[CarlitoBrigante]

It's not difficult - store your script's working directory in a constant/variable, chdir to the vBulletin working directory, call global.php, and then chdir back to your script directory.

Basically, just do this:

// vBulletin path (edit the value)
define('VBULLETIN_CWD','/var/www/vhosts/yourwebsite.com/httpdocs/');
// Do not edit anything below
// Your script path
define('YOURSCRIPT_CWD', (($getcwd = getcwd()) ? $getcwd : '.'));
// Switch to vBulletin directory
chdir(VBULLETIN_CWD);
// Call backend
require_once('./global.php');
// Switch back to your script directory
chdir(YOURSCRIPT_CWD);