在学习Linux shell scripts时，一个最常见的错误就是用for（for line in $(cat file.txt) do …）循环逐行读取文件。下面的例子可以看出这样做的结果。
文件file.txt内容：
cat file.txt
This is the row No 1;
This is the row No 2;
This is the row No 3.
用for循环的例子：
for line in $(cat file.txt); do echo $line; done
This
is
the
row
No
1;
This
is
the
row
No
2;
[…]
显然这并不是我们想要的效果。解决方案是采用带内部读取的while循环。
while循环是用来逐行读取文件最恰当且最简单的方法：
while read line; do echo $line; done < file.txt
This is the row No 1;
This is the row No 2;
This is the row No 3.