entr is a Command Line Interfacetool that will watch for changes in the filesystem and execute a command if a file changes on disk.
You pass a list of files to monitor - and then say which command to run.
Example using ls:
ls *.rules | entr -c bash -c "<command>"
Example using rg (which will see all files under version control :
rg --files static/ index.html | entr python3 export.py