source: 
http://php.net/manual/en/ref.sockets.php
http://www.rkrishardy.com/2009/12/permission-denied-13-when-opening-socket-in-php-apache/

<?php
/**
 * Wake-on-LAN
 *
 * @return boolean
 *   TRUE:    Socked was created successfully and the message has been sent.
 *   FALSE:   Something went wrong
 *
 * @param string|array  $mac   You will WAKE-UP this WOL-enabled computer, you
 *                             need to add the MAC-address here. Mac can be
 *                             array too.
 *
 * @param string|array  $addr  You will send and broadcast to this address.
 *                             Normally you need to use the 255.255.255.255
 *                             address, so I made it as the default. You don't need to do anything with this.
 *                       
 *                             If you get permission denied errors when using
 *                             255.255.255.255 have permission denied problems
 *                             you can set $addr = false to get the broadcast
 *                             address from the network interface using the
 *                             ifconfig command.
 *
 *                             $addr can be array with broadcast IP values
 *
 * Example 1:
 *   When the message has been sent you will see the message "Done...."
 *   if ( wake_on_lan('00:00:00:00:00:00'))
 *      echo 'Done...';
 *   else
 *      echo 'Error while sending';
 */

function wake_on_lan($mac, $addr=false, $port=7) {
    if ($addr === false){
        exec("ifconfig | grep Bcast | cut -d \":\" -f 3 | cut -d \" \" -f 1",$addr);
        $addr=array_flip(array_flip($addr));
    }
    if(is_array($addr)){
        $last_ret = false;
        for ($i = 0; $i < count($addr); $i++)
            if ($addr[$i] !== false) {
                $last_ret = wake_on_lan($mac, $addr[$i], $port);
            }
        return $last_ret;
    }
    if (is_array($mac)){
        $ret = array();
        foreach($mac as $k =< $v)
            $ret[$k] = wake_on_lan($v, $addr, $port);
        return $ret;
    }
    //Check if it's an real MAC-address and split it into an array
    $mac = strtoupper($mac);
    if (!preg_match("/([A-F0-9]{1,2}[-:]){5}[A-F0-9]{1,2}/", $mac, $maccheck))
        return false;
    $addr_byte = preg_split("/[-:]/", $maccheck[0]);
 
    //Creating hardware adress
    $hw_addr = '';
    for ($a = 0; $a < 6; $a++)//Changing mac adres from HEXEDECIMAL to DECIMAL
        $hw_addr .= chr(hexdec($addr_byte[$a]));
  
    //Create package data
    $msg = str_repeat(chr(255),6);
    for ($a = 1; $a <= 16; $a++)
        $msg .= $hw_addr;
    //Sending data
    if (function_exists('socket_create')){
        //socket_create exists
        $sock = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);    //Can create the socket
        if ($sock){
            $sock_data = socket_set_option($sock, SOL_SOCKET, SO_BROADCAST, 1); //Set
            if ($sock_data){
                $sock_data = socket_sendto($sock, $msg, strlen($msg), 0, $addr,$port); //Send data
                if ($sock_data){
                    socket_close($sock); //Close socket
                    unset($sock);
                    return true;
                }
            }
        }
        @socket_close($sock);
        unset($sock);
    }
    $sock=fsockopen("udp://" . $addr, $port);
    if($sock){
        $ret=fwrite($sock,$msg);
        fclose($sock);
    }
    if($ret)
        return true;
    return false;  
}

if (@wake_on_lan('00:00:00:00:00:00')) {
    echo 'Done...';
} else {
    echo 'Error while sending';
}
?>