;;; -*- lexical-binding: t -*-
;;;
;;; this file:
;;;   http://user.it.uu.se/~embe8573/emacs-init/switch-to-buffer-regexp.el
;;;   https://dataswamp.org/~incal/emacs-init/switch-to-buffer-regexp.el

(require 'cl-lib)

(defun buffer-names ()
  (mapcar #'buffer-name (buffer-list)) )

(defun switch-to-buffer-regexp (buf-re)
  (let*((ori-buf  (buffer-name (current-buffer)))
        (hits     (cl-remove-if-not
                   (lambda (b) (string-match buf-re b)) (buffer-names)) ))
    (when hits
      (let ((new-hits (cl-remove ori-buf hits)))
        (when new-hits
          (when (string-match buf-re ori-buf)
            (bury-buffer ori-buf) )
          (switch-to-buffer (car new-hits)) )))))

;; try it!
;; (require 'gnus)
;; (dotimes (i 4) (gnus-post-news 'post "")) ; create 4 posts

(global-set-key "\C-cu" (lambda () (interactive) (switch-to-buffer-regexp "\*unsent posting\*.*")))
(global-set-key "\C-ck" (lambda () (interactive) (switch-to-buffer-regexp ".*\.txt")))
;; hit again to iterate

(provide 'switch-to-buffer-regexp)