title: Merge all .txt files in all subdirectories in one txt file
body: <p>I want to merge content of all .txt files in my directory (containing subdirectories) to one txt file. 
  I need to do this:</p>
  
  <pre><code>xcopy text1.txt + text2.txt text3.txt
  </code></pre>
  
  <p>but in a for loop which takes all text files in current directory. i assume something like this:</p>
  
  <pre><code>for \r ___ in ___ do copy list.txt
  </code></pre>
  
  <p>Thanks in advance.</p>