It depends on exactly what you're trying to do in the scripts, but it's likely that you can use **npm cli packages** to effectively add cross-platform commands to any shell.

For example, if you wanted to *delete a directory*, you could use separate syntaxes for windows and linux:

```bash
rm -rf _site     # bash
rd /s /q _site   # cmd
```

Or instead, you could use the npm package [**`rimraf`**][1] which works cross platform:

```
npx rimraf _site
```

To take Dave P's example above, you could set environment variables with [**`cross-env`**][3] like this:

```json
"scripts": {
    "test": "npx cross-env NODE_ENV=test mocha",
}
```

And if you don't want to use [**`npx`**][4] to install scripts live, you can install them globally ahead of time like this:

```bash
npm i cross-env -g
```



Here's a post I wrote on [making NPM scripts work cross platform][2] which explores some of these options

[1]: https://github.com/isaacs/rimraf#cli
[2]: https://docgov.dev/posts/npm-scripts/
[3]: https://www.npmjs.com/package/cross-env
[4]: https://medium.com/@maybekatz/introducing-npx-an-npm-package-runner-55f7d4bd282b

I would like to create a `package.json` build script that executes slightly different set of commands when run from Windows, Linux, Mac.

The problem is that I cannot find a way to put it in `package.json` file that will run without problems at every system.

Here is an example that I would like to have:

    "scripts" : {
        "build.windows" : "echo do windows specific stuff",
        "build.linux" : "echo do linux specific stuff",
        "build.mac" : "echo do mac specific stuff",
        "build" : "??????????????" <- what to put here to execute script designed for OS
                                      on which npm is running
    }