Creates a keybinding that links to the most recently edited file of a directory.

insert-newest-link.el

(defun ms-filter-dirs (filelist)
  (remove-if (lambda (file) (file-directory-p file)) filelist))
(defun ms-newest-file (dir)
  (reduce (lambda (accum file)
            (if (file-newer-than-file-p file accum)
                file
              accum))
          (ms-filter-dirs (directory-files dir t))))
(defun ms-insert-newest-file (dir)
  (lexical-let ((dir dir))
    (lambda ()
      (interactive)
      (org-insert-link :link-location (concat "file:"
                                              (ms-newest-file dir))))))

(global-set-key (kbd "C-c C-S-l") (ms-insert-newest-file "~/Downloads"))

hi - I think this is exactly what I need! unfortunately executing results in 'Symbol's function definition is void: lexical-let"
With debugger 'on':
Debugger entered--Lisp error: (void-function lexical-let)

EDIT - just found out I needed to add (require 'cl)

Now there is another message after executing 'ms-insert-newest-file'
Symbol's function definition is void: org-insert-link

EDIT 2 -Apparently need a more recent org-mode version? Will install later and try again.

EDIT 3 - Installed the latest org version and indeed something is happening now, but it is still not working as expected. The error is gone though. If I am executing in a txt file something is created after being prompted with description: -> [[Downloads/tst]] it should be [[file:Downloads/tst.txt]] to work in org though.
Doing the same in an org file doesn't result in anything.
Org version 9.05 and Emacs 24.5.1

EDIT 4 - Now finally tried it on the target device that has a more recent Emacs version 25.1.1 and updated Org to 9.05
Directory where emacs should be looking is /media/mmc1/DCIM so I updated global-set-key to :
(global-set-key (kbd "C-c C-r") (ms-insert-newest-file "/media/mmc1/DCIM"))

Tried again and the same issue with a .org file. Nothing happens.
The .txt file shows [[../../media/mmc1/DCIM/20170411_01.jpg]]

That is already quite promising, but it should be [[file:/media/mmc1/DCIM/20170411_01.jpg]] and of course also working with an org file - the picture in the 'link' is indeed the latest picture added in the directory. Hope you can find the cause of the issue.

hi - I think this is exactly what I need! unfortunately executing results in 'Symbol's function definition is void: lexical-let"
With debugger 'on':
Debugger entered--Lisp error: (void-function lexical-let)
EDIT - just found out I needed to add (require 'cl)

Yeah, that's part of cl. All it's doing is allowing that dir parameter from ms-insert-newest-file to be used in the lambda function it's returning. You can see in the initial gist I used to just create the function in global-set-key. You can do that if you don't want to include cl.

I'm going to remove the relative filename conversion and append "file:" to the link, that should put the generated link in the correct format.