title: Concat all files in directory tree into single file with paths separators
body: <p>As example, I have the following structure</p>
  
  <pre><code>mydir/a/fileA.txt
  mydir/b/fileB.js
  mydir/fileC.js
  </code></pre>
  
  <ul>
  <li>fileA.txt content: <code>Im file A</code></li>
  <li>fileB.txt content: <code>Im file B</code></li>
  <li>fileC.txt content: <code>Im file C</code></li>
  </ul>
  
  <p>And I want to concat content of all files in <code>mydir</code> directory (recursively) into <code>output.txt</code> - line before each file content there shoud be included this separator (as first line) <code>---next-file-&gt;&gt;&gt;:</code> and path to this file (starting from mydir/..) wrapped by new lines. So the desired output for above example should be </p>
  
  <pre><code>---next-file-&gt;&gt;&gt;: mydir/a/fileA.txt
  
  Im file A
  
  ---next-file-&gt;&gt;&gt;: mydir/b/fileB.js
  
  Im file B
  
  ---next-file-&gt;&gt;&gt;: mydir/fileC.js
  
  Im file C
  </code></pre>
  
  <p>I tried the below code but don't have any idea how to include separators with each file path</p>
  
  <pre><code>find mydir/ -exec cat {} \; &gt; output.txt
  </code></pre>