CommandBox has a powerful utility that can be used to watch a folder of files for changes and fire arbitrary code when changes happen. The utility will block execution of the command until the user stops it with Ctrl+C. To use a watcher in your command, there is a method called watch() in the base command class that you can call. It has a nice DSL of chainable methods to configure it.
Here's a rundown of the methods used above in the DSL.
paths( ... ) - Receives a comma-delimited list of globbing patterns to watch for changes. (defaults to **)
inDirectory( ... ) - Set the base directory that the file globs are relative to. (defaults to current working directory)
withDelay( ... ) - Set the number of milliseconds between polling the file system. (defaults to 500 ms)
onChange( ... ) - Pass a closure to be executed when a change has occurred.
start() - Starts the watcher. Always call this at the end of the DSL chain