I've found lots of info online about appending date to filename before the extension, but none that do so only if there's an extension.
& if there's no extension, it goes at the end of file name.

This is how far I got.

for FILE in *; do
EXT=${FILE#*.};
NAME=${FILE%%.*};
mv "$FILE" "$NAME$(date --reference "$FILE" '+%d%m%y').$EXT";
done

that works provided there's an extension and the only . in filename is right before the extension.

It doesn't work if there's no extension or if there's another . in the filename.

Ideas for making this work for filenames with or without an extension ..
& with or wtihout a . elsewhere in filename?

thanks much;

see man test, and check -n or -z for example (that is for existing EXT).
see man bash, look for parameter expansion, especially ## (for several .)

Having no extension is a no brainer, but you will need someway to identify what you are considering a valid extension? If there is a period in the file name and no extension, I see no real way
of not placing the date inside the file name unless you have an acceptable list of extensions.

A long time ago I used to worry about things like this. Then I just decided the date would go on the end regardless - and told people to live with it.
Extensions have no intrinsic value in Linux.

2 members found this post helpful.

pan64, grail, syg00,

Thanks to all who replied. This is my third attempt to reply .. other two were eaten by glitches <grr> ..

I will try the suggestions.

I especially like syg00's suggestion, "deal with it approach" when the date is appended to the extension. This is especially time-efficient, unless (like me) you don't know which OS you'll be using in a month, functioning as I do with highly improvised hardware configurations.

grail's
> "If there is a period in the file name and no extension, I see no real way
> of not placing the date inside the file name unless you have an acceptable list of extensions."
.. is spot-on, if I can think of a complete list ..

pag64
> see man test, and check -n or -z for example (that is for existing EXT).
> see man bash, look for parameter expansion, especially ## (for several .)
Good idea.

EVL

Not a real solution but something that my work group has used for many years which works for us and is difficult to convey to others of the advantages is putting the date first as YYYYMMDD. Because of how alphanumeric sorting works using YYYYMMDD_file-name.ext makes sorting by name "automatic"

Doeshave an extension?
It's valid in thatcreates a file called a.a.txt.gzip. (according to ls).
However, fails to remove it.

will remove the file