以前从网站上拉下来一个，不过使用了post-command-hook，参考修改了一下，能够比较及时显示。
;;;Emacs title bar to reflect file name
(defun frame-title-string ()
"Return the file name of current buffer, using ~ if under home directory"
(let
((fname (or
(buffer-file-name (current-buffer))
(buffer-name))))
;;let body
(when (string-match (getenv "HOME") fname)
(setq fname (replace-match "~" t t fname)) )
fname))
;;; Title = 'system-name File: foo.bar'
(setq frame-title-format '("" system-name " File: "(:eval (frame-title-string))))
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