sub readXML{
	# create object
	$xml = new XML::Simple (KeyAttr=>[]);

	# read XML file
	$data = $xml->XMLin($config_path  . "sensors.xml");
}

sub writeValueXML{
	while(! (-x $config_path . "sensors.xml")){} 	#wait until other process finish writing the file
	system("sudo chmod 644 $config_path" . "sensors.xml");	#set permission for root to rw only (exclusive write)

  	my $output = new IO::File(">" . $config_path . "sensors.xml");
  	my $writer = new XML::Writer(OUTPUT => $output);
	my $flag = 0;;
	$count = 0;

  	$writer->startTag("Sensors");
	while($count < $DATANUM){
		#write xml values
  		$e = $data->{$sensor_type[$count]};
		
		$writer->startTag("$sensor_type[$count]");
		$writer->startTag("value");
		$writer->characters($vars[$count]);			
	 	$writer->endTag("value");
		$writer->startTag("threshold");
		$writer->characters($e->{threshold});			
	 	$writer->endTag("threshold");
		$writer->endTag("$sensor_type[$count]");
		
		if(($vars[$count]*1.0) > ($e->{threshold}*1.0)){	#*1 to force it to float type
			if (-e $config_path . "SensorAlert.txt" && !$flag){
				while(! (-x $config_path . "SensorAlert.txt")){} 	#wait until other process finish writing the file
				unlink($config_path . "SensorAlert.txt");	#set permission for root to rw only (exclusive write)
			}

			open WRITEFILE, "+>>", $config_path . "SensorAlert.txt";
			print WRITEFILE "$count:$vars[$count]\n";
		    close(WRITEFILE);

			$flag++;
		}
		$count++;
	}

	$e = $data->{Weather_Data_Interval};
	$writer->startTag("Weather_Data_Interval");
	$writer->startTag("value");
	$writer->characters($e->{value});			
 	$writer->endTag("value");	
	$writer->endTag("Weather_Data_Interval");

 	$writer->endTag("Sensors");
  	$writer->end();

  	$output->close();

	if($flag){
		read_config_file;
		if ($config_data[10] ne "Sensors:disabled\n"){
			$config_data[10] = "Sensors:true\n";
			write_config_file;
		}
		system("sudo chmod 777 $config_path" . "SensorAlert.txt");
	}
	system("sudo chmod 777 $config_path" . "sensors.xml");
}

sub appendLoggedFile{
	my ($second, $minute, $hour, $dayOfMonth, $month, $yearOffset, $dayOfWeek, $dayOfYear, $daylightSavings) = localtime();
	$year = 1900 + $yearOffset;
	my $theTime = "$hour:$minute:$second, $weekDays[$dayOfWeek] $months[$month] $dayOfMonth, $year";

  	open WRITEFILE, "+>>", $data_path . "$months[$month]_$dayOfMonth" . "_SensorLog.txt" or die $!;
    print WRITEFILE $values . ",\t\t" . $theTime . "\n";
    close(WRITEFILE);
}