Using environments in Ionic

app.module.ts

import { EnvironmentsModule } from '../environment/environment.module';

@NgModule({
  ...
  imports: [
  ...
  EnvironmentsModule,
  ...
  ]
  ...
}

env.develop.ts

import { IEnvironmentalVariables } from './env.variables';

export const devConfig: IEnvironmentalVariables = {
  apiUrl: 'https://...',
  googleOAuth: '6047....apps.googleusercontent.com',
  kmsApiKey: '7a...1e',
  logToConsole: true
};

env.production.ts

import { IEnvironmentalVariables } from './env.variables';

export const productionConfig: IEnvironmentalVariables = {
  apiUrl: 'https://...',
  googleOAuth: '6047....apps.googleusercontent.com',
  kmsApiKey: '7a...1e',
  logToConsole: true
};

env.uat.ts

import { IEnvironmentalVariables } from './env.variables';

export const uatConfig: IEnvironmentalVariables = {
  apiUrl: 'https://...',
  googleOAuth: '6047....apps.googleusercontent.com',
  kmsApiKey: '7a...1e',
  logToConsole: true
};

env.variables.ts

export interface IEnvironmentalVariables {
  apiUrl: string;
  googleOAuth: string;
  kmsApiKey: string;
  logToConsole: boolean;
}

environment.module.ts

import { NgModule } from '@angular/core';
import { Environment } from './environment.token';
import { uatConfig } from './env.uat';
import { productionConfig } from './env.production';
import { developConfig } from './env.develop';

export function environmentFactory() {
  switch (process.env.NODE_ENV) {
    case 'uat':
      return uatConfig;
    case 'dev':
      return developConfig;
    case 'prod':
      return productionConfig;
    default:
      throw new Error('Enviroment not set');
  }
}

@NgModule({
  providers: [
    {
      provide: Environment,
      useFactory: environmentFactory
    }
  ]
})
export class EnvironmentsModule { }

environment.token.ts

import { OpaqueToken } from '@angular/core';

// tslint:disable-next-line:variable-name
export const Environment = new OpaqueToken('environment');

file needing access to config.ts

class MyClass {
  constructor(@Inject(Environment) private _env: IEnvironmentalVariables){
  }
}

To set the enviroment you then need to run ionic commands having set NODE_ENV like:
NODE_ENV=uat bash -c 'ionic cordova build android --prod --release'