(defun perltidy ()
  "Run perltidy on the current region or buffer."
  (interactive)
  (save-excursion
    (unless mark-active (mark-defun))
    (shell-command-on-region (point) (mark) "perltidy --profile=/home/foo/.perltidyrc -q" nil t)))

(global-set-key [(f5)] 'perltidy)