Question

More than once I’ve lost work by accidentally killing a temporary buffer in Emacs. Can I set up Emacs to give me a warning when I kill a buffer not associated with a file?

Answer 1

Make a function that will ask you whether you’re sure when the buffer has been edited and is not associated with a file. Then add that function to the list kill-buffer-query-functions.

Looking at the documentation for Buffer File Name you understand:

• a buffer is not visiting a file if and only if the variable buffer-file-name is nil

Use that insight to write the function:

(defun maybe-kill-buffer ()   (if (and (not buffer-file-name)            (buffer-modified-p))       ;; buffer is not visiting a file       (y-or-n-p 'This buffer is not visiting a file but has been edited.  Kill it anyway? ')     t)) 

And then add the function to the hook like so:

(add-to-list 'kill-buffer-query-functions 'maybe-kill-buffer)