Is it better to use require_once('filename.php') or require_once 'filename.php';

Question

Is this just a stylistic difference, or does using require_once('filename.php') vs require_once 'filename.php' have actual load/efficiency differences?

Answer 1

It's exactly the same thing. It's a matter of style.

The parentheses may get in the way some times. For instance, this example from the manual doesn't do what you expect:

if (include('vars.php') == 'OK') {
    echo 'OK';
}

See example #4.