watch-and-move.go

package main

import (
	"fmt"
	"github.com/fsnotify/fsnotify"
	"os"
	"path/filepath"
	"sync"
)

func main() {
	watchDir := "watch-dir"
	moveToDir := "move-to-dir"

	ce := func(err error) {
		if err != nil {
			panic(err)
		}
	}

	l := new(sync.Mutex)
	moveFiles := func() {
		l.Lock()
		defer l.Unlock()
		dir, err := os.Open(watchDir)
		ce(err)
		names, err := dir.Readdirnames(-1)
		ce(err)
		wg := new(sync.WaitGroup)
		wg.Add(len(names))
		sem := make(chan struct{}, 8)
		for _, name := range names {
			sem <- struct{}{}
			name := name
			go func() {
				defer func() {
					wg.Done()
					<-sem
				}()
				from := filepath.Join(watchDir, name)
				to := filepath.Join(moveToDir, name)
				fmt.Printf("move %s to %s\n", from, to)
				ce(os.Rename(from, to))
			}()
		}
		wg.Wait()
	}

	watcher, err := fsnotify.NewWatcher()
	ce(err)
	defer watcher.Close()
	ce(watcher.Add(watchDir))

	go func() {
		for {
			select {
			case event := <-watcher.Events:
				if event.Op&fsnotify.Create == 0 {
					continue
				}
				moveFiles()
			case err := <-watcher.Errors:
				ce(err)
			}
		}
	}()

	moveFiles()

	select {}
}