How can I “watch” a file for modification / change

Question

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• How do I watch a file for changes? 21 answers

I would like to invoke my chrome or firefox browser when a file that I specify is modified. How could I "watch" that file to do something when it gets modified?

Programmatically it seems the steps are.. basically set a never ending interval every second or so and cache the initial modification date, then compare the date every second, when it changes invoke X.

Answer 1

Install inotify-tools and write a simple shell script to watch a file.

Answer 2

As noted, you can use pyinotify:

E.g.:

import webbrowser
import pyinotify

class ModHandler(pyinotify.ProcessEvent):
    # evt has useful properties, including pathname
    def process_IN_CLOSE_WRITE(self, evt):
            webbrowser.open(URL)

handler = ModHandler()
wm = pyinotify.WatchManager()
notifier = pyinotify.Notifier(wm, handler)
wdd = wm.add_watch(FILE, pyinotify.IN_CLOSE_WRITE)
notifier.loop()

This is more efficient than polling. The kernel tells you when it does the operation, without you having to constantly ask.

Answer 3

The other option is to use a checksum. You can use a pattern similar to nose's nosy.py. I use the one from dingus to check my directory for modifications and run the test suite.

Answer 4

Apparently, watchdog works on both Linux & OSX that can be used to monitor for changes in a directory as well with great example documentation. It also works with python3.x in case you don't want to be forced to use python2.x

Answer 5

Use FAM to put a monitor on the file.

Answer 6

use a quick hash function, a cron job, and off you go!

Also, this looks relevant: http://en.wikipedia.org/wiki/Inotify