shell实现自动挂载优盘

#!/bin/sh
is_empty_dir(){
    return `ls -A $1|wc -w`
}

is_usb_in(){
        return `dmesg |tail -100000|grep -i usb|wc -w`
}

while (true)
do
        if is_usb_in
        then
                echo "未检测到优盘，请重新插拔优盘。。"
        else
                echo "有新优盘插入。。。";
                if is_empty_dir /mnt
                then
                        echo " 还没挂载！正在执行挂载。。。";
                        #mount  /dev/sdb1 /media/kylin
                        touch lbwnb.txt
                        break
                else
                        echo "优盘已经挂载了！"
                fi
        fi
        sleep 3s
done