title: awk regex can't match ip addresses when trying to find repeating digits
body: <p>I can't get the following to match any IP addresses</p>
  
  <pre><code>awk '/[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}/{print $0}' maillog
  </code></pre>
  
  <p>or this one...</p>
  
  <pre><code>awk '/[[:digit:]]{1,3}\.[[:digit:]]{1,3}\.[[:digit:]]{1,3}\.[[:digit:]]{1,3}/' maillog
  </code></pre>
  
  <p>but this works... </p>
  
  <pre><code>awk '/127.0.0.1/{print $0}' maillog
  </code></pre>
  
  <p>and so does this...</p>
  
  <pre><code>awk '/[0-9]+\.[0-9]+\.[0-9]+\.[0-9]/{print $0}' maillog
  </code></pre>
  
  <p>What am I doing wrong in the first two?</p>