How to delete the contents of a buffer by name

Question

For example in gdb mode, there is a buffer named *input/output of <program name>*, that I want to clear each time I press C-c l.

Answer 1

In general, if you don't know the exact name of the buffer, you need to call buffer-list to obtain the list of buffers and filter the result to only act on the desired buffer(s).

Untested code:

(defun erase-buffers-matching (regexp)
  "Erase the content of all buffers whose name matches REGEXP."
  (interactive "sErase buffers matching: ")
  (save-match-data
    (mapc (lambda (buffer)
            (cond
             ((not (string-match regexp (buffer-name buffer))))
             ((and (buffer-file-name buffer) (buffer-modified-p buffer))
              (message "Skipping buffer %s with unsaved data" (buffer-name buffer))
             (t
              (with-current-buffer buffer
                (erase-buffer)))))
          (buffer-list))))

For the specific case of the GDB program output buffer, GDB keeps track of it. It's the gdb-inferior-io buffer.

(defun erase-gdb-inferior-io-buffer ()
  (interactive)
  (with-current-buffer (gdb-get-buffer 'gdb-inferior-io)
    (erase-buffer)))
(global-set-key (kbd "C-c l") 'erase-gdb-inferior-io-buffer)

Answer 2

If this is something you want to do often, you could define a function for it in your .emacs file. Otherwise you could type it out in scratch, evaluate it and then assign it a key binding?

You could try:

(defun my/clear_buffer ()
  (interactive) 
  (let ((tmp (buffer-name)))
  (if (get-buffer "<buffer name>")              ;; check if buffer exists
      (progn (switch-to-buffer "<buffer name>") ;; switch to the buffer
         (erase-buffer)                         ;; erase it
         (switch-to-buffer tmp)))))             ;; switch back