PHP script to receive JSON from Amazon Echo and run a simple on/off script (with thanks to Ghostbit for the original code https://gist.github.com/ghostbitmeta/824474ceea327da629c7)

echo.php

<?php

$EchoJArray = json_decode(file_get_contents('php://input'));
$RequestType = $EchoJArray->request->type;

$JsonOut 	= GetJsonMessageResponse($RequestType,$EchoJArray);
$size 		= strlen($JsonOut);
header('Content-Type: application/json');
header("Content-length: $size");
echo $JsonOut;


function GetJsonMessageResponse($RequestMessageType,$EchoJArray){

  // Variable to confirm everything was successful;
  $pass = True;

  // ******************** Get state ********************;
  $action = $EchoJArray->request->intent->slots->power->value;
  if(empty($action)) {
    $action = "off";
  }
  // ******************** Execute ********************;
  if($pass){
    $cmd = "/home/pi/alexa/heater.py";
    
    switch ($action) {
      
    case 'on':
      $output=shell_exec("$cmd -n");
      break;
      
    case 'off':
      $status = shell_exec("$cmd -f");
      break;
    }
  }
// ******************** Responses ********************;
  if ($pass and $action=="off") {
    $text_title = "Turning shack heater off";
    $text_response = "The shack heater is now off";
    $voice_response = "The shack heater is now off";
    $voice_reprompt = "";
  } 
  if ($pass and $action=="on") {
    $text_title = "Turning shack heater on";
    $text_response = "The shack heater is now on";
    $voice_response = "The shack heater is now on";
    $voice_reprompt = "";
  } 

  // ******************** JSON reply built below ********************;
  $RequestId = $EchoJArray->request->requestId;
  $ReturnValue = "";
  
  if( $RequestMessageType == "LaunchRequest" ){
    $ReturnValue= '
		{
		  "version": "1.0",
		  "sessionAttributes": {
			"countActionList": {
			  "read": true,
			  "category": true,
			  "currentTask": "none",
			  "currentStep": 0
			}
		  },
		  "response": {
			"outputSpeech": {
			  "type": "PlainText",
			  "text": "Done."
			}
		  },
                  "card": {
			  "type": "Simple",
			  "title": "' . $text_title . '",
			  "content": "' . $text_response . '"
			}
		}';
  }
  
  if( $RequestMessageType == "SessionEndedRequest" )
    {
      $ReturnValue = '{
		  "type": "SessionEndedRequest",
		  "requestId": "$RequestId",
		  "timestamp": "' . date("c") . '",
		  "reason": "USER_INITIATED "
		}
		';
      
    }
  
  if( $RequestMessageType == "IntentRequest" ){
    
    $ReturnValue= '
		{
		  "version": "1.0",
		  "sessionAttributes": {
			"countActionList": {
			  "read": true,
			  "category": true,
			  "currentTask": "none",
			  "currentStep": 0
			}
		  },
		  "response": {
			"outputSpeech": {
			  "type": "PlainText",
			  "text": "' . $voice_response . '"
			},
			"card": {
			  "type": "Simple",
			  "title": "' . $text_title . '",
			  "content": "' . $text_response . '"
			},
                        "reprompt": {
			  "outputSpeech": {
				"type": "PlainText",
				"text": "' . $voice_reprompt . '"
			  }
			},
                   "shouldEndSession": true
		  }
		
		}';
  }
  return $ReturnValue;
}

?>