Basic Shell / Bash Programming Linux / Unix

echo "what month..." read month echo "what year..." read yearif test " $month = [1-12] "
then cal "$month" "$year"
echo "you are now being redirected to the menu"
bash program.sh else echo " you entered a wrong number for month" exit 0
fi



So Im trying to write a command that shows a specific month and year you typed for the selections you enter but I can't figured to prevent the error cal month 13 is not a month...

Here's what is supposed to do....You typed a number for a month you are looking for, example january 1,february 2you typed a number for the year you are looking for ,example year 2012,2013 but I want to prevent that if the user types for instance month 13which is non existance to return him to the main menu which will run the script again..