How Wake-On-LAN works (2020)(blog.xaner.dev)

  #!/bin/bash 
  mac="\\x${1//:/\\x}" 
  wol="\xFF\xFF\xFF\xFF\xFF\xFF" 
  for i in {1..16}; do wol+="$mac"; done 
  printf "$wol" > "/dev/udp/$2/9"

    // Given $macAddress and $addr and $port
    $macAddress = str_replace(":","",$macAddress);
    $macAddress = str_replace("-","",$macAddress);

    $header = pack('H12','FFFFFFFFFFFF');
    $payload = pack("H12",$macAddress);
    $packet = $header . str_repeat($payload,16);

    $sock = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
    socket_set_option($sock, 1, 6, TRUE);
    socket_sendto($sock, $payload, strlen($payload), 0, $addr, $port);
    socket_close($sock);