Mounting a folder in a phar doesn't work - php

Question

I've created a phar of a Symfony2 web application, but I'm having some troubles with the cache-folders.
I found out that I could mount an external file/folder into a phar. That would fix my issue, but I can't get the example on the PHP site working.
I have a phar which contains an index.php:
<?php
$configuration = simplexml_load_string(file_get_contents(
Phar::running(false) . '/config.xml'));
?>
Then I include the .phar with the following code:
<?php
// first set up the association between the abstract config.xml
// and the actual one on disk
Phar::mount('phar://config.xml', '/var/www/$projectname/config.xml');
// now run the application
include 'phar-archive.phar';
?>
All files exists, but I get the following error:
PHP Fatal error: Uncaught exception 'PharException' with message 'config.xml is not a phar archive, cannot mount' in /var/www/$projectname/index.php:3
I already tried relative/absolute paths, changing permissions but can't get this to work. Additionally a working example of how I could mount a folder into a phar would be great !

Answer 1

First check that variable $projectname exist in this place (just run echo $projectname; before Phar::mount). If all ok, then change
Phar::mount('phar://config.xml', '/var/www/$projectname/config.xml');
to
Phar::mount('phar://config.xml', "/var/www/{$projectname}/config.xml");
It seems that variable $projectname not converted to its value because you used single quotes.