title: Syncing Required Packages in Emacs
date: 2013-12-30 11:30
tags: emacs, wsu
summary: A simple way to keep Emacs packages synced across machines using package.el
---

I use Emacs on several different computers.  To keep my configuration
consistent across all of them, I do what many people do and made the
`~/.emacs.d` directory a
[git repository](https://github.com/davexunit/.emacs.d).  I don’t like
to keep copies of all of the Elisp extensions that I use, such as
paredit and geiser, in this repository.  Instead, I prefer to use
package.el (introduced in Emacs 24) with the
[MELPA](https://melpa.org) repository.  This saves me from having to
manually keep all of the extensions I use up-to-date, but requires
another method to keep useful packages in sync between computers.

There’s a project called
[Pallet](https://github.com/rdallasgray/pallet) that solves this
problem, but it was too heavy for my liking.  Instead, I wrote a short
function that simply iterates over a list of required packages and
installs those that are not currently installed.

```elisp
;; Additional packages that I use.
(setq required-packages
      '(better-defaults
        elfeed
        geiser
        ido-ubiquitous
        js2-mode
        magit
        paredit
        rainbow-delimiters
        smex))

(defun install-missing-packages ()
  "Install all required packages that haven’t been installed."
  (interactive)
  (mapc (lambda (package)
          (unless (package-installed-p package)
            (package-install package)))
        required-packages)
  (message "Installed all missing packages!"))
```

Now, it’s as easy as typing `M-x install-missing-packages RET` when
starting Emacs for the first time on a new computer to download all of
the extensions that I need.  Note that before calling
`install-missing-packages` you must have already initialized the
package manager via the `package-initialize` function.  This approach
does require some manual bookkeeping in order to keep the
`required-packages` list up-to-date with your workflow, but I haven’t
found it to be problematic.

Update: If this solution is too simplistic for you, you should check
out [use-package](https://github.com/jwiegley/use-package), which
reddit user [lunayorn](http://www.reddit.com/user/lunaryorn) pointed
out to me.  Thanks!

Check out the comments on
[reddit](http://www.reddit.com/r/emacs/comments/1u0xr4/quick_hack_syncing_required_packages_in_emacs/).