중복 require 되었을때

default.php

<?php

if (!isset($conf)) {
    $conf = 1;
}

$conf += 1;
return $conf;

exec.php

<?php

require 'default.php';
$conf = require 'file1.php';

if (!debug_backtrace()) {
    echo $conf;
}

file1.php

<?php

$conf = require 'default.php';

if (!debug_backtrace()) {
    echo $conf;
} else {
    return $conf;
}