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Marcin ‘mbork’ Borkowski

2024-02-17 Opening external drives in Dired

I use external drives pretty often – for backups, for moving files between machines, and for storing mp4 files, for example. I’ve been using UDisks for quite some time now. It automounts an external drive under the /run/media/$USER/VolumeName directory (where VolumeName is different for each drive, of course).

I also use Dired as my main file manager. As most Emacsers know, it’s far from shiny, but it’s incredibly powerful, especially combined with some other Emacs features.

One problem I have is that when I insert a drive into one of the USB ports, I’d like to be able to open it in Dired. I could of course create a bookmark pointing to it, but I don’t want to maintain a seperate bookmark for every drive I use. I could also bookmark the /run/media/mbork directory, but then I’d have to press one more key to get to the VolumeName directory. I figured that I could create a function which opens Dired in the root directory of my drive, assuming that it’s the only mounted one. (If there are more mounted drives – which means more directories under /run/media/mbork – the function should allow me to select one of them.) Of course, I could probably go even further, detect that a drive was mounted and open its directory in Dired automatically, but that might be a bit too much. Sometimes I don’t want to do anything with the drive (for example, when I use it only to make my daily backups), and sometimes I might be doing something else (for example reading or writing), and Emacs suddenly switching to another buffer would not be helpful.

Anyway, here’s some Lisp code I wrote in about 10 minutes.

(defcustom automount-directory (format "/run/media/%s" user-login-name)
  "Directory under which drives are automounted.")

(defun automount-open-in-dired ()
  "Open the automounted drive in Dired.
If there is more than one, let the user choose."
  (interactive)
  (let ((dirs (directory-files automount-directory nil "^[^.]")))
    (dired (file-name-concat
            automount-directory 
            (cond ((null dirs)
                   (error "No drives mounted at the moment"))
                  ((= (length dirs) 1)
                   (car dirs))
                  (t
                   (completing-read "Open in dired: " dirs nil t)))))))

And of course, if you want to learn to code your own convenience commands like this, as usual I recommend Introduction to programming in Emacs Lisp by the late Robert J. Chassell as an appetizer, and my book, Hacking your way around in Emacs, as the next course.

CategoryEnglish, CategoryBlog, CategoryEmacs

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