Sorry not to even try myself. It's been years. I don't mind which
flavour of shell. Thanks.

    for f in *.*
    do
        ext=$( tr "a-zA-Z" "n-za-mN-ZA-M" <<< "${f##*.}" )
        mv -i "$f" "${f%.*}.${ext}"
    done

Janis

Here are some notes to myself:

(01)(06)(09).mp3   09 06 01
army style: dayNum=1 monthNum=2 YrNum=3
sortable:   YrNum=3 monthNum=2 dayNum=1

(dired-do-rename-regexp "\\(globalresearch\\)\\([0-9][0-9]\\)\\([0-9][0-9]\\)\\([0-9][0-9]\\).mp3" "GR-\\3\\2\\4.mp3")
(dired-do-rename-regexp "\\(GR-\\)\\([0-9][0-9]\\)\\([0-9][0-9]\\)\\([0-9][0-9]\\).mp3" "\\1\\4\\3\\2.mp3")

I use the above to change the name of .mp3-files from a particular
place (globalResearch.ca -- HAVE A LOOK!) to change the format
and order of date parts so that they'll sort, ie be listed in
the order I want, thata is, by date (I rearrange the date and
move it to the left side of the file-name).

where that function is described (by emacs) as:

 |  % R runs the command dired-do-rename-regexp
 |    which is an interactive compiled Lisp function in `dired-aux.el'.
 |  It is bound to % r, % R, <menu-bar> <regexp> <rename>.
 |  (dired-do-rename-regexp regexp newname &optional arg whole-name)
 |
 |  Rename selected files whose names match regexp to newname.
 |
 |  With non-zero prefix argument arg, the command operates on the next arg
 |  files.  Otherwise, it operates on all the marked files, or the current
 |  file if none are marked.
 |
 |  As each match is found, the user must type a character saying
 |    what to do with it.  For directions, type C-h at that time.
 |  newname may contain \<n> or \& as in `query-replace-regexp'.
 |  regexp defaults to the last regexp used.
 |
 |  With a zero prefix arg, renaming by regexp affects the absolute file name.
 |  Normally, only the non-directory part of the file name is used and changed.

Another emacs example is this function (via dired-x.el, I think):

*** WDIRED:  M-x wdired-change-to-wdired-mode --> mode-line: "[(Editable Dired)]"   dired-edit
            rename files via simply **EDITING** the names IN THE DIRED BUF ITSELF!
  Command: Toggle Dired-Omit mode.

Hope this helps SOMEONE!

David