[Raspberry Pi] How to continuously monitor directories and run arbitrary shells with hooks for changes

With Raspberry Pi 3B (hereinafter: Raspberry Pi), I would like to ** monitor the specified directory ** and run arbitrary processing when it is updated.

--Hook: Image is saved in A directory --What to do: Synchronize the state of A and B directories

Specifically, use ** inotify-tools ** to do something like the above.

Install inotify-tools

Install with apt-get.

$ sudo apt-get install inotify-tools

Monitor with the inotyfy wait command

ʻInotyfywait -e [Event] [Monitoring directory] `

Specify the specific event and the directory to be monitored with the inotfywait command. This time, the moved_to (moved into the target directory) event is monitored and processed.

inotify_single.sh

#!/bin/sh

inotifywait -m -e moved_to A | \
    rsync -rv A B

I'm using the rsync command to synchronize A and B.

About the -m option

If you do not add the -m option, inotifywait will end when the first event is issued, so it is added.

Continuously monitor

If this is left as it is, monitoring will end when a series of events are notified, so correct the process.

inotify_continuous.sh

#!/bin/sh

inotifywait -m -e moved_to A | \
    while read _; do
        rsync -rv A B
    done

In this way, the while statement is used to continuously monitor.

environment

• Raspberry Pi 3B
• Raspbian GNU/Linux 9.8 (stretch)
• inotifywait 3.14[^1]

[^ 1]: You can check the version of inotifywait with ʻinotifywait -hl`

reference

-Monitor files and directories with inotify-tools