The function to show current file's full path in mini buffer

I need to get the full path of the file that I'm editing with emacs.

Is there a function for that?
If not, what would be the elisp function for getting that?
How can I copy the result (path name) to a clipboard so that I can reuse it?

I'm using Mac OS X and Aqumacs.

(setq filepath (get-fullpath-current-file)) ???
(copy-to-clipboard 'filepath) ???

ADDED

(defun show-file-name ()
  "Show the full path file name in the minibuffer."
  (interactive)
  (message (buffer-file-name))
  (kill-new (file-truename buffer-file-name))
)
(global-set-key "\C-cz" 'show-file-name)

Combining the two answers that I got, I could get what I want. Thanks for the answers. And some more questions.

What's for (file-truename)?
Can I copy the path name to System(OS)'s clipboard, not the kill ring so that I can use the info with the other apps?

Solution

It's the built-in function buffer-file-name that gives you the full path of your file.

The best thing to do is to have your emacs window to always show your system-name and the full path of the buffer you're currently editing :

(setq frame-title-format
      (list (format "%s %%S: %%j " (system-name))
        '(buffer-file-name "%f" (dired-directory dired-directory "%b"))))

You can also do something like this :

(defun show-file-name ()
  "Show the full path file name in the minibuffer."
  (interactive)
  (message (buffer-file-name)))

(global-set-key [C-f1] 'show-file-name) ; Or any other key you want