title: Is there a way to 'uniq' by column?
body: <p>I have a .csv file like this:</p>
  <pre><code>stack2@domain.example,2009-11-27 01:05:47.893000000,domain.example,127.0.0.1
  overflow@domain2.example,2009-11-27 00:58:29.793000000,domain2.example,255.255.255.0
  overflow@domain2.example,2009-11-27 00:58:29.646465785,domain2.example,256.255.255.0
  ...
  </code></pre>
  <p>I have to remove duplicate e-mails (the entire line) from the file (i.e. one of the lines containing <code>overflow@domain2.example</code> in the above example). How do I use <code>uniq</code> on only field 1 (separated by commas)? According to <code>man</code>, <code>uniq</code> doesn't have options for columns.</p>
  <p>I tried something with <code>sort | uniq</code> but it doesn't work.</p>