computing go/no-go dates in script - Shell Programming and Scripting

thumper · #1 03-22-2006

I am working on a bash script to backup selected servers and am trying to come up with a simpler solution to this problem:

Each server to be backed up has a config file that is read by the script, in the config file are the following values:
LEVEL0=12 #this is the day of the month on which level zero backups are performed.
INTERVAL=3: #In this case every 3 days before or after the LEVEL0 date an interval backup will be performed.

The LEVEL0 and INTERVAL values will be different for different servers.

I could just write a loop to compute if the current day is a day on which to perform an interval backup but it seems that there must be a simpler way to calculate this.

If anyone can point me in the right direction I would appreciate it very much.

blowtorch · #2 03-22-2006

If I am not wrong, you just have to determine if the date is one on which an interval backup is to be taken. You could use something like this:

Code:

#!/usr/bin/ksh
d=$(date +%d)

if [ $(($LEVEL0 - $INTERVAL)) -eq $d -o $(($LEVEL0 + $INTERVAL)) -eq $d ]; then
#### take backup here
fi

This bit will just check that it is a day on which you take the intermediate backup. For a level 0 backup, you can just check if the day of the month is the same as the LEVEL0 value.

thestevew · #3 03-23-2006

If you need an interval backup on every INTERVAL days before and after the full backup date then how about using a modulus from the full day number:

Code:

LEVEL0=12   ;# read these value from ...
INTERVAL=3 ;# ... parameter file

d=$(date +%d)

if [ $LEVEL0 -eq $d ]; then
    print backup is Full on day $d           ;# replace by doing something useful here ...
else
  if [ $(( ($d - $LEVEL0) % $INTERVAL)) -eq 0 ]; then
    print backup is Interval on day $d     ;# ... and here
  fi
fi

cheers

thumper · #4 03-23-2006

Quote:

Originally Posted by blowtorch

If I am not wrong, you just have to determine if the date is one on which an interval backup is to be taken. You could use something like this:

Code:

#!/usr/bin/ksh
d=$(date +%d)

if [ $(($LEVEL0 - $INTERVAL)) -eq $d -o $(($LEVEL0 + $INTERVAL)) -eq $d ]; then
#### take backup here
fi

This bit will just check that it is a day on which you take the intermediate backup. For a level 0 backup, you can just check if the day of the month is the same as the LEVEL0 value.

blowtorch Thanks. That solved the problem. I knew that there had to be a more elegant solution than what I was using. Tested the code against about 30 date/interval settings and it works as needed.

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