判断用户输入的是否为目录

#!/bin/bash
while :
do
echo "please input your dectory"
read filename
while :
do
if [ -d $filename ];then
        echo "$filename is dectory";exit
else
        echo "$filename is not found"
        echo "please input exist D or mkdir"
        read D
        case $D in
        A)read filename;;
        B)break;;
        *)echo "error";;
        esac
fi
done
while :
do
        F=$filename
        echo "menu list"
        echo "y:mkdir directory"
        echo "n:not mkdir directory"
        echo "*：input other .exit"
        echo "please input choice y/n"
        read X
        case $X in
        Y) mkdir $F;exit;;
        N) echo "bu chuang jian ";exit;;
        Q) break;;
        esac
done
done