Monitor folder and run command if there is a file there?

I would like to have my Ubuntu monitor Folder A. If there is a .sh file there, i would like to move that file to Folder B and run it in the background. Is this possible? What should I use to make it happen?

2 Answers

You have a few options:

1. Using inotifywait

#!/bin/bash
# set path to watch
DIR="/path/to/sourcedir"
# set path to copy the script to
target_dir="/path/to/targetdir"
inotifywait -m -r -e moved_to -e create "$DIR" --format "%f" | while read f
do echo $f # check if the file is a .sh file if [[ $f = *.sh ]]; then # if so, copy the file to the target dir mv "$DIR/$f" "$target_dir" # and rum it /bin/bash "$target_dir/$f" & fi
done

Explanation on inotifywait

Set options

To log continuously, you need to set the option -m:

from man inotifywait:

-m, --monitor Instead of exiting after receiving a single event, execute indefinitely. The default behaviour is to exit after the first event occurs. 

To log recursively, you need to set the option -r:

-r, --recursive Watch all subdirectories of any directories passed as arguments. Watches will be set up recursively to an unlimited depth. Symbolic links are not traversed. Newly created subdirectories will also be watched. 

If you do not need recursive monitoring, remove the option.

Events

Furthermore, you need to specify event(s) to trigger:

EVENTS The following events are valid for use with the -e option: access A watched file or a file within a watched directory was read from. modify A watched file or a file within a watched directory was written to. attrib The metadata of a watched file or a file within a watched direc‐ tory was modified. This includes timestamps, file permissions, extended attributes etc. close_write A watched file or a file within a watched directory was closed, after being opened in writeable mode. This does not necessarily imply the file was written to. close_nowrite A watched file or a file within a watched directory was closed, after being opened in read-only mode. close A watched file or a file within a watched directory was closed, regardless of how it was opened. Note that this is actually implemented simply by listening for both close_write and close_nowrite, hence all close events received will be output as one of these, not CLOSE. open A watched file or a file within a watched directory was opened. moved_to A file or directory was moved into a watched directory. This event occurs even if the file is simply moved from and to the same directory. moved_from A file or directory was moved from a watched directory. This event occurs even if the file is simply moved from and to the same directory. move A file or directory was moved from or to a watched directory. Note that this is actually implemented simply by listening for both moved_to and moved_from, hence all close events received will be output as one or both of these, not MOVE. move_self A watched file or directory was moved. After this event, the file or directory is no longer being watched. create A file or directory was created within a watched directory. delete A file or directory within a watched directory was deleted. delete_self A watched file or directory was deleted. After this event the file or directory is no longer being watched. Note that this event can occur even if it is not explicitly being listened for. unmount The filesystem on which a watched file or directory resides was unmounted. After this event the file or directory is no longer being watched. Note that this event can occur even if it is not explicitly being listened to.

You need to prepend each of your events, to be triggered, with -e:

-e moved_to -e create

Of course you can set any event trigger from the list.

With the option --format "%f", we make the command output the filename, which we will use for copying and running the file, combined with the set paths.

How to use

1. Install inotify-tools with apt:

   sudo apt install inotify-tools

2. Copy the script into an empty file, save it as watch_dir.sh

3. In the head of the script, set both the directory to watch and to copy the scripts to
4. Run it, and it starts watching your directory.

2. Using python

Without installing anything extra, we can however do the same however with a small python script:

#!/usr/bin/env python3
import subprocess
import os
import time
import shutil
source = "/path/to/sourcedir"
target = "/path/to/targetedir"
files1 = os.listdir(source)
while True: time.sleep(2) files2 = os.listdir(source) # see if there are new files added new = [f for f in files2 if all([not f in files1, f.endswith(".sh")])] # if so: for f in new: # combine paths and file trg = os.path.join(target, f) # copy the file to target shutil.move(os.path.join(source, f), trg) # and run it subprocess.Popen(["/bin/bash", trg]) print(trg) files1 = files2

How to use

1. Copy the script into an empty file, save it as watch_dir.py
2. In the head of the script, set both the directory to watch and to copy the scripts to (source, target)
3. Run it, and it starts watching your directory.

Note

Both options above assume the scripts do not need any arguments, but that is obviously the case in a setup like this.

Here another version with recursive tree walk...

#!/usr/bin/env python3
import subprocess
import os
import time
import shutil
import threading
source = "/home/pi/Pictures/2020/"
def tree_walk(path): if os.path.isfile(path): if path.endswith("jpg"): subprocess.Popen(["/home/pi/git/rpi_scripts/telegram/tg_send_pic.sh", path]) subprocess.Popen(["rm", path]) elif path.endswith("mp4"): subprocess.Popen(["/home/pi/git/rpi_scripts/telegram/tg_send_video.sh", path]) subprocess.Popen(["rm", path]) else: print("other files...", path)
elif os.path.isdir(path): items = os.listdir(path) for i in items: trg = os.path.join(path, i) tree_walk(trg)
else: print(path, "spec file: socket, FIFO, device file etc.")
tree_walk(source)
#try:
#thread = threading.Timer(3, tree_walk(source))
#thread.start()
#except KeyboardInterrupt:
# print("end")