None of the posix_* functions are available under Windows, since Windows is not POSIX compliant. But there seems to be / was an optional software package available, see here: https://en.wikipedia.org/wiki/Microsoft_POSIX_subsystem
(PHP 4, PHP 5, PHP 7)
posix_getuid — Return the real user ID of the current process
Return the numeric real user ID of the current process.
Returns the user id, as an integer
Example #1 Example use of posix_getuid()
<?php
echo posix_getuid(); //10000
?>
None of the posix_* functions are available under Windows, since Windows is not POSIX compliant. But there seems to be / was an optional software package available, see here: https://en.wikipedia.org/wiki/Microsoft_POSIX_subsystem
Note that this function is not defined on Windows PHP.