;; Display trailing whitespace (use a very very light color)
(defun my-turn-on-show-trailing-whitespace ()
  "Set `show-trailing-whitespace' to t."
  (setq show-trailing-whitespace t))

(mapc (lambda (hook)
        (add-hook hook 'my-turn-on-show-trailing-whitespace))
      '(cperl-mode-hook))