Re: exclude option for cp

[James Youngman]

On 6/24/07, Francky Leyn <address@hidden> wrote:
> What I would like is that I would be able to exclude
> local wastebaskets with directory name .scratch and
> the files in it. I would also like to be able to exclude
> files with a name *~ from the copy.

cd /source-dir
find . -name '.scratch' -prune -o \! -name '*~' -print0 | cpio -pmd0   /dest-dir

> I know I can do this
> with find, but it would be much more convenient if cp
> would have an option to exclude files from copying.

The Unix way is generally to make a tool do its designed task well,
and have a separate tool for separate tasks.  If you need to open a
bottle of beer, it's probably better to use a bottle opener than
modify your shoes to also function as a bottle opener.

This adds to the power of Unix.  It would really suck for example if
it were impossible to do what you want because cp didn't support the
exclusion of files.   Being able to use several tools in combination
is often very useful because it allows you to do things that the
authors of the separate tools didn't envisage.

> Suppose this option would be triggered with -e or --exclude

I suspect that a single-letter option may never be added to cp again
(the last one was -t, in 2004, and the one before that was -H in
2000).  The risk of unexpected results is probably too high.  For
example, someone might use the -ß option thinking it does the same
thing as the -ß option on some other version of Unix and gets a nasty
surprise.

> I then would be able to specify the copy as:
> cp -rvf -e '*~' -e .scratch
>
> What about the idea?
>
> Is someone willing to implement this?

I think you're unlikely to get a volunteer.  Don't forget that every
new feature imposes a future burden of testing and maintenance effort.
  All the code in coreutils needs to be tested in preparation for
every release.   Every time a "horizontal" modification needs to be
made through the code or the code needs to be refactored, someone will
need to look at, search or check all the code.   Extra code means
extra effort and extra exposure to bugs.

So generally, new features need to be compelling enough to justify the
extra effort (or be useful but so trivial to implement that the extra
effort is negligible).

James.