get http headers values

<?php 			
// GET HTTP HEADERS VALUES
// SINGLE VALUE - Replace XXXXXX_XXXX with the name of the header you need in UPPERCASE (and with '-' replaced by '_')
$headerStringValue = $_SERVER['HTTP_XXXXXX_XXXX'];
echo $headerStringValue;
// GET ALL HEADERS			
$headers = apache_request_headers();
foreach ($headers as $header => $value) {
    echo "$header: $value <br />\n";
} ?>