(defun cperl-save-buffer (&optional args)
  (interactive "p")
  (if (buffer-modified-p)
      (perltidy-buffer))
  (save-buffer t))
(defun perltidy-buffer ()
  (interactive)
  (save-excursion
    (shell-command-on-region
     (point-min) (point-max)
     "perltidy -st" nil t shell-command-default-error-buffer)))
(add-to-list
  'cperl-mode-hook
  (lambda ()
    (substitute-key-definition 'save-buffer 'cperl-save-buffer cperl-mode-map global-map)))