title: Regular expression - how to match string not starting with
body: <p>I have the following Strings:</p>
  
  <pre><code>abc 12x15x2x99 31x15x29 zzz
  ppp 12x52x2x69 24x05x59 mmm
  12x55x2x99 2x05x90
  12x55x2x99 20x05x71 zzz
  pppppp 12x55x2x17 21x55x99 
  21x4x23
  eee 24x45x49 mmmm
  </code></pre>
  
  <p>In each row I want to find match for NNxNNxNN where NN can be one number or two numbers</p>
  
  <p>I look for a string that not start and end with x and has the form NNxNNxNN</p>
  
  <p>I wrote the following RegEx, but it doesn't find the required match :</p>
  
  <pre><code>.*[^x]?([0-9]{1,2}x[0-9]{1,2}x[0-9]{1,2}[^x]).*
  </code></pre>
  
  <p>How can I tell it to not expect the symbol x at the beginning of the match?</p>