The pipeline approach here is interesting, but it seems you'd be on your own for filtering out changes in the build directory, etc. I typically use watchexec [1] for this.

    watchexec make

By default, watchexec will filter out changes in files based on `.gitignore`.

[1]: https://github.com/watchexec/watchexec

This is pretty good, didn't know about watchexec, but you can achieve the same by choosing carefully the command you pipe from, for example:

    ls *.md | make

Will only trigger the build if a md file is modified, which is what I think the author is interested in.

I personally use fswatch for this. The invocation is probably something like this:

    fswatch -0 ***.md | xargs -0 make

I invoke a variant of this from my Makefile with a phony watch target. I think the main change is that I also echo a bell character, to provide some feedback.

Fun tip: Preview will automatically reload PDFs on disk, though with some limitations that I workaround by waiting for the bell.