There are a few solutions:

Option 1: without installing additional software:

You can use a minor script to keep an eye on the Downloads folder, like the watch command does, but make sure it only executes a command when a file is added to the directory. Copy the script below into an empty file, set the path to the folder to watch, and the command to run if a file is added to the directory. Save it as watch.py and make it executable for convenience reasons (so you won't have to use the language prefix). Add it to your startup applications:

- in Lubuntu:

Preferences > Default applications for LXSession, then choose "Autostart"

- or in Ubuntu:

System Settings > Keyboard > Shortcuts > Custom Shortcuts

The add the command to start the script on login:

/path/to/watch.py

The script:

#!/usr/bin/env python



import subprocess

import time



folder = "/path/to/folder/to/watch"

command_to_run = "command_to_run"



def get_drlist():

    return subprocess.check_output(["ls", folder]).decode('utf-8').strip().split("

")



while True:

    drlist1 = get_drlist()

    time.sleep(2)

    drlist2 = get_drlist()

    if len(drlist2) > len(drlist1):

        subprocess.Popen(["/bin/bash", "-c", command_to_run])

Option 2: using inotify-tools:

inotify-tools is a tool you can use (a.o.) to watch a defined folder and take (defined) actions if a new file is added to the folder.

1. Install inotify-tools

   
   
   

   sudo apt-get install inotify-tools
   
   




2. Paste the script below in an empty file, set the folder to watch ("/path/to/your/downloadfolder"), define the command it should run ("command-to-run-your-application") safe it as notifyscript.sh, make it executable for convenience reasons, and add it to your startup applications: (Preferences > Default applications for LXSession, then choose "Autostart". Add the command:

   
   
   

   /path/to/notifyscript.sh
   
   

The script:

#!/bin/bash



while true

do

    fileName=$(inotifywait -r -e create /path/to/your/downloadfolder | sed -r 's/^.*CREATE(,ISDIR)*s+(.*)$/2/g')

    command-to-run-your-application

done

Note that in both cases your application will be called at the moment the file is created, but not yet fully downloaded. If the download is large, it can take some time.

EDIT

Additionally, if the newly added file has to be used as an argument for the command you run when the file is added, use the version below:

It uses the format:

<application> <file>

so the "usual". As an example, I left gedit, so the script will (try to) open the newly added file with gedit.

#!/usr/bin/env python



import subprocess

import time



folder = "/path/to/folder/to/watch"

application = "gedit"



def get_drlist():

    return subprocess.check_output(["ls", folder]).decode('utf-8').strip().split("

")



while True:

    drlist1 = get_drlist()

    time.sleep(2)

    drlist2 = get_drlist()

    for file in [f for f in drlist2 if not f in drlist1]:

            command = application+" '"+folder+"/"+file+"'"

            subprocess.Popen(["/bin/bash", "-c", command])