Thanks, Lei, your code works. And I has extended it to a lisp codesnnipet,
which is exactly what I want.

I post it here, in case others need it.

Notice: There is an enhancement here, which is replacing setq with local
variables.
I tried to do this, but has failed, due to my poor lisp.
Since this is a minor issue for me, so I keep lazy here. ^-^

;; -------------------------- separator --------------------------
(setq frame-title-format
      '(:eval (concat "Ask 5 why, Denny! -- " (buffer-name) " -- "
                      (progn
                        (if buffer-file-name
                            (setq buffer_name_str buffer-file-name)
                          (setq buffer_name_str ""))
                        (if (< (length buffer_name_str) 50)
                            buffer_name_str
                          (concat (substring buffer_name_str 0 20) "..."
                                  (substring buffer_name_str
                                             (- (length buffer_name_str) 30)
                                             (length buffer_name_str))
                           ))))))

;; -------------------------- separator --------------------------

Regards,
Denny


On Sat, Jul 31, 2010 at 3:30 PM, Wang Lei <f3d27b@gmail.com> wrote:

> On 7/31/10, filebat Mark <filebat.mark@gmail.com> wrote:
> > Hi Lennart
> >
> > I tried  (setq frame-title-format "%f - Emacs"), it's cool.
> >
> > However, the full filename of "%f" is usually too long.
> > Can I truncate the string with fixed length?
> >
> > Regards,
> > Denny
> You can try this.
> (setq frame-title-format '(:eval (concat (if (< 10 (length
> buffer-file-name))
>                                             (concat (substring
> buffer-file-name 0 6) "...")
>                                           buffer-file-name)
>                                         "- Emacs")))
>
> I assume 10 is the max length of filename than you want to.
>
>
> >
> > On 7/28/10, Lennart Borgman <lennart.borgman@gmail.com> wrote:
> >>
> >> On Wed, Jul 28, 2010 at 3:14 PM, Kevin Rodgers
> >> <kevin.d.rodgers@gmail.com> wrote:
> >> >
> >> > Tim Visher wrote:
> >> >>
> >> >> Hi everyone,
> >> >>
> >> >> I'm wondering if there's a simple way to postfix ' emacs' to all
> frame
> >> >> titles without resorting to [elisp from the web][1].  Couldn't find
> >> >> anything in Chapter 25 but I didn't search much harder than that.
> >> >>
> >> >> [1]: http://www.emacswiki.org/emacs/FrameTitle
> >> >
> >> > No, you need to use Emacs Lisp: that is the "format" of customizations
> >> > in ~/.emacs (M-x customize notwithstanding).
> >> >
> >> > Here's what I use:
> >> >
> >> > (setq frame-title-format
> >> >      '("" invocation-name "-" emacs-version "@" system-name ":"
> >> >        (buffer-file-name "%f" "%b")))
> >>
> >>
> >>
> >> In EmacsW32 I use
> >>
> >>   (setq frame-title-format "%b - Emacs")
> >>
> >> This is probably what people on ms windows expect. Is that what people
> >> on other GUI systems expect as well?
> >>
> >>
> >
> >
> > --
> > Thanks & Regards
> >
> > Denny Zhang
> >
>
>
> --
> Regards,
> Lei
>



-- 
Thanks & Regards

Denny Zhang