Based on the following blog post: http://bradylove.com/blog/2013/05/24/commanding-tmux-with-emacs/

gistfile1.el

(defun tmux-display-message(arg)
  (s-trim-right (shell-command-to-string (format "tmux display-message -p '#%s'" arg))))

(defun tmux-get-current-session-name()  (tmux-display-message "S"))
(defun tmux-get-current-window-number() (tmux-display-message "I"))
(defun tmux-get-current-pane()          (tmux-display-message "P"))

(defun tmux-get-runner-pane()
  "Get # of current pane, and then use that to guess the # of the runner/term pane.

  I wonder if there is a better way to do this?" 
  (+ (string-to-number (tmux-get-current-pane)) 1))

;; http://ergoemacs.org/emacs/modernization_elisp_lib_problem.html
(defun s-trim-right (s)
  "Remove whitespace at the end of S."
  (if (string-match "[ \t\n\r]+\\'" s)
      (replace-match "" t t s)
    s))

(defun tmux-exec (command &optional pane-number)
  "Execute command in tmux current tmux session, window and pane."
  (interactive)
  (shell-command-to-string
    (format "tmux send-keys -t %s:%s.%s '%s' Enter" 
      (tmux-get-current-session-name) (tmux-get-current-window-number) 
      (if pane-number pane-number (tmux-get-current-pane)) command)))

(defun tmux-exec-in-runner-pane-or-without (command)
  "Tries to execute in runner pane; if output indicates no success, execute w/o tmux."
   (if (string-prefix-p "can't find pane:" (tmux-exec command (tmux-get-runner-pane)))
       (shell-command command)))

(defun tmux-exec-in-runner-pane-or-without-interactive(command)
  (interactive "sTmux/Shell Command: ")
  (tmux-exec-in-runner-pane-or-without command))