title: "Event not found" error for shell command in unix
body: <p>when i am trying to remove  consecutive duplicate lines  with</p>
  
  <p><code>awk "!x[$0]++" file</code></p>
  
  <p>its reporting <code>x[: Event not found.</code></p>
  
  <p>even the same case with</p>
  
  <p><code>sed -i -e "$!N; /^\(.*\)\n\1$/!P;D" file</code>   as well reporting</p>
  
  <p><code>N: Event not found.</code>
  i tried with single quotes too, it didn't help</p>
  
  <p>Any idea to fix those </p>