title: FINDSTR Command Ignoring Regex
body: <p>I'm searching for urls in a html file using the following in command prompt</p>
  
  <p><code>findstr /r "//i\.4cdn\.org/pol/\d+\.(?:png|jpg|jpeg|webm|gif)" pol.html</code></p>
  
  <p>The regex works fine in a Notepad++ search, however when I run it with the <code>findstr</code> command it returns it's help page and this:</p>
  
  <pre><code>FINDSTR: // ignored
  FINDSTR: /\ ignored
  FINDSTR: /. ignored
  FINDSTR: /4 ignored
  FINDSTR: /c ignored
  FINDSTR: /d ignored
  FINDSTR: /\ ignored
  FINDSTR: /. ignored
  FINDSTR: /g ignored
  FINDSTR: // ignored
  FINDSTR: // ignored
  FINDSTR: /\ ignored
  FINDSTR: /d ignored
  FINDSTR: /+ ignored
  FINDSTR: /\ ignored
  FINDSTR: /. ignored
  FINDSTR: /( ignored
  </code></pre>
  
  <p>I'm pretty new to regex so if there's something wrong in there, sorry in advance.</p>