The #W3C html-xml-utils have been in development since 2004, and if you're building a static website on a #Unix system they're still useful.

#hxinclude will let you include HTML partials using syntax reminiscent of #Apache #ServerSideIncludes.

#hxtoc will let you generate a table of contents for a page.

#hxnormalize is a lightweight version of #tidy if all you want is pretty markup.

There's lots more, and you can pipe them in a script. (I should blog about this...)

https://www.w3.org/Tools/HTML-XML-utils/