php - Setup File .env in Slim Framework

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Solution:

From package readme file:

Using getenv() and putenv() is strongly discouraged due to the fact that these functions are not thread safe, however it is still possible to instruct PHP dotenv to use these functions. Instead of calling Dotenv::createImmutable, one can call Dotenv::createUnsafeImmutable, which will add the PutenvAdapter behind the scenes. Your environment variables will now be available using the getenv method, as well as the super-globals.

So the main method of getting these values is using $_ENV and $_SERVER super-global not getenv() function.

You should either try to retrieve the values like:

$db_name = $_ENV['DB_NAME'];

or load the .env file like the example provided in the package:

$dotenv = Dotenv\Dotenv::createUnsafeImmutable(__DIR__);
$dotenv->load();

Also, make sure you pass correct directory (the one that .env file resides in) as the parameter. That normally should not be in the same directory as index.php but the example code you provide implies you are putting both files in one directory.