Question

there.

I always use the emacs editor. And I write some lisp(emacs-lisp) code.

But, I do not know that how to use the argument of file-name-sans-versions.

On manual,

=====

(file-name-sans-versions NAME &optional KEEP-BACKUP-VERSION)

Return file NAME sans backup versions or strings.
This is a separate procedure so your site-init or startup file can
redefine it.
If the optional argument KEEP-BACKUP-VERSION is non-nil,
we do not remove backup version numbers, only true file version numbers.

=====

I do not understand this sentences => we do not remove backup version numbers, only true file version numbers.

So, please teach me “how to” by sample code.

thanks.

Answer 1

There is an example in the elisp manual, in the (elisp) File Name Components node:

If KEEP-BACKUP-VERSION is non-`nil’, then true file version numbers understood as such by the file system are discarded from the return value, but backup version numbers are kept.

      (file-name-sans-versions "~rms/foo.~1~")
           => "~rms/foo"
      (file-name-sans-versions "~rms/foo~")
           => "~rms/foo"
      (file-name-sans-versions "~rms/foo")
           => "~rms/foo"

This doesn’t explain the difference between backup version numbers and true file version numbers. But the section I have bolded suggests that this is dependent on the particular file system in use. The same page includes the following:

For some purposes, the nondirectory part is further subdivided into
the name proper and the “version number”. On most systems, only backup
files have version numbers in their names.

I take this to mean that most operating systems don’t implement a true file version number as part of the file name.