title: tail a log file from a specific line number
body: <p>I know how to tail a text file with a specific number of lines,</p>
  
  <pre><code>tail -n50 /this/is/my.log
  </code></pre>
  
  <p>However, how do I make that line count a variable?</p>
  
  <p>Let's say I have a large log file which is appended to daily by some program, all lines in the log file start with a datetime in this format:</p>
  
  <pre><code>Day Mon YY HH:MM:SS
  </code></pre>
  
  <p>Every day I want to output the tail of the log file but only for the previous days records. Let's say this output runs just after midnight, I'm not worried about the tail spilling over into the next day.</p>
  
  <p>I just want to be able to work out how many rows to tail, based on the first occurrence of yesterdays date...</p>
  
  <p>Is that possible?</p>