Is it re-publishing?
N.B. I am most decidedly NOT a lawyer.
I'm happy to comply with sensible copyright and republishing protected material is wrong. I want my material protected so I need to be prepared to respect the property of others.
OK, it's not about the actual link. It could be a nice descriptive link, a redirection link, a self-evidently broken link that's easy to fix, or even search expression text. The point is that the distribution of the "link" is making it available a different "public". I read this as making it available to a new audience. We might better describe making it available to a new audience as re-publishing.
If I post material on a public facing web site, under my control, I consider that publishing publicly. The technicalities of the web require that each visitor copies the material to their own clients systems to view the material. That would seem to have an implied acceptance by the author. However, if the visitor makes the files available on a different site that would seem to be re-publishing the material and I (as the author) might, reasonably, consider this a violation.
Now, what if I put files on a public facing web site and share a link privately with friends? This doesn't change the fact that it's available to anyone who stumbles upon it. If the link becomes known to others and is shared, that would reach a new audience (i.e. no longer just my friends). Of course, at any time I can add some authorisation method that restricts access. That is, the material is still under my control and I'm not guaranteeing that the link will reach the material at any given time.
So, for me sharing the link is fine because the material is still under the control of the author. However, sharing the material (i.e. re-publishing) is a violation.
Just my 2p.