DIRECTORY_SEPARATOR can actually be used /well, windows also supports it

Path separator, on Linux it is ‘/’ and on Windows it is ‘‘, I use /

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Path separator, on Linux it is ‘/’ and on Windows it is ‘‘, I use /

DIRECTORY_SEPARATOR is a predefined constant for path separator.
Determine its value based on the system your server is deployed on, or the system your PHP file is run on.
If it is a Linux system, its value is /. If it is a Windows system, its value is .
The function of this constant is to ensure that in any system, the path you write can be accessed normally by that system.