title: how to look for a string on a file and get its line number
body: <p>Good day all,</p>
  
  <p>I need you guys assistance on this problem I can't figure out how to go around this at the moment.
  I have a file that contains dates in the format below.<br>
  03\03\2010</p>
  
  <p>04\03\2010</p>
  
  <p>05\03\2010</p>
  
  <p>06\03\2010</p>
  
  <p>07\03\2010</p>
  
  <p>08\03\2010</p>
  
  <p>09\03\2010</p>
  
  <p>10\03\2010 <br>
  . . .<br>
  . . .<br>
  . . .<br>
  I want to get the line number of any specified date string from the file.
  That is if I want to get the line number of 09\03\2010 how can I achieve this.</p>