A better alternative is to use emacs itself to manage, install and update all the required extra code. The ELPA project provides a way to install packages from different repositories, while el-get can help you declare recipes to install and update code from ELPA, or even Github or Emacswiki.

First, let’s setup some code that tries to load ELPA and el-get, and installs them if they are not present.

; derived from ELPA installation
; http://tromey.com/elpa/install.html
(defun eval-url (url)
  (let ((buffer (url-retrieve-synchronously url)))
  (save-excursion
    (set-buffer buffer)
    (goto-char (point-min))
    (re-search-forward "^$" nil 'move)
    (eval-region (point) (point-max))
    (kill-buffer (current-buffer)))))

;; Load ELPA
(add-to-list 'load-path "~/.emacs.d/elpa")

(defun install-elpa ()
  (eval-url "http://tromey.com/elpa/package-install.el"))

(if (require 'package nil t)
    (progn
      ;; Emacs 24+ includes ELPA, but requires some extra setup
      ;; to use the (better) tromey repo
      (if (>= emacs-major-version 24)
          (setq package-archives
                (cons '("tromey" . "http://tromey.com/elpa/")
                package-archives)))
      (package-initialize))
  (install-elpa))

;; Load el-get
(add-to-list 'load-path "~/.emacs.d/el-get/el-get")

(defun install-el-get ()
  (eval-url
   "https://github.com/dimitri/el-get/raw/master/el-get-install.el"))

(unless (require 'el-get nil t)
  (install-el-get))

Note that when using emacs 24, package.el is distributed with emacs but it points to the GNU package repository; the code above adds tromey’s more complete ELPA repository to the sources.

Unfortunately, the ELPA installer script appends a snippet of code to the end of the ~/.emacs file to auto-load package.el on startup. To avoid any problem, it is best to manually remove that code any only keep the load-or-install code above.

Now that ELPA and el-get are setup, we can declare all the packages we want installed. They will be installed the first time emacs is started, and simply loaded in the future.

; extra recipes for packages unknown to el-get (yet)
(setq el-get-sources
      '((:name css-mode :type elpa)
        (:name js2-mode-mooz
               :type git
               :url "git://github.com/mooz/js2-mode.git"
               :load "js2-mode.el"
               :compile ("js2-mode.el")
               :features js2-mode)))

; list all packages you want installed
(setq my-el-get-packages
      (append
       '(css-mode egg gist js2-mode-mooz)
       (mapcar 'el-get-source-name el-get-sources)))

(el-get 'sync my-el-get-packages)

The el-get 'sync call does all the magic, based on all the packages past in argument (as my-el-get-packages). Any packages for which el-get has a recipe can be installed.

The el-get-sources variable allows to declare extra custom recipes for code to install. In the example above, css-mode is simply pulled from the ELPA repository, while js2-mode-mooz is fetched directly from Github.

Replicating this code in all your ~/.emacs files is a very easy and convenient way to bootstrap the same emacs environment on multiple hosts.