the monthly backup process. With that info in hand, it should be easy enough for the daily to decide if it should run on any given friday.

Regards,
Alister

Good point.

Perhaps adding into the monthly backup script a touch command to create a file with todays date +28 days.

Then on the call script in the cron check to see if that date matches todays date? Would this work?

I'm not so sure on the syntax for this though, or if it is possible (I imagine it is though).

Thanks!
Rab

You want to to run a weekly backup script every week except every fourth week of the year when you want to run a different script/command.
What about

Code:

if [ $(date +%u) -eq 5 -a $((($(date +%j) / 7) % 4)) -gt 0 ];then echo fourth week ;else echo regular week;fi

Edit:
Let's explain :If you run my code tomorrow (April 23, 2010) will be a fourth week Friday

I'll give it a try with some overly commented code.
Oh. And run it as a cron job every friday.

Code:

#!/bin/bash

# name of file to keep track of last backup
lastbackup=./lastbackup

if [ -f $lastbackup ]
then

# Time of last backup (seconds since epoch)
    timelast=$(stat -c %Y $lastbackup)

# Current time (seconds since epoch)
    timenow=$(date +%s)

# 86400 sec per day. 28 days is four weeks
    fourweeks=$(( 86400 * 28 ))

# slacktime = Some slack so we survive bad clock
# and daylight saving time. (2h)
    slacktime=$(( 3600 * 2 ))

# Have more than four weeks passed? (minus 2h)
    timepassed=$(( $timenow - $timelast ))
    fourweeksslack=$(( $fourweeks - $slacktime))

    if [ $timepassed -gt $fourweeksslack ]
    then
        echo BackupBackupBackup
    else
        echo NoBackup
    fi
else
# Should only occur first time script is run
    echo $lastbackup was created
    touch $lastbackup
fi

The logic of the test command does not agree with the echo statements. It will echo "fourth week" 3 out of 4 fridays.

Instead of "-gt 0", "-eq 3" should harmonize with the echo statements.

Regards,
Alister

You can use the +%U format which gives the week number (as i posted above).

Code:

(( $(date +%U) % 4))

will return false 1/4 and true 3/4