[stevekemp]

I wrote something that works like that, called templer:

https://github.com/skx/templer

In the past I wrote all my HTML pages by hand. Then I started just writing the "body"-area, and concatenating a header, footer, and the body together to generate output. After that I started to make more changes.

In the end it grew, as these things do, but at the core templer allows you to put "stuff" into a "layout", and generates the output. It might suit you, or it might not. But there are many similar tools out there.