Getting the directory of the active buffer

Sometimes it's useful to get the current directory of the buffer that you are currently editing. For me, it's usually when I edit a file, and I want to go to that directory in a shell buffer. I solve this problem using the following function:

(defun em-copy-path-of-buffer ()
  (interactive)
  (kill-new default-directory)
  (message "Copied '%s'" default-directory))

By calling this function (either by using M-x em-copy-path-to-buffer or by binding it to a key) the path is copied to the kill ring, and I can paste it using C-y into the shell buffer.