title: Delete duplicate string with PowerShell
body: <p>I have got text file:</p>
  
  <pre><code>1 2 4 5 6 7
  1 3 5 6 7 8
  1 2 3 4 5 6
  1 2 4 5 6 7
  </code></pre>
  
  <p>Here first and last line are simmilar. I have a lot of files that have double lines. I need to delete all dublicate.</p>