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$_ENV['username'] = 'admin';
Environment variables are valid in all pages, so is the environment username stored in memory or in a file?
Internally in PHP, variables are stored in a container called zval
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
Internally in PHP, variables are stored in a container called zval