yesterday in UNIX

date '+%m %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
echo "Yesterday was: $MONTH $DAY $YEAR"