;;; -*- lexical-binding: t -*-
;;
;; this file:
;;   https://dataswamp.org/~incal/emacs-init/switch-to-buffer-regexp.el

(require 'cl-lib)
(require 'buc)

(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

(keymap-global-set "C-c u" (lambda () (interactive) (switch-to-buffer-regexp "\*unsent posting\*.*")))
;; hit again to iterate

(provide 'switch-to-buffer-regexp)