PHP SimpleXML XPath查询

I have a function which is trying to get text from XML using XPath query.The function reads:

function getInterviewText($id)  {
    $sxe = simplexml_load_file("./interview2.xml");
    foreach($sxe->xpath('//interview') as $item) {
        $row = simplexml_load_string($item->asXML());
        $v = $row->xpath('//interview-id[.="$id"]');
        if($v[0]) {
            echo '<interview-text>'.$item->INTERVIEW-TEXT.'</interview-text>' 
        }
    }
}

The XML File reads:

<?xml version="1.0"?>
<ROOT>
    <interview>
        <interview-id>1</interview-id>
        <INTERVIEW-TEXT>                                
            Test1
        </INTERVIEW-TEXT>
    </interview>
    <interview>
        <interview-id>2</interview-id>
        <INTERVIEW-TEXT>                              
            Test2          
        </INTERVIEW-TEXT>
    </interview>
</ROOT>

However, the function is not returning anything, when I am trying to call it with id=1 or 2. Any help is greatly appreciated.

Thanks

The problem is here:

$v = $row->xpath('//interview-id[.="$id"]');

$id is not being expanded because you are within a single-quoted string. Try one of the following instead:

$v = $row->xpath('//interview-id[.="' . $id . '"]');
// Or
$v = $row->xpath("//interview-id[.=\"{$id}\"]");