Replacing every empty line with a string, i.e. inserting strings to empty lines

Question

Given that I have a file such as

Lorem


Ipsum

Dolor

I want to insert strings (here, the % character) to those empty lines to obtain

Lorem
%
%
Ipsum
%
Dolor

How can I do this? I tried to follow a way similar to the methods defined here without success.

Answer 1

Try this:

(defun filibuster (str)
  (interactive "sString: ")
  (save-excursion
    (goto-char (point-min))
    (while (re-search-forward "^$" nil t)
      (replace-match str))))

Answer 2

@abo-abo gave the Lisp answer. You don't specify whether you want to do this from Lisp or interactively. Interactively, you can do what you ask in either of these ways:

• M-x replace-regexp RET ^$ RET % RET

• C-M-% RET ^$ RET % RET !