title: How to delete empty lines in a file using Emacs?
body: <p>In Emacs, how to remove all empty lines (including tabs and spaces) in file? </p>
  
  <p>Can <code>M-x replace-regexp</code> do the trick? </p>
  
  <p>I can find the empty lines with regexp: <strong>^[st]*$</strong>, but don't know how to replace it by deleting.</p>