Question

I have a function that launches programs asynchronously:

(defun app (app-name)
  (interactive "sRun application: ")
  (async-shell-command app-name))

And i have a list of all executables from which to choose. I want the app function to behave as switch-to-buffer, providing TAB-completion for user. How do i use minibuffer completion in Emacs?

Answer 1

Use completing-read command. The function will look like

(defun app ()
  (interactive)
  (let ((app-name (completing-read "Run application: " program-list)))
    (async-shell-command app-name)))

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Possibly more idiomatic is to use interactive instead of assigning to a variable according to Emacs Lisp Idioms: Prompting for User Input:

(defun app (app-name)
  (interactive (list (completing-read "Run application: " app-list)))
  (async-shell-command app-name))

Also you can use (start-process app-name nil app-name) instead of (async-shell-command app-name), if you don’t care for process output according to Run a program from Emacs and don't wait for output.

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See Minibuffer Completion for more ideas on completion in Emacs and Asynchronous Processes for calling processes from Emacs, both from GNU manuals.