Perl Code

# ==================================================================
# Perl script listens for the Arduino messages and displays them
#
# Windows 7, ActivePerl (32 bit)
# install win32::SerialPort module
#
# Based on: http://www.windmeadow.com/node/38
# ==================================================================

use strict;
use warnings;

require Win32::SerialPort;

# setup the serial port on the USB FTDI driver

my $portname = "COM4";

my $port = Win32::SerialPort->new($portname)
           or die "Can't open serial port (" . $portname . ")\n$^E\n";

$port->initialize();
$port->databits(8);
$port->baudrate(9600);
$port->parity("none");
$port->stopbits(1);
$port->debug(0);

# print "Serial port baudrate: " . $port->baudrate() . "\n";

# define line termination for $port->lookfor()
# Note: Arduino serial.println terminates each line/string sent with a "\r\n"

$port->are_match("\r\n");

my $data;

while(1)
{
   # poll looking for data

   $data = $port->lookfor();

   # -------------------------------------------------------------------
   # the default EOL for $port->lookfor() is "\n".  it is removed by the
   # method. to remove the remaining "\r" use  $data =~ s/\r$//;
   # -------------------------------------------------------------------

   # if we get data, display it

   if ($data)
   {
      print "String length:    " . length($data) . "\n";
      print "String Received: (" . $data . ")\n";
   }

   # sleep for a second (look up usleep for a shorter period)

   sleep(1);
}

Arduino code

// ======================================================
// Send "Hello World" message from the Arduino
// to the computer
// ======================================================

const int led = 13;                // led pin

void setup()
{                
   pinMode(led,OUTPUT);            // pic OUTPUT  
   Serial.begin(9600);             // set port baud rate
}

void loop()
{
   Serial.println("Hello World");  // send message
   flash(500);                     // flash led (milliseconds)
   delay(4000);                    // pause (milliseconds)
}

void flash(int duration)
{
   digitalWrite(led,HIGH);
   delay(duration);
   digitalWrite(led,LOW);
   delay(duration);
}