new-shell.el

(require 'cl)

(defun new-shell ()
  "Create new shells with consecutive names *shell-1*, *shell-2*, etc.                                                                                                                         
  Remove any stale shells (shells without a live process)"
  (interactive)
  (let* ((regex "^\\*shell-\\([0-9]+\\)\\*$")
         (shell-buffers (loop for buffer in (buffer-list)
                             if (string-match regex (buffer-name buffer))
                             collect buffer))
         (max-buffer-num) (active-shell-buffers) (new-num))
    (loop for buffer in shell-buffers
          if (not (get-buffer-process buffer))
          do (kill-buffer buffer))
    (setq active-shell-buffers (loop for buffer in shell-buffers
                                     if (buffer-live-p buffer)
                                     collect buffer))
    (setq max-buffer-num (loop for buffer in active-shell-buffers
                               for buffer-name = (buffer-name buffer)
                               for buffer-num-s = (progn
                                                    (string-match regex buffer-name)
                                                    (match-string 1 buffer-name))
                               for buffer-num = (string-to-number buffer-num-s)
                               maximize buffer-num))
    (setq new-num (1+ (or max-buffer-num 0)))
    (shell)
    (rename-buffer (format "*shell-%d*" new-num))))