String stringOne = "mensagem";

void setup() {
  Serial.begin(115200);
  Serial.setTimeout(30);
  Serial.println("enter text");
}

void loop() {
  if (Serial.available() > 0) {
    String stringTwo = Serial.readString();
    stringTwo.trim();
    if (stringOne == stringTwo) {
      Serial.println("This is a match!");
    } else {
      Serial.println("No cigar!");
    }
  }
}