title: Duplicate each line in a text file
body: <p>I would like to dupliacte lines in a folder with multiples txt files, including the blank lines. A batch command would be ideal or python drag&amp;drop script.
  Here is an example. (x being blank line)</p>
  <pre><code>Alfred
  x
  Britney
  </code></pre>
  <p>And I need it like this.</p>
  <pre><code>Alfred
  Alfred
  x
  x
  Britney
  Britney
  </code></pre>
  <p>As you can see, each line is doubled even the lines where there are no texts.
  How can that be done please ?</p>