title: Remove the duplicate lines from a file without sorting
body: <p>I am trying to remove the duplicate lines from a file without sorting in linux.</p>
  <p>I have tried the below command:</p>
  <pre><code> awk '!a[$0]++' file.tcl
  </code></pre>
  <p>But, it is throwing me an error:</p>
  <pre><code> a[: Event not found.
  </code></pre>
  <p>Can anyone tell why the command is not working?</p>
  <p>Note: I am not using bash as a shell.</p>
  <p>Thanks &amp; Regards,</p>
  <p>Parth.</p>