title: grep character not followed by character
body: <p>I'm trying to print lines that have <code>b</code> not followed by <code>e</code> in a file. I tried using negative look-ahead, but it's not working.</p>
  
  <pre><code> grep  'b(?!e)' filename
   grep '(?!e)b)' filename
   egrep  'b(?!e)' f3.txt
  </code></pre>
  
  <p>When I run these commands, nothing shows up, no error or anything else. I checked other people's similar posts as well but was unable to run it.</p>