title: regular expression exclude string NO LOOKAHEAD/LOOKBEHIND allowed
body: <p>I need to exclude 2 different strings in <strong>filezilla</strong> but I can <strong>NOT</strong> use lookaheads/lookbehinds
  I am looking through a massive number of files and I need to exclude filenames that contain 'immutable' (without the quotes of course) and ALSO exclude '.txt' (also without quotes) 
  I say again <strong>I can NOT use lookaheads/lookbehinds</strong> I cannot use '(?!' or '(!=' or '(?' at all. I have perused around here and found lots of answers that involve lookaheads (which again, I cannot use) and I've also found some interesting ones that I have tried but with no avail
  here are two examples I have tried:</p>
  
  <pre><code>(.+)([^i]|i[^m]|im[^m])(.+)([^\.]|\.[t]|\.t[^x])
  
  ([^i]*(i([^m]|$)|im([^m]|$)|imm([^u]|$)))*
  </code></pre>
  
  <p>I have tried multiple combinations of the above with and without extra () grouped around them. Also, there will be an arbitrary number of characters both before and after the string literal, 'immutable'... Please help y'all!</p>
  
  <p>P.S. I am highly aware that the following two work perfectly but <strong>filezilla does NOT accept them</strong></p>
  
  <pre><code>/^(?!.*immutable)(.*)((\.jpg)|(\.png)|(\.gif)|(\.jpeg))$/
  above matches any IMAGE file-name without immutable
  /^(?!.*immutable)(.*)$/
  above matches any FILE file-name without immutable
  </code></pre>
  
  <p>Here is what filezilla gives me when I try any normally working regex
  "Invalid regular expression 'my-reg-ex-here': quantifier operand invalid"</p>