Variable output doesn't work

[M4GN3T]

Hi guys,

I created a plugin/hook with the following code:

Product: vBulletin
Hook Location: global_start (also tried init_startup)
Subject: XPRank
Execution Order: 5
Plugin PHP code:

$gebruiker_id = 1;
$sql="SELECT `xp` FROM  `rank` WHERE  `userid` = '".$gebruiker_id."'";
$dataxp=mysql_query($sql)or die(mysql_error());

while($inhoud = mysql_fetch_array($dataxp)) {
$xprank = $inhoud['xp'];
}

In my header template i use the following:
{vb:raw xprank}

Result:
Doesn't work, even not when i create a variable like $phpecho="test echo"; and then use {vbraw: phpecho}. Nothing works. Does anyone has a idea how to fix this?