Changeable configuration in php

conf.php

<?php
global $conf;
if (!isset($conf)) {
    $pathTemplate = dirname(__FILE__) . '/conf_%s.php';
    $configFile = sprintf($pathTemplate, 'script');
    $currentConfigFile = sprintf($pathTemplate, gethostname());
    if (file_exists($currentConfigFile)) {
        $configFile = $currentConfigFile;
    } elseif (array_key_exists('HTTP_HOST', $_SERVER)) {
        $currentConfigFile = sprintf($pathTemplate, $_SERVER['HTTP_HOST']);
        if (file_exists($currentConfigFile)) {
            $configFile = $currentConfigFile;
        } else {
            $configFile = sprintf($pathTemplate, 'localhost');
        }
    }
    $conf = require $configFile;
}

return $conf;

conf_localhost.php

<?php
return array(
    "conf_key" => "this is localhost."
);

conf_script.php

<?php
return array(
    "conf_key" => "this is script."
);

conf_test.com.php

<?php
return array(
    "conf_key" => "this is test.com."
);

test_localhost.php

<?php
$_SERVER['HTTP_HOST'] = 'localhost';
$conf = require 'conf.php';
echo $conf["conf_key"];  // this is localhost.

test_script.php

<?php
$conf = require 'conf.php';
echo $conf["conf_key"];  // this is script.

test_test.com.php

<?php
$_SERVER['HTTP_HOST'] = 'test.com';
$conf = require 'conf.php';
echo $conf["conf_key"];  // this is test.com.