shell script : if condition

[will@localhost ShellScript]$ cat cond.if.sh

#!/bin/sh

read -p "Please input (Y/N): " yn

if [ "$yn" == "Y" ] || [ "$yn" == "y" ]; then

echo "Oh, Yes!"

elif [ "$yn" == "N" ] || [ "$yn" == "n" ]; then

echo "Oh, No!"

else

echo "I don't know what your choice is."
fi