Arduino Read Serial String

void setup() {
  Serial.begin(115200);

  pinMode(13, OUTPUT);
}

String command;

void loop() {
  if (Serial.available()) {
    char c = Serial.read();

    if (c == '\n') {
      parseCommand(command);
      command = "";
    }
    else {
      command += c;
    }

  }

}

void parseCommand(String com) {
  String part1;
  String part2;

  //PINON 13

  part1 = com.substring(0, com.indexOf(" "));

  part2 = com.substring(com.indexOf(" ") + 1);

  if (part1.equalsIgnoreCase("pinon")) {
    int pin = part2.toInt();

    digitalWrite(pin, HIGH);
  } else if (part1.equalsIgnoreCase("pinoff")) {
    int pin = part2.toInt();

    digitalWrite(pin, LOW);
  } else {
    Serial.println("Command Not Found");
  }

}