title: Make grep stop after first NON-matching line
body: <p>I'm trying to use grep to go through some logs and only select the most recent entries.  The logs have years of heavy traffic on them so it's silly to do </p>
  
  <pre><code>    tac error.log | grep 2012
      tac error.log | grep "Jan.2012" 
  </code></pre>
  
  <p>etc.</p>
  
  <p>and wait for 10 minutes while it goes through several million lines which I already know are not going to match.  I know there is the <code>-m</code> option to stop at the first match but I don't know of a way to make it stop at first non-match.  I could do something like <code>grep -B MAX_INT -m 1 2011</code> but that's hardly an optimal solution.</p>
  
  <p>Can grep handle this or would awk make more sense?</p>