waituntil.go

package main

import (
	"errors"
	"flag"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"time"
)

const format = time.Kitchen

var (
	cmd, atTime string
)

type status int

const (
	ok   status = 0
	fail status = 1
)

func main() {
	var s status
	defer os.Exit(int(s))
	flag.StringVar(&cmd, "cmd", "", "Command to run at date.")
	flag.StringVar(&atTime, "time", "", "Date or time to run at. Uses time.Parse (http://golang.org/pkg/time/#Parse). Expected format: \""+format+"\".")
	flag.Parse()
	for inf := range run() {
		var err error
		switch v := inf.(type) {
		case status:
			s = v

		case error:
			_, err = fmt.Fprintf(os.Stderr, "Error: %s\n", v.Error())

		case string:
			_, err = os.Stdout.Write([]byte(v + "\n"))
		}

		if err != nil {
			panic(fmt.Sprintf("Fatal error: %s\n", err.Error()))
		}
	}

}

func run() (chn <-chan interface{}) {
	c := make(chan interface{})
	chn = c
	go func() {
		defer close(c)
		if cmd == "" || atTime == "" {
			c <- errors.New("Command or time unspecified")
			c <- fail
			return
		}
		t, err := time.Parse(format, atTime)
		if err != nil {
			c <- err
			c <- fail
			return
		}
		n := time.Now()
		future := time.Date(n.Year(), n.Month(), n.Day(), t.Hour(), t.Minute(), t.Second(), t.Nanosecond(), t.Location())
		c <- fmt.Sprintf("I'll be back at %+q", future)
		time.Sleep(future.Sub(n))
		c <- fmt.Sprintf("I'm back, running %+q.", cmd)
		spl := strings.Split(cmd, " ")
		err = exec.Command(spl[0], spl[1:]...).Start()
		if err != nil {
			c <- err
			c <- fail
			return
		}
		return
	}()
	return
}