How to define different environment and run it via Angular CLI?

I have two environments, one for staging and another for production. They both have different URLs and I want to build my project using Angular CLI. Right now I have to comment one URL and run another. But I want to control these things directly from the environment file.

I used this way (from Different proxy config based on environment in Angular 2 CLI):

// environment.ts
export const environment = {
    production: false,
    api: 'http://localhost:3000'
};

// environment.prod.ts
export const environment = {
    production: true,
    api: 'http://api.exampledomain.com'
}

Then in your ts source files pull the domain from the environment file:

// some service
import { Injectable } from '@angular/core';
import { environment } from '../../../environment.ts';
import { Http } from '@angular/http';

@Injectable()
export class SomeService {
    constructor(private http: Http);

    getData(){
        return this.http.get(environment.api + '/rest-of-api');
    }
}

But in this if I want to build from production how do I change environment variable value? Because here I import from environment.ts, not environment.prod.ts.