This is a demo code to export multiple HTML files or a single PDF file from the same multiple Org files. Org Mode, as of version 9.1.x, does not have a capability to export to multiple files, ie. each chapter on each HTML file.
This demo is trying to mimic the capability by using Macro replacement.
Just type make should work if your Emacs is setup to use Org Mode,
HTML and latex exporters.
If you have a version of Emacs in somewhere else, just define EMACS.
$ make EMACS=~/src/emacs26/src/emacs
This demo is tested with GNU Emacs 25.2.2 and GNU Emacs 26.0.91.