用php得到网卡mac

<?php
$command = escapeshellcmd("nbtstat -A " . $_SERVER["REMOTE_ADDR"]);
if (strtolower(substr(PHP_OS, 0, 3)) == "win")
{
exec($command, $result);
array_pop($result);
print substr(array_pop($result), 18);
}
else
{
print "THE OS IS NOT WINDOWS 2000";
}
?>