The env is inherited using the values in both $_SERVER and $_ENV. getenv() is not used because it is not available in PHP 5.5, and it shouldn't be needed since either $_SERVER or $_ENV contain the env vars. If you modify these arrays, it's your responsibility to do it wisely I believe.

If I'm not mistaken, getenv() is around since PHP 4 😉

On the other hand, $_ENV is unavailable on production systems using php.ini-production. $_SERVER is though, I'm not sure why it's still not working for me. I'll do some more tests and update this issue.

getenv() with no arguments exists only since 7.1. $_SERVER also contains the env vars.

Snap, I missed that from the docs. Thanks for the clarification.

I think I traced it down to being an issue with PHPs built-in web server.

<?php
# test.php
var_dump($_SERVER);
var_dump($_ENV);
var_dump(getenv());

And run with php -S 0.0.0.0:88 test.php results in:

array(23) {
  ["DOCUMENT_ROOT"]
  // ... some more server vars, without env vars
}
array(0) {
}
array(62) {
  ["PATH"]
  // ... all env vars
}

A simple workaround for this would be (granted you're on PHP >= 7.1):

if (php_sapi_name() === "cli-server") {
    $_ENV = getenv();
}

Or running the server with php -S 0.0.0.0:88 -d variables_order=EGPCS test.php (source).