spawn.ts

import * as Rx from "rxjs";
import * as CP from "child_process";

function spawn(cmd: string, args: string[] = []): Rx.Observable<ProcessOutput>  {
  return Rx.Observable.create(observer => {
    let process = CP.spawn(cmd, args);
    process.addListener("error", err => {
      observer.error(err);
    });
    process.addListener("exit", code => {
      observer.next({ kind: "exit", code });
      observer.complete();
    });
    process.stderr.addListener("data", data => observer.next({ kind: "stderr", data }));
    process.stdout.addListener("data", data => observer.next({ kind: "stdout", data }));
    return new Rx.Subscriber(() => {
      process.kill();
    });
  });
}

type ProcessOutput 
= {
    kind: "exit",
    code: number
  }
| {
  kind: "stderr",
  data: any
}
| {
  kind: "stdout",
  data: any
}
;