Linux的shell编程及语句的应用

#!/bin/bash
mkdir ./tmp/backup
for filename in $(ls)
do
cp $filename backup/$filename
if ($? -ne 0)
then echo "copy for $filename failed"
fi
done
这代码是要将当前目录下的所有东西拷贝到tmp 下的backup目录中（当前不在tmp 目录中）这里为什么无法运行,怎么修改，求详细解释

#!/bin/bash
mkdir ./tmp/backup
for filename in $(ls)
do
cp $filename backup/$filename #这里是拷贝到当前目录下的backup，应该写为cp $filename /tmp/backup/$filename
if ($? -ne 0)
then echo "copy for $filename failed"
fi
done