使用PHP从file.tar中提取文件夹内容

I am trying to extract the contents of a folder within a tarball using PHP. I am using the following PHP to download and extract the archive:

<?php

function wget($address,$filename) {
    file_put_contents($filename,file_get_contents($address));
}

$newdir = 'test';

echo '<br>Downloading latest gzipped WordPress tarball';

wget('http://wordpress.org/latest.tar.gz', 'latest.tar.gz');

echo '<br>about to Extract from gz';

// decompress from gz
$p = new PharData('latest.tar.gz');
$p->decompress(); // creates files.tar

echo '<br>Extracted from gz';

// unarchive from the tar
$phar = new PharData('latest.tar');
echo '<br>Un-TARd';
$phar->extractTo($newdir); 

echo '<br>Complete';


?>

My problem is that this script extracts the tarball into /test/wordpress whereas I need it to extract to /test/. I have read through this documentation on the PHP.net Manual and replaced part of my code to meet one of the examples there. The code I had was:

$phar->extractTo($newdir);

And I changed that to:

$phar->extractTo($newdir, 'wordpress');

But that didn't work. The PHP script processed through to the end but the /test/ directory was empty. The aim of this is to create a one-click WordPress install on our local dev server.