Should not overwrite already defined variables

The [dotenv](https://www.npmjs.com/package/dotenv) module does not overwrite already defined environment variables. Should this module not behave the same?
This could be done by using the [dotenv](https://www.npmjs.com/package/dotenv)

```js
const dotenv = require('dotenv')
const names = Object.keys(dotenv.load().parsed);

console.log(names.map((name) => { return `export ${name}=${process.env[name]};`}).join("\n"));
```