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Contrling crontab in script

Posted on 2006-10-30
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Last Modified: 2010-04-20

Hello,

In a script, user is allowed to set a schedule to make a backup but I need to limit it to one entry in crontab no more. What should I do?

should I count the number of lines in crontab and warn user or do you have a better idea?

Thanks,
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Question by:akohan
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8 Comments
 
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Accepted Solution

by:
Alticon-Brian earned 200 total points
ID: 17838207
What scripting language?

If you're keeping it to a straight bourne compatible shell you could do something like this:


proc_count=`grep scriptname /etc/crontab | wc -l`

Proc count will then have the number of times that the script is in there.  You can check and see if it's greater than zero, if it's not show a warning and run an exit(1) or something similar.

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Author Comment

by:akohan
ID: 17838334

Yes. I'm using regular bash.
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LVL 58

Assisted Solution

by:amit_g
amit_g earned 200 total points
ID: 17838499
if [ $(crontab -l | grep -v '^#' | wc -l) -le 1 ]
then
    echo "Less than or equal to 1 entry"
else
    echo "More than 1 entry"
fi
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LVL 23

Assisted Solution

by:Mysidia
Mysidia earned 200 total points
ID: 17838614
I would take the strategy of marking the line to crontab added by the script, and remove that line,
before adding a line.

I.E. when your script adds the crontab line, also add a trailing comment

[blah blah]  #Line Automatically Added: Leave this note intact


crontab -l |egrep -v '#Line Automatically Added: Leave this note intact$'  | crontab -

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LVL 48

Assisted Solution

by:Tintin
Tintin earned 200 total points
ID: 17838768
To borrow from amit_g's solution, but removing the need for wc

if [ $(crontab -l | grep -cv '^#') -le 1 ]
then
    echo "Less than or equal to 1 entry"
else
    echo "More than 1 entry"
fi
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