title: grep - removing a line that contains anything other than specified characters
body: <p>I'm trying to find a way to delete any lines that contain characters other than what I specify. For example if I specify the characters a,e,i,o,u,r,s,t and I have a list of words</p>
  
  <pre><code>rat
  tar
  set 
  meow 
  </code></pre>
  
  <p>Then "meow" should be deleted from the list because it contains the letters "m" and "w", which I haven't okayed. Any ideas?</p>