Get your current IP in Emacs Lisp

get-current-ip.el

(defun get-ip (interface)
  (save-excursion
    (with-temp-buffer
      (call-process "/sbin/ifconfig" nil t nil "-a")
      (goto-char (point-min))
      (when (re-search-forward interface nil t)
        (case system-type 
          (gnu/linux (re-search-forward "inet addr:\\([^ ]*\\)"))
          (darwin (re-search-forward "inet \\([^ ]*\\)" nil t)))
        (buffer-substring (match-beginning 1)
                          (match-end 1)))
        )
      ))