cross platform launcher program

launcher.go

package main

import (
	"fmt"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"time"
)

func help() {
	fmt.Println(`Thistle Launcher - allows to execute an update program before your main applcation
syntax: ./launcher [main_application args] [update_command args](defaults "./tuc") [seconds delay between update checks](defaults 7200)

e.g. ./launcher "/opt/myapp /etc/app_cfg"
e.g. ./launcher "/opt/myapp /etc/app_cfg" "/opt/thistle/tuc -c /etc/thistle.conf" 3600`)

	os.Exit(0)
}

func check_update(updaterBin string, updaterArgs []string) {
	fmt.Println("executing", updaterBin, "args:", updaterArgs)
	updaterCmd := exec.Command(updaterBin, updaterArgs...)
	updaterCmd.Stdout = os.Stdout
	updaterCmd.Stderr = os.Stderr
	updaterCmd.Start()
	updaterCmd.Wait()
}

func main() {
	args := os.Args[1:]

	if len(args) < 1 || (len(args) == 1 && (args[0] == "--help" || args[0] == "-h" || args[0] == "help")) {
		help()
	}

	program := strings.Fields(args[0])
	programBin := program[0]
	programArgs := program[1:]

	updaterDefault := "./tuc"
	var updater []string
	if len(args) >= 2 {
		updater = strings.Fields(args[1])
	} else {
		updater = strings.Fields(updaterDefault)
	}
	updaterBin := updater[0]
	updaterArgs := updater[1:]

	delay := 7200 * time.Second
	if len(args) >= 3 {
		seconds_parsed, err := strconv.Atoi(args[2])
		if err != nil {
			fmt.Println("Error parsing delay:", err)
			os.Exit(1)
		}
		delay = time.Duration(seconds_parsed) * time.Second
	}

	// check now
	check_update(updaterBin, updaterArgs)

	// and check every XXX seconds
	go func() {
		for {
			time.Sleep(delay)
			check_update(updaterBin, updaterArgs)
		}
	}()

	// main program
	fmt.Println("executing", programBin, "args:", programArgs)
	programCmd := exec.Command(programBin, programArgs...)
	programCmd.Stdout = os.Stdout
	programCmd.Stderr = os.Stderr
	programCmd.Start()
	programCmd.Wait()

}