title: add the contents of 2 txt files together
body: <p>I have this small piece of code on my website that i use to count downloads.
  its pretty simple really,
  counter.php sends the command and counter.txt is just a 1 line text file with a number that auto goes up every time the link is clicked.</p>
  
  <p>My question is, is it possible to have 2 counter.txt files and add them to a third counter.txt file?  so it would look something like:
  counter.txt + counter2.txt = counter3.txt ?</p>
  
  <pre><code>$counter = 'counter.txt'; 
  $download = 'downloadurlhere';
  
  $number = file_get_contents($counter); // read count file 
  $number++; // increment count by 1 
  $fh = fopen($counter, 'w'); // open count file for writing 
  fwrite($fh, $number); // write new count to count file 
  fclose($fh); // close count file 
  header("Location: $download"); // get download 
  </code></pre>
  
  <p>So essentially i want to offer 2 downloads
  a light version and a full version</p>
  
  <p>and then keep track of each download count separately.  but then also have a count for the total of both downloads.</p>
  
  <p>oh and to make sure i include enough detail, on the download.php page i echo the counter.txt file with</p>
  
  <pre><code>&lt;?php echo file_get_contents('counter.txt');?&gt;
  </code></pre>