Unattended install of a set of packages

Question

Given a requirements.txt file describing a Python virtual environment, one can run pip install requirements.txt, go for a coffee, then come back to find that the packages in requirements.txt have been installed.

Is there a mechanism in Emacs (25.x, 26.x) to install a list of packages without attending to the installation by running a sequence of M-x package-install?

Answer 1

One can use use-package. In a file (which could be your init file, but doesn't have to be):

(require 'package)
(add-to-list 'package-archives
             '("melpa" . "https://melpa.org/packages/") t)
(package-initialize)

(setq package-archives
      (seq-remove (lambda (element)
                    (equal "gnu" (car element)))
                  package-archives))
(add-to-list 'package-archives
             '("gnu" . "https://elpa.gnu.org/packages/"))

;; bootstrap use-package, so I can use it to manage everything else
(unless (package-installed-p 'use-package)
  (package-refresh-contents)
  (package-install 'use-package))

(eval-when-compile (require 'use-package))

(use-package use-package
  :config
  (setq use-package-always-ensure t))

Then you can set up all your packages as follows:

(use-package package1)
(use-package package2)

When this file is evaluated (which, if it's your init file, is on startup), Emacs will install all the packages you've set up this way. If a package is already installed, use-package will skip the installation; it won't be updated to the latest. You can use other features of use-package to configure each installed package.