title: How to find single entries in a txt file?
body: <p>I have a txt file with 12 columns. Some lines are duplicated and some are not. As an example i copied to first 4 columns of my data.</p>
  
  <pre><code>0       0       chr12   48548073  
  0       0       chr13   80612840
  2       0       chrX    4000600 
  2       0       chrX    31882528 
  3       0       chrX    3468481 
  4       0       chrX    31882726
  4       0       chr3    75007624
  </code></pre>
  
  <p>Based on the first column, you can see that some there are duplicates except entry '3'.
  I would like to print the only single entries, in this case '3'.</p>
  
  <p>The output will be</p>
  
  <pre><code>3       0       chrX    3468481
  </code></pre>
  
  <p>IS there a quick way of doing this with awk or perl? I can only think of using for loop in perl but given the fact that i have around 1.5M entries it will probably take some time.</p>