here's a function for determining how many emacs packages (using emacs 24 package system) are ready to upgrade. this is suitable for execution in batch-mode, perhaps as part of a script that routes output to a system-wide notification

package-check.el

(require 'package)
(add-to-list 'package-archives '("org" . "http://orgmode.org/elpa/") t)
(add-to-list 'package-archives '("melpa" . "http://melpa.milkbox.net/packages/" ))
;(package-initialize) ;; trigger elpa packages

(defun get-updatable-count ()
  (let (old-archives new-packages)
    ;; Read the locally-cached archive-contents.
    (package-read-all-archive-contents)
    (setq old-archives package-archive-contents)
    ;; Fetch the remote list of packages.
    (package-refresh-contents)
    ;; Find which packages are new.
    (dolist (elt package-archive-contents)
      (unless (assq (car elt) old-archives)
        (push (car elt) new-packages)))
    (let ((buf (get-buffer-create "*Packages*")))
      (with-current-buffer buf
        (with-current-buffer buf
          (package-menu-mode)
          (set (make-local-variable 'package-menu--new-package-list)
               new-packages)
          (package-menu--generate nil t)))))
  (with-current-buffer "*Packages*"
    (let ((lst (package-menu--find-upgrades)))
      (print (apply 'concat
                    (append 
                     (list (format "%d packages can be updated:\n" (length lst)))
                     (mapcar
                      (lambda (s) (format "%s\n" (car s)))
                      lst)))))))