title: Delete a variable in awk
body: <p>I wonder if it is possible to delete a variable in <code>awk</code>. For an array, you can say <code>delete a[2]</code> and the index <code>2</code> of the array <code>a[]</code> will be deleted. However, for a variable I cannot find a way.</p>
  
  <p>The closest I get is to say <code>var=""</code> or <code>var=0</code>.</p>
  
  <p>But then, it seems that the default value of a non-existing variable is <code>0</code> or <code>False</code>:</p>
  
  <pre><code>$ awk 'BEGIN {if (b==0) print 5}'
  5
  $ awk 'BEGIN {if (!b) print 5}' 
  5
  </code></pre>
  
  <p>So I also wonder if it is possible to distinguish between a variable that is set to <code>0</code> and a variable that has not been set, because it seems not to:</p>
  
  <pre><code>$ awk 'BEGIN {a=0; if (a==b) print 5}'
  5
  </code></pre>