利用Shell脚本获取前天日期

YEAR=`date +%Y`
DAY=`date +%d`
MONTH=`date +%m`

DAY=`expr $DAY - 2`
if [ $DAY -le 0 ]; then
  MONTH=`expr $MONTH - 1`
  if [ $MONTH -eq 0 ]; then
   MONTH=12
   YEAR=`expr $YEAR - 1`
  fi
  LASTLINE=`cal $MONTH $YEAR | grep "[0-9]" | tail -1`
  LASTDAY=`echo $LASTLINE | sed "s/.* \([0-9][0-9]*\)/\1/"`
  if [ $DAY -lt 0 ]; then
   DAY=`expr $LASTDAY - 1`
  else
   DAY=$LASTDAY
  fi
fi
if [ $MONTH -lt 10 ]; then
  MONTH=0$MONTH
fi
if [ $DAY -lt 10 ]; then
  DAY=0$DAY
fi
qiantian="$YEAR$MONTH$DAY"
echo $qiantian