cp: prevent error when source and destination are the same

Question

Can you tell cp (GNU coreutils) to prevent reporting an error on:

$ echo 1 > foo
$ cp foo foo

Currently, this reports:

cp: 'foo' and 'foo' are the same file

That's very sensible, but it's not always necessarily going to be an error. Conceptually, if you are copying files from $source to $dest, if you are already in the $dest directory, then essentially the copy is already done by construction; so, depending on context, this should not necessarily be reported as an error. I can't find anything in the manual page for this. The --update option doesn't work although it sounded like it might.

Obviously, I can work around this is many ways, but I was wondering if cp could do this off the bat.

Answer 1

This is not possible with GNU coreutils (as of coreutils 8.27). The documentation doesn't mention it, and the source code doesn't show any undocumented way. The test for same-file-ness only permits it when making hard links or in some cases where the files are symbolic links to the same destination.

Rsync allows it, so a simple solution would be to use rsync instead of cp.