using inotify to monitor access to a file

Question

I would like to have a trigger and when a particular file is accessed by some process, I would like to be notified (i.e. a script should be run). If I understand correctly, this could be achieved with inotify.

If I have a file /foo/bar.txt how would I set up inotify to monitor that file?

I am using Debian Wheezy with kernel 3.12 (my kernel has inotify support)

Answer 1

According to Gilles on Super User:

Simple, using inotifywait (install your distribution's inotify-tools package):

while inotifywait -e close_write myfile.py; do ./myfile.py; done

This has a big limitation: if some program replaces myfile.py with a different file, rather than writing to the existing myfile, inotifywait will die. Most editors work that way.

To overcome this limitation, use inotifywait on the directory:

while true; do
  change=$(inotifywait -e close_write,moved_to,create .)
  change=${change#./ * }
  if [ "$change" = "myfile.py" ]; then ./myfile.py; fi
done

Answer 2

The basic shell interface to inotify is inotifywait from inotify-tools.

To monitor all accesses to a file:

inotifywait -mq --format '%e' /path/to/file |
while IFS= read -r events; do
  /path/to/script "$events"
done

Your script is called with a comma-separated list of simultaneous events, each time something happens to the file (read, write, close, …).