How to write a custom find-file function

Question

I want to write a set of functions that call specific files, not by a specific name, but the newest file (with a certain suffix) in the directory. So far I've got

(defun org_lisp_dir ()
  (interactive)
  (switch-to-buffer (find-file-noselect "~/org/babeltest/c.org"))

but that doesn't get me the latest .org file. To do this I believe I need to use something like (eshell/ls something), but I'm not sure how to use (eshell/ls) or integrate a complex eshell command into my code. The actual command would be something like ls -Art *.org | tail -n 1 which works just fine in eshell, BTW.

Answer 1

You can use shell-command-to-string to get a shell command's output. From C-h f shell-command-to-string:

shell-command-to-string is a compiled Lisp function in ‘simple.el’.

(shell-command-to-string COMMAND)

Execute shell command COMMAND and return its output as a string.

For example, on my machine, your shell command gives

(let ((default-directory "~/org/"))     ; Ending slash is necessary
  (shell-command-to-string "ls -Art *.org | tail -n 1"))
    ⇒ "todo.org
"

Note: I have changed directory by setting default-directory before running the shell command, mostly because ls(1) can't tell file's full path. And there is also a trailing newline, which is not part of filename and needs to be removed, you can remove that from elisp or from shell.

---

Here is a command named foo for opening newest .org file in ~/org/ directory (non-recursively).

(defun foo ()
  (interactive)
  (let ((default-directory "~/org/"))
    (find-file (shell-command-to-string "ls -Art *.org | tail -n 1 | tr -d '\n'"))))

tr(1) is used here to remove trailing newline.

Answer 2

Use directory-files to get the list of files in a directory.

Then loop over that list (e.g. dolist), examining the last-modified dates using function file-attributes to identify the most recently modified file(s). Or you can use function file-newer-than-file-p to filter the list.

Use find-file (not find-file-noselect) when you have identified the file(s) you want to edit (I'm assuming you want to edit them).

(However, I don't think that the original creation date is available, if that's the information you are after.)