A script to run before the ionic build process that generates an app.config.ts file based off of a .env/{environment}.json file. See this comment for more info: https://github.com/ionic-team/ionic-app-scripts/issues/762#issuecomment-295235407

Ionic environment

#!/usr/bin/env node
var path = require('path');
var process = require('process');
var fs = require('fs');

class Environment {
  constructor(args) {
    args = JSON.parse(args).original;
    const defaultEnv = 'development'; //Set default environment
    let env;
    
    if(args.includes('ionic:build')) {
      let envFlags = args.filter((arg) => arg.includes("--env"));
      env = (envFlags.length === 1) ? envFlags[0].substr(envFlags[0].indexOf("=") + 1) : defaultEnv;
    } else {
      let index = args.indexOf('--env');
      env = (index > -1) ? args[index+1] : defaultEnv;
    }

    console.log(`Using environment config: ${env}`);
    this.setEnvironment(env);
  }

  setEnvironment(env) {
    let config;
    
    try {
      config = require(path.join('../', '.env', env + '.json'));
    } catch(e) {
      throw new Error(`The config file for this environment is missing (${e.message})`);
    }

    var wstream = fs.createWriteStream(path.resolve('./src/app/app.config.ts'));
    wstream.write(`
      import { OpaqueToken } from "@angular/core"; //Use InjectionToken in Angular 4.x
      export let APP_CONFIG = new OpaqueToken("app.config");
      export const AppConfig = ${JSON.stringify(config)};
    `);
    wstream.end();
  }
}

new Environment(process.env.npm_config_argv);

@rossholdway any updates on this? Did you get this working again with the --env= flag?