title: how to merge huge amount of files without creating a new file
body: <p>I'm trying to merge a huge amount of files which total size is 75Gb. If I use, e.g.</p>
  
  <p><code>~$ cat * &gt; out.merge
  </code></p>
  
  <p>The size of the two files amounts to 150Gb and my HD has not such space. So how to avoid duplicate the data?</p>
  
  <p>Thanks in advance...</p>