title: How to insert columns into a CSV file using awk
body: <p>I want to use sed to add some columns into the below csv file with default value.</p>
  
  <p>My file is like:</p>
  
  <pre><code>40,2012-05-30,London,61,Sunny
  41,2012-02-22,Moscow,11,Snow
  54,2012-04-10,Tokyo,02,Sunny
  </code></pre>
  
  <p>I want the output to be:</p>
  
  <pre><code>40,2012-05-30,NULL,London,NULL,NULL,61,Sunny,Tom
  41,2012-02-22,NULL,Moscow,NULL,NULL,11,Sunny,Tom
  54,2012-04-10,NULL,Tokyo,NULL,NULL,02,Sunny,Tom
  </code></pre>
  
  <p>What are the best sed or awk commands to get the desired output? </p>