shell脚本实现日历的屏幕控制

ch=1
while [ $ch != "0" ]
do
echo "******************************"
echo " 0.Exit      "
echo " 1.Display Calendar of month "
echo " 2.Display Calendar of year "
echo "******************************"
echo "Please choose number 1,2,or,0:"
read ch
if [ $ch = "1" ]
then echo "imput year:"
  read year
  echo "input month:"
  read month
  cal $month $year
else if [ $ch = "2" ]
  then echo "input year:"
   read year
   cal $year
  else if [ $ch = "0" ]
   then echo "Exit now!"
   else echo "Wrong choose!"
    echo "Please choose again!"
   fi
  fi
fi
echo " "
done