- 条件为真就进入循环，条件为假就退出循环
- 语法结构
```shell
while 表达式
do
	command
done
```

- 与read结合读取文件
```
me@me-EQ59:~/shell_demo/scripts/shell02$ ./while_read.sh
10.0.0.1
123
10.0.0.2
124
10.0.0.3
125
me@me-EQ59:~/shell_demo/scripts/shell02$ cat while_read.sh
#! /bin/env bash

while read ip pass
do
	echo $ip
	echo $pass
done < ip.txt
me@me-EQ59:~/shell_demo/scripts/shell02$ cat ip.txt
10.0.0.1 123
10.0.0.2 124
10.0.0.3 125
me@me-EQ59:~/shell_demo/scripts/shell02$
```