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?

Solution 1:

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.