title: Pattern matching digits does not work in egrep?
body: <p>Why can't I match the string</p>
  
  <pre><code>"1234567-1234567890"
  </code></pre>
  
  <p>with the given regular expression</p>
  
  <pre><code>\d{7}-\d{10}
  </code></pre>
  
  <p>with <code>egrep</code> from the shell like this:</p>
  
  <pre><code>egrep \d{7}-\d{10} file
  </code></pre>
  
  <p>?</p>