Shell Programming and Scripting

Yesterday=$(perl -e '@y=localtime(time()-86400);printf "%04d%02d%02d",$y[5]+1900,$y[4]+1,$y[3];')

date '+%m %d %Y' | 
{ 
read MONTH DAY YEAR
MINUS=10
TAIL_NO=`expr "$MINUS" - "4"` 
DAY=`expr "$DAY" - "$MINUS"`

#echo "DAY: "$DAY
#echo "TAIL: "$TAIL_NO

if [ "$DAY" -lt 1 ]
then 
       MONTH=`expr "$MONTH" - 1` 
                case "$MONTH" in 
                        0) 
                           MONTH=12 
                           YEAR=`expr "$YEAR" - 1` 
                        ;; 
                esac 
        DAY=`cal $MONTH $YEAR | grep . | fmt -1 | tail -$TAIL_NO | head -1` 
fi 

if [ $MONTH -lt 10 ]
then
	MONTH="0"${MONTH}
fi
if [ $DAY -lt 10 ]
then
	DAY="0"${DAY}
fi
date
echo "${MINUS} day(s) ago was: ${YEAR}${MONTH}${DAY}" 
}

date -v -1d "+%Y%m%d"

echo "2008/01/01" | awk -F"/" '{print $1$2($3-1)}'