How to automatically run a script when the contents of a directory changes in Linux?

Question

I want to automatically run a script whenever new files are copied into a particular directory. In other words, is there a way in Linux to "watch" a directory for changes and then run something in response to the change?

Answer 1

If you're lucky enough to be on a debian-based distribution, apt-get install dnotify. Other distributions probably have something similar - look for the dnotify name.

dnotify is a simple program based on Linux kernel 2.4.19+'s dnotify API. dnotify can execute a specified command each time the content of a specific directory changes. It is run from the command line and takes two arguments: one or more directories to monitor and a command to execute whenever a directory has changed. Options control what events to trigger on: when a file was read in the directory, when one was created, deleted and so on.

If you want to handle this within your own program, dnotify is also the API you want to use.

Answer 2

You can run a script with the inotify-tools, something like this. It will watch the directory for changes in modified files, new files, and deleted files, then it will execute the script.

#!/bin/sh
while inotifywait -e modify -e create -e delete /home/me/code; do
    rsync [options] /home/me/code/ /media/nfs/code/ 
done

Answer 3

incron is basically what you want, I think. It uses inotify as the notification mechanism (which, as others have pointed out, supercedes dnotify), but doesn't require a script that continuously runs, using inotifywait or similar (although, obviously, the incron daemon is running all the time). System-wide 'crontabs' and user 'crontabs' are supported in a similar way to standard cron, but rather than specifying times as triggers, inotify events and files/directory names are used.

incron is packaged for many distributions, including Ubuntu and Debian, I believe.