Ideally, you shouldn't need the hathifiles.
The HathiTrust search page links to an OpenSearch document , which promisingly identifies an RSS feed and a JSON serialization of the search results. Neither appears to work. In theory, doing as Jon says and then appending "&view=rss" would get you an RSS feed. There is a contact email in the OpenSearch document you might try.
FWIW, if you look at the search page HTML, there is a "fixme" note in an HTML comment, the same comment, incidentally, that also comments out the RSS feed link in the HTML.
> -----Original Message-----
> From: Code for Libraries [mailto:[log in to unmask]] On Behalf Of
> Jon Stroop
> Sent: Friday, August 03, 2012 11:15 AM
> To: [log in to unmask]
> Subject: Re: [CODE4LIB] haititrust
> You can do an empty query in their catalog, and use the "Original
> Location" facet to filter to a holding library. Programatically, I'm
> not sure, but you'd probably need to use the Hathi files:
> On 08/03/2012 11:07 AM, Eric Lease Morgan wrote:
> > If I needed/wanted to know what materials held by my library were
> > in the HaitTrust, then programmatically how could I figure this out?
> > In other words, do you know of a way to query the HaitTrust and limit
> > the results to items my library owns? --Eric Lease Morgan