How-To launch a command everytime a file changes

Using inotify

Source: https://superuser.com/questions/181517/how-to-execute-a-command-whenever-a-file-changes

Prerequisite:

sudo apt install inotify-tools

Example: copy a file to another server whenever it changes (e.g. for easy web development):

while inotifywait -e close_write myfile.py; do scp ./myfile.py remote-server:/var/www/html/ ; done