UnoFirmware

String message = "\"Temperature\": 25,\r\"Pressure\": 11,\r\"Light\": 1200";
String command = "";
char c;
uint8_t i = 0;

void getData(){
   Serial.print("{");
   Serial.print(message);
   Serial.print("}");
}

bool checkInput(){
   while(Serial.available()) {
        char c = (char)
        Serial.read();
        if ( c == '\r' || c == '\n') {
            return true;
        }
        command += c;
    }
    return false;
}
void setup(){
   Serial.begin(115200);
}

void loop(){
   if(checkInput()) {
      if ( String("getData") == command ){
         Serial.print("Detected\r");
         getData();
      }else{
         Serial.print("Not detected\r");
      }
      command = "";
   }
   delay(1000);
}