Individual file level caching

Apologies if this is a particularly silly question and I am just overlooking something obvious here. However as a part of a static site build process I want to run several commands across all pages in my website (or ideally, only those that have changed). I have a step like this for example to generate the import maps based on what modules are imported on that page.

```json
"build-dev": {
"command": "node build/build-jspm-dev.js",
"clean": false,
"files": [
"www/**/*.html",
"build-jspm"
],
"output": [
"www/**/*.html"
],
"dependencies": [
"tsc",
"postcss"
]
},
```

Right now that script will just loop over all the relevant files and run the command. How could I instead change it to be more like
```bash
node build/build-jspm-dev.js file_that_changed.html
```