.env

URL_API=http://www.minhaapi.com.br/meu-endpoint
TOKEN_NAME=access_token

angular_set_environtment.ts

const fs = require('fs');
const dotenv = require('dotenv');
dotenv.config();

const targetPath = `./src/environments/environment.ts`;
const envConfigFile = `
export const environment = {
  url_api: "${process.env.URL_API}",
  token_name: "${process.env.TOKEN_NAME}"
};
`
fs.writeFile(targetPath, envConfigFile, function (err) {
  if (err) {
    console.log(err);
  }
  console.log(`Output generated at ${targetPath}`);
});

//ts-node set-env.ts

package.json

{
    "scripts": {
        "ng": "ng",
        "config": "ts-node ./scripts/angular_set_environtment.ts",
        "start": "npm run config && ng serve",
        "build": "npm run config && ng build",
        "test": "ng test",
        "lint": "ng lint",
        "e2e": "ng e2e"
    }
}