title: Regexp for substitution of anything other than numbers and 'N/A'
body: <p>I have a string:</p>
  
  <pre><code>my $str = "asd na ann nna aannaa NA 10012 3212and123 complan-boy 
             NANANANA n/a n/a nn/a na/a n/a/a";
  </code></pre>
  
  <p>I am trying to write a regexp that will remove everything other than numbers and <code>N/A</code> or <code>NA</code>.</p>
  
  <p>For this I need to make <strong><em>negative</em></strong> of this regexp as <code>/(n\/a|na|\d+)/i</code>.</p>
  
  <p>I tried this regexp:</p>
  
  <pre><code>s/[^(na|n\/a|\d+)]//gi
  </code></pre>
  
  <p>which finally boils down to this:</p>
  
  <pre><code>s/[^\d+na()\/|]//ig;
  </code></pre>
  
  <p>What do I do?</p>