I want to automatically install packages that I don't have locally installed when I initialize Emacs. I use the following code to install some packages.

(mapc #'(lambda (pkg)
           (if (not (package-installed-p pkg))
                     (package-install pkg)))
             ; ...

However, when loading Emacs, Emacs says the package is not available for installation. However, it exists on the packages buffer.

error: Package `json-mode' is not available for installation

Does anyone know what I am doing wrong?

  • What is your value for package-archives? If you haven't MELPA to it yet, you might need to do that first before calling the code in your question: (add-to-list 'package-archives '("melpa" . "http://melpa.milkbox.net/packages/") t) – waymondo May 28 '15 at 14:58
  • @waymondo I have melpa, elpa, and marmalade set before this snippet – David May 28 '15 at 15:00
  • Related question, related solution. – Kaushal Modi May 28 '15 at 15:23

You most likely need a package-refresh-contents call to download the list of available packages first:

(defvar my-useful-packages
  '(ace-jump-mode ace-jump-buffer ... ))

(defun my-check-and-maybe-install (pkg)
  "Check and potentially install `PKG'."
  (when (not (package-installed-p pkg))
    (when (not (require pkg nil t))
      (package-install pkg))))

(defun my-packages-reset()
  "Reset package manifest to the defined set."
  (mapc 'my-check-and-maybe-install my-useful-packages))
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