假设读取的文件为当期目录下的 test.txt 文件，内容如下：
Google Runoob Taobao
实例 1
#!/bin/bash
while read line
do
echo $line
done < test.txt
执行输出结果为：
Google Runoob Taobao
实例 2
#!/bin/bash
cat test.txt | while read line
do
echo $line
done
执行输出结果为：
Google Runoob Taobao
实例 3
for line in `cat test.txt`
do
echo $line
done
执行输出结果为：
Google Runoob Taobao
for 逐行读和 while 逐行读是有区别的，如:
$ cat test.txt
Runoob
Taobao
$ cat test.txt | while read line; do echo $line; done
Runoob
Taobao
$ for line in $(<test.txt); do echo $line; done
Runoob
Taobao
