Date maths in ksh script

[Mthales]

I have a script and in this I want to be able to take a date and work on the dates of the seven days before this date.

If the date is today then I can use the date command like this:

x=7
while [ $x -ge 0 ]
do
        DAY="$( date --date="${x} days ago" +%D)"
        ## work with the date I've found
        x=$(($x-1))
done

but how can I best do it for any other date?
Thanks for any help
Emma

--------------------------------------
For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks.
-- Terry Pratchett, Equal Rites

 

[lpblauen]

This is how I get days gone by. Hope it helps.
# days 1 which is 1 x 24 + 5 = 29
a1=`env TZ=CST6CDT+29 date`
echo $a1

this is 24 hours ago
formula I use is
1 x 24 +5 =29 or 24 hours ago
2 x 24 +5 =53 or 48 hours ago
3 x 24 +5 =77 or 3 days ago etc ......

$env TZ=CST6CDT+29 date
Tue Oct 17 09:39:00 CDT 2006
$env TZ=CST6CDT+53 date
Mon Oct 16 09:39:07 CDT 2006
$env TZ=CST6CDT+77 date
Sun Oct 15 09:39:51 CDT 2006
$env TZ=CST6CDT+101 date
Sat Oct 14 09:40:13 CDT 2006

 

[Mthales]

Thanks for your answer lpblauen but I'm not quite sure I understand what you mean.

I've managed to coble together a messy way of doing what I want so maybe you can offer some advice on that:

## get today's date
TODAY=$( date +%D)
## get the seconds since epoc for today
TODAY=$( date --date=${TODAY} +%s)

## get the seconds since epoc for the date I want to work from
DIFF=$( date --date=${DAY} +%s)

## subtract the old date from today
DIFF=$((${TODAY}-${DIFF}))
## devide by the number of seconds in a day
DIFF=$((${DIFF}/86400))
## so I know how many days ago that date was 

## ... so THATDAY should match DAY
THATDAY=$( date --date="${DIFF} days ago" +%D)

## then for the whole of the week before that day
k=6
while [ $k -ge 0 ]
do
       THISDAY=$(date --date="$((${DIFF}+${k})) days ago" +%d%m%Y)
       ## work on THISDAY
done

Does that make my question any clearer?
Emma

--------------------------------------
For animals, the entire universe has been neatly divided into things to (a) mate with, (b) eat, (c) run away from, and (d) rocks.
-- Terry Pratchett, Equal Rites

 

[lpblauen]

You can't subtract a date form a date that I know. Here is a script to go back up to 10 days. Try it maybe you can use it to make your script.

#set -x
if [ $# -ne 1 ]; then
echo " Valid args are numbers 1 thur 10 for # of days."
exit 1
fi
# here we set the days. we want to go back up to 10.
# this is based on eastern time. day x 24 +5 = 24hr ago.
case "$1" in
1) x=29;;
2) x=53;;
3) x=77;;
4) x=101;;
5) x=125;;
6) x=149;;
7) x=173;;
8) x=193;;
9) x=221;;
10) x=245;;
*) echo " Valid args are numbers 1 thur 10 for days."; exit 1;;
esac
ee=`env TZ=+$x date +"%D"`
echo $ee

 

[Annihilannic]

She's not subtracting dates as such, but seconds from the epoch, which should be fine.

That script looks good to me Emma, if it works fine for you, use it!

Annihilannic.