Auto install emacs packages with MELPA

Question

I want to declare all packages that I want to use in emacs in a init.el file. I wonder if its possible to load the missing packages with e.g. MELPA when I startup e

Answer 1

I liked @steckerhalter's answer because it doesn't require any package installation. I'm building upon it here with the following improvements:

• looking at package-selected-packages variables so you don't have to specify the packages manually. This variable is populated by custom-set-variables when you install a package via the package manager.

• do the network check only if there are packages not installed.

  (let ((not-installed-packages 
         (seq-remove 'package-installed-p package-selected-packages)))
  
    (when (consp not-installed-packages)
  
      (setq my-onlinep nil)
      (unless
          (condition-case nil
              (delete-process
               (make-network-process
                :name "my-check-internet"
                :host "elpa.gnu.org"
                :service 80))
            (error t))
        (setq my-onlinep t))
  
      (when my-onlinep
        (package-refresh-contents)
        (dolist (p not-installed-packages)
          (package-install p)))
  
      (let ((still-not-installed-packages 
             (seq-remove 'package-installed-p package-selected-packages)))
        (if (consp still-not-installed-packages)
            (message "Still not installed: %s" still-not-installed-packages)
          (message "Successfully installed: %s" not-installed-packages)))
      ))