get-client-macaddress.php

<?php

$ipAddress=$_SERVER['REMOTE_ADDR'];

$matches=array();

echo 'IP:' . $ipAddress . '<br>';

# Execute arp
$arp=`arp -a $ipAddress`;

# Parsing MAC address from arp result
preg_match('/([a-fA-F0-9]{2}:){5}[a-fA-F0-9]{2}/', $arp, $matches);

# MAC address will be stored at index 0 of the array
echo 'MAC Address: ' . $matches[0];

?>