title: Get line number that contains a string
body: <p>How to get a line number that contains a specified string in a text file?</p>
  
  <p>Example text file contains:</p>
  
  <blockquote>
    <p>Red<br>
    White<br>
    Yellow<br>
    Green<br></p>
  </blockquote>
  
  <p>How to get "Yellow" line number? and can i write a string in a specified line, lets say i want to write a string in line 2?</p>