title: How do I replace empty strings in a tsv with a value?
body: <p>I have a tsv, file1, that is structured as follows:</p>
  
  <pre><code>col1  col2  col3
  1     4     3
  22    0     8
  3           5
  </code></pre>
  
  <p>so that the last line would look something like <code>3\t\t5</code>, if it was printed out. I'd like to replace that empty string with 'NA', so that the line would then be <code>3\tNA\t5</code>. What is the easiest way to go about this using the command line?</p>