[coreutils] basename/dirname can't handle stdin?

[Jeff Blaine]

I was surprised to find this today.

The following fails:

    echo /some/place/foo.txt | basename

This also fails:

    find /somewhere -print | xargs basename

This *does* work though, somehow, when the above does not:

    echo /some/place/foo.txt | xargs basename

What is going on here?  dirname is the same way.