Work around for USB CDC based Arduino. Arduino 'Serial Event' example does not work on USB CDC based arduino such as Leonard or DaVinci board.

SerialEvent_loop.ino

/*
  Serial Event example
 
 When new serial data arrives, this sketch adds it to a String.
 When a newline is received, the loop prints the string and 
 clears it.
 
 A good test for this is to try it with a GPS receiver 
 that sends out NMEA 0183 sentences. 
 
 Created 9 May 2011
 by Tom Igoe
 
 This example code is in the public domain.
 
 http://www.arduino.cc/en/Tutorial/SerialEvent
 
 */

String inputString = "";         // a string to hold incoming data
boolean stringComplete = false;  // whether the string is complete

void setup() {
  // initialize serial:
  Serial.begin(9600);
  // reserve 200 bytes for the inputString:
  inputString.reserve(200);
}

void loop_event() {
  if (Serial.available()) {
    char inChar = (char)Serial.read(); 
    inputString += inChar;
    if (inChar == '\n') {
      stringComplete = true;
    }
  }
}

void loop() {
  loop_event();

  if (stringComplete) {
    Serial.println(inputString); 
    // clear the string:
    inputString = "";
    stringComplete = false;
  }
}