(defun regex-render-ruby (regex sample)
  (with-temp-buffer
    (insert (format "
line = DATA.read
re = /%s/
print '('
pos = 0
while md=re.match(line,pos)
  printf '(%%d %%d', md.begin(0), md.end(0)-md.begin(0)
  puts
  md.captures.each_with_index{|c,i| printf '(%%d . %%s)', i+1,c.inspect }
  pos = md.end(0)
  puts ')'
end
print ')'
__END__
%s" regex sample))
    (insert (format ""))
   (call-process-region (point-min) (point-max) "ruby" t t)
   (goto-char (point-min))
   (read (current-buffer))))

(defun regex-tool-emacs ()
  (interactive)
  (setq regex-tool-backend 'emacs)
  (regex-tool))
(defun regex-tool-perl ()
  (interactive)
  (setq regex-tool-backend 'perl)
  (advice-remove 'regex-render-perl 'regex-render-ruby)
  (regex-tool))
(defun regex-tool-ruby ()
  (interactive)
  (setq regex-tool-backend 'perl)
  (advice-add 'regex-render-perl :override 'regex-render-ruby)
  (regex-tool))