Update Emacs packages on the command line

update_packages.sh

#!/bin/sh

emacs --batch -l ~/.emacs \
      --eval="(progn (require 'package) \
                     (package-initialize) \
                     (package-refresh-contents) \
                     (mapc (lambda (pkg)
                             (let* ((new (cadr (assq pkg package-archive-contents)))
                                    (installed (cadr (assq pkg package-alist))))
                               (when (and new installed
                                          (version-list-< (package-desc-version installed)
                                                          (package-desc-version new)))
                                 (package-install new))))
                           (mapcar 'car package-alist)))"