I am using this function to calculate yesterday's date and return it in the following format: Jan 09

date '+%b %d %Y' |
{
read MONTH DAY YEAR
DAY=`expr "$DAY" - 1`
case "$DAY" in
0)
MONTH=`expr "$MONTH" - 1`
case "$MONTH" in
0)
MONTH=12
YEAR=`expr "$YEAR" - 1`
;;
esac
DAY=`cal $MONTH $YEAR | grep . | fmt -1 | tail -1`
esac
((DAY < 10)) && DAY="0"$DAY
}

On the last day of December, it returned 31 and I wanted it to return Dec 31. Can someone tell me what could be wrong? After I return the value, I then am using it to grep a logfile, looking for yesterday's date.

That code is garbage. There must be some typos, but even allowing for that, "expr "Jan - 1"? You gotta be kidding. Navigate: our home page -> Answers to Frequently Asked Questions -> Yesterdays Date/Date Arithmetic and look for my datecalc routine. Then:

typeset -Z2 d
set -A months XXX Jan Feb Mar Apr May (etc)
datecalc -a $(date '+%Y %m %d') - 1 | read y m d
echo "${months[m]} $d"

I've put your function in a directory called functions. In the calling program I have the following:

. /app/manuv711/dnetwork/sfi/functions/datecalc

typeset -Z2 d
set -A months XXX Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
datecalc -a $(date '+%Y %m %d') - 1 | read y m d
echo "${months[m]} $d"


When I execute it all I get it this:

datecalc -a year month day - year month day
datecalc -a year month day [-|+] n
datecalc -d year month day
datecalc -D year month day
datecalc -j year month day
datecalc -j n
datecalc -l year month
use "datecalc -help" use for more documentation


Am I doing something wrong?

Lose that first line. Don't use the . command like that. Use the 4 lines that I posted. They assume that datecalc is on your PATH. If that's not the case, modify the third line to be a full path to datecalc.

Just for information, if you're using GNU date, you can do some *very* cool stuff with the "-d" option like

$ # get yesterdays date and format the output
$ date -d "yesterday" +"%d %b %Y"
10 Jan 2005

$ # get the date in two mondays time
$ date -d "next 2 monday"
Mon Jan 17 00:00:00 GMTST 2005

$ # 3 weeks ago...
$ date -d "3 weeks ago"
Tue Dec 21 14:06:44 GMTST 2004

You get the idea.

Cheers
ZB