What does "read -n1 -s" mean in this script?

Question

Today I have learned some tricks about menu option in command line. One of these was

cat << EOF
    Some lines
EOF
read -n1 -s
case $newvar in
   "1") echo "";
ecsa 

It's really magical. I can't find any description in man page about this option. How the input to read command was pushed into case option ? It usually use a variable to do this thing as I know.

I just want to understand the process of this combination further.

while :
do
    clear
    cat<<EOF
    ==============================
    Menu Install DHCP Tool
    ------------------------------
    Please enter your choice:

    (1) Config Network Interface
    (2) Check status
    (3) Config DHCP server
    (Q)uit
    ------------------------------
EOF
read -n1 -s
    case "$REPLY" in
    "1")  config_network ;;
    "2")  check_status ;;
    "3")  config_dhcp ;;
    "q")  exit                      ;;
     * )  echo "invalid option"     ;;
    esac
    sleep 0.2
done

Answer 1

The documentation of read notes that:

If no names are supplied, the line read is assigned to the variable REPLY.

From that point it's a normal case statement. -n1 reads a single byte and -s turns off terminal echo of the input.

Answer 2

The variable $newvar you use in your short description doesn't exist.

It must be $REPLY, as you actually use in the full command.

This issues have no relation to the read options -n1 -s you are asking about.