Directory monitoring and program execution in Go

.gitignore

*.8
*.6
monitor

Makefile

include $(GOROOT)/src/Make.inc

TARG=monitor
GOFILES=\
	monitor.go\

include $(GOROOT)/src/Make.cmd

monitor.go

package main

import (
	"exec"
	"log"
	"os"
	"syscall"
	"strings"
	"time"
)

func main() {
	var verbose *bool = new(bool)
	*verbose = true

	if len(os.Args) < 3 {
		os.Stdout.Write([]uint8("Usage: ./monitor [-v] <dir> <cmd> <args>\n"))
		os.Exit(1)
	}

	dir := os.Args[1]
	cmd := os.Args[2]
	args := os.Args[3:]
	if *verbose {
		log.Println("Verbose output enabled")
		log.Println("dir:", dir)
		log.Println("cmd:", cmd)
		log.Println("args:", args)
	}

	fd, errno := syscall.InotifyInit()
	if errno != 0 {
		panic("inotify init")
	}
	if *verbose {
		log.Println("inotify fd", fd)
	}

	for {
		wd := watch(fd, dir)
		if *verbose {
			log.Println("Watch", wd, dir, "on inotify fd", fd)
		}

		detectEvent(fd)
		if *verbose {
			log.Println("Change detected")
		}

		stopWatching(fd, wd)
		if *verbose {
			log.Println("Stopped watching", wd)
		}

		log.Println("Running", cmd, "in", dir)
		run(dir, cmd, args)
		if *verbose {
			log.Println("Run completed")
		}
	}
}

func watch(fd int, dir string) int {
	wd, errno := syscall.InotifyAddWatch(fd, dir, syscall.IN_ATTRIB)
	if errno != 0 {
		panic("add watch")
	}
	return wd
}

func stopWatching(fd, wd int) {
	syscall.InotifyRmWatch(fd, uint32(wd))
	detectEvent(fd)
}

func detectEvent(fd int) {
	raw := make([]byte, 80)
	_, errno := syscall.Read(fd, raw)
	if errno != 0 {
		panic("read inotify")
	}
}

func run(dir, cmd string, args []string) {
	time.Sleep(50) // Avoid running before the modified file has been fully modified.
	c := exec.Command(cmd, strings.Join(args, " "))
	err := c.Run()
	if err != nil {
		//panic(err)
	}
}