interprogram-cut/paste-functions

[bkhl@elektrubadur.se (Björn Lindström)]

I'm trying to get my text mode Emacs session to interoperate with my X
clipboard, using xsel (http://www.vergenet.net/~conrad/software/xsel/).

The following sort of works, except that when I yank something in Emacs,
the empty string gets pushed to kill-ring. I suspect that I
misunderstand when interprogram-paste-function is supposed to return
nil, but I need help figuring out how.

Here's my attempt so far:

(defun bkhl-cut-function (text &optional push)
    (with-temp-buffer
      (insert text)
      (call-process-region (point-min) (point-max) "xsel" nil 0 "--input")))
(setq interprogram-cut-function 'bkhl-cut-function)

(defun bkhl-paste-function ()
  (let ((text (with-output-to-string
		(with-current-buffer standard-output
		  (call-process "xsel" nil standard-output nil "--output")))))
    (unless (string= (car kill-ring) text)
      text)))
(setq interprogram-paste-function 'bkhl-paste-function)