判斷密碼是否正確

#!/bin/bash
str="sc30"
for ((i=1;i<=3;i++));do
read -p "請輸入第$i次密碼：" sc
if [ $sc ]; then
if [ $sc = $str ];then
echo "密碼輸入正確"; break
fi
else
echo "密碼輸入錯誤，第$i次"
fi
done