title: node.js "undefined" mysteriously appears
body: <p>I have the following node.js files:</p>
  
  <pre><code>//test.js:
  var hash=require('./hash');
  var sys=require('sys');
  
  sys.puts(hash.hash("asdf","asdf"));
  </code></pre>
  
  <p>and</p>
  
  <pre><code>//hash.js:
  var exec=require('child_process').exec;
  var sys=require('sys');
  
  exports.hash=function(data,hash_type){
          exec('pwd',function callback(error,stdout,stderr){
                  sys.puts(stdout);
          });
  }
  </code></pre>
  
  <p>When I do <code>node test.js</code>, I get the following output:</p>
  
  <pre><code>eamorr@Compaq6000:~/Desktop/simple-hash$ node test.js 
  undefined
  /home/hynese/Desktop/nodejs-simple-hash
  </code></pre>
  
  <p>Why am I getting "undefined"??? I'm really stuck here...</p>
  
  <p>Any help is greatly appreciated.</p>
  
  <p>Many thanks in advance,</p>