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radovskyb/watcher: watcher is a Go package for watching for files or directory changes without using filesystem events.

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Original source (github.com)
Tags: filesystem golang go fs-notify watcher
Clipped on: 2020-03-10

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watcher is a Go package for watching for files or directory changes without using filesystem events.
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README.md

watcher

Image (Asset 4/4) alt= Features
Example
Contributing
Watcher Command

Update

  • Event.OldPath has been added [Aug 17, 2019]
  • Added new file filter hooks (Including a built in regexp filtering hook) [Dec 12, 2018]
  • Event.Path for Rename and Move events is now returned in the format of fromPath -> toPath

Chmod event is not supported under windows.

Installation

go get -u github.com/radovskyb/watcher/...

Features

  • Customizable polling interval.
  • Filter Events.
  • Watch folders recursively or non-recursively.
  • Choose to ignore hidden files.
  • Choose to ignore specified files and folders.
  • Notifies the os.FileInfo of the file that the event is based on. e.g Name, ModTime, IsDir, etc.
  • Notifies the full path of the file that the event is based on or the old and new paths if the event was a Rename or Move event.
  • Limit amount of events that can be received per watching cycle.
  • List the files being watched.
  • Trigger custom events.

Todo

  • Write more tests.
  • Write benchmarks.

Example

package main

import (
	"fmt"
	"log"
	"time"

	"github.com/radovskyb/watcher"
)

func main() {
	w := watcher.New()

	// SetMaxEvents to 1 to allow at most 1 event's to be received
	// on the Event channel per watching cycle.
	//
	// If SetMaxEvents is not set, the default is to send all events.
	w.SetMaxEvents(1)

	// Only notify rename and move events.
	w.FilterOps(watcher.Rename, watcher.Move)

	// Only files that match the regular expression during file listings
	// will be watched.
	r := regexp.MustCompile("^abc$")
	w.AddFilterHook(watcher.RegexFilterHook(r, false))

	go func() {
		for {
			select {
			case event := <-w.Event:	
				fmt.Println(event) // Print the event's info.
			case err := <-w.Error:
				log.Fatalln(err)
			case <-w.Closed:
				return
			}
		}
	}()

	// Watch this folder for changes.
	if err := w.Add("."); err != nil {
		log.Fatalln(err)
	}

	// Watch test_folder recursively for changes.
	if err := w.AddRecursive("../test_folder"); err != nil {
		log.Fatalln(err)
	}

	// Print a list of all of the files and folders currently
	// being watched and their paths.
	for path, f := range w.WatchedFiles() {
		fmt.Printf("%s: %s\n", path, f.Name())
	}

	fmt.Println()

	// Trigger 2 events after watcher started.
	go func() {
		w.Wait()
		w.TriggerEvent(watcher.Create, nil)
		w.TriggerEvent(watcher.Remove, nil)
	}()

	// Start the watching process - it'll check for changes every 100ms.
	if err := w.Start(time.Millisecond * 100); err != nil {
		log.Fatalln(err)
	}
}

Contributing

If you would ike to contribute, simply submit a pull request.

Command

watcher comes with a simple command which is installed when using the go get command from above.

Usage

Usage of watcher:
  -cmd string
    	command to run when an event occurs
  -dotfiles
    	watch dot files (default true)
  -ignore string
        comma separated list of paths to ignore
  -interval string
    	watcher poll interval (default "100ms")
  -keepalive
    	keep alive when a cmd returns code != 0
  -list
    	list watched files on start
  -pipe
    	pipe event's info to command's stdin
  -recursive
    	watch folders recursively (default true)
  -startcmd
    	run the command when watcher starts

All of the flags are optional and watcher can also be called by itself:

watcher

(watches the current directory recursively for changes and notifies any events that occur.)

A more elaborate example using the watcher command:

watcher -dotfiles=false -recursive=false -cmd="./myscript" main.go ../

In this example, watcher will ignore dot files and folders and won't watch any of the specified folders recursively. It will also run the script ./myscript anytime an event occurs while watching main.go or any files or folders in the previous directory (../).

Using the pipe and cmd flags together will send the event's info to the command's stdin when changes are detected.

First create a file called script.py with the following contents:

import sys

for line in sys.stdin:
	print (line + " - python")

Next, start watcher with the pipe and cmd flags enabled:

watcher -cmd="python script.py" -pipe=true

Now when changes are detected, the event's info will be output from the running python script.