title: Append n number of 0's as the prefix of integer
body: <p>I have the following data in a CSV file.</p>
  
  <pre><code>2454,"dum my"
  12345,"dummy"
  300001,"du m m y"
  </code></pre>
  
  <p>I was wondering, what regular expression I can use, to turn them into</p>
  
  <pre><code>002454,"dummy"
  012345,"dummy"
  300001,"dummy"
  </code></pre>
  
  <p>Thanks.</p>