Import code.google.com/p/go.exp/fsnotify (GoDoc) for the latest API under development.
Continue importing github.com/howeyc/fsnotify (GoDoc) for the stable API.
Report Issues to go.exp/fsnotify after testing against code.google.com/p/go.exp/fsnotify
Join golang-dev to discuss fsnotify.
See the Contribution Guidelines for Go and sign the CLA.

Example:

package main

import (
	"log"

	"github.com/howeyc/fsnotify"
)

func main() {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		log.Fatal(err)
	}

	done := make(chan bool)

	// Process events
	go func() {
		for {
			select {
			case ev := <-watcher.Event:
				log.Println("event:", ev)
			case err := <-watcher.Error:
				log.Println("error:", err)
			}
		}
	}()

	err = watcher.Watch("testDir")
	if err != nil {
		log.Fatal(err)
	}

	<-done

	/* ... do stuff ... */
	watcher.Close()
}

For each event:

Name
IsCreate()
IsDelete()
IsModify()
IsRename()

FAQ

When a file is moved to another directory is it still being watched?

No (it shouldn't be, unless you are watching where it was moved to).

When I watch a directory, are all subdirectories watched as well?

No, you must add watches for any directory you want to watch (a recursive watcher is in the works #56).

Do I have to watch the Error and Event channels in a separate goroutine?

As of now, yes. Looking into making this single-thread friendly (see #7)

Why am I receiving multiple events for the same file on OS X?

Spotlight indexing on OS X can result in multiple events (see #62). A temporary workaround is to add your folder(s) to the Spotlight Privacy settings until we have a native FSEvents implementation (see #54).

How many files can be watched at once?

There are OS-specific limits as to how many watches can be created:

Linux: /proc/sys/fs/inotify/max_user_watches contains the limit, reaching this limit results in a "no space left on device" error.
BSD / OSX: sysctl variables "kern.maxfiles" and "kern.maxfilesperproc", reaching these limits results in a "too many open files" error.

# Functions

NewWatcher

NewWatcher creates and returns a new inotify instance using inotify_init(2).