title: Regular Expression - 4 digits in a row, but can't be all zeros
body: <p>I am looking for a solution that can exclusively be done with a regular expression.  I know this would be easy with variables, substrings, etc.  </p>
  
  <p>And I am looking for PCRE style regex syntax even though I mention vim.</p>
  
  <p>I need to identify strings with 4 numeric digits, and they can't be all 0's.  So the following strings would be a match:</p>
  
  <pre><code>0001 
  1000 
  1234 
  0101
  </code></pre>
  
  <p>And this would not:</p>
  
  <pre><code>0000
  </code></pre>
  
  <p>This is a substring that will occur at a set location within a large string, if that matters; I don't think it should. For example </p>
  
  <pre><code>xxxxxxxxxxxx0001xxxxx
  xxxxxxxxxxxx1000xxxxx
  xxxxxxxxxxxx1234xxxxx
  xxxxxxxxxxxx0101xxxxx
  xxxxxxxxxxxx0101xxxxx
  xxxxxxxxxxxx0000xxxxx
  </code></pre>