Create single .pot file across mult. directories w/ gettext

Using rgettext <input> -o app.pot, I'm able to create a .pot file from
any source files in a particular directory. I've thus far been unable to
consolidate, for example, views from multiple controllers in to one,
convenient .pot file. I could do it manually, but seems like too much
hassle for what I'm sure can be automated somehow. Anyone know how to
accomplish this?