用bash解析XML属性

我需要使用纯bash脚本从XML文件中获取属性。

So I have the following XML file with a root element Group and lots of Person elements, every of them has id and username attributes. id is unique value for each element:

<?xml version="1.0" encoding="UTF-8"?>
<Group id="D_8"
       main="false">

    <Person id="P_0001"
            email="email0001@example.com"
            username="person_0001"
            password="pass_0001"
            active="true"/>

    <Person id="P_0002"
            email="email0002@example.com"
            username="person_0002"
            password="pass_0002"
            active="true"/>

    <!--  ...and hundreds of other Person elements ...  -->
</Group>

And I need to use bash script to extract the id and username attributes into some key-value structure:

P_0001=person_0001
P_0002=person_0002

检查了其他相关答案，但是大多数建议使用XMLlint之类的XML解析器。但是很遗憾，我没有将它们放在目标计算机上。

请提出如何实现这一目标。