Real Time File Sync - Mirroring Locally

I need to sync a number of files in one folder to other folder on the same machine (no sub folders involved). I have tried hard linking i.e. ln dir1 dir2 but it is not sync'ing/replicating. Everything I have read so far is about real time syncing between servers - I do not want that. I simply(?) want the files (4 of them) in dir1 to be duplicated in dir2 whenever one of them in dir1 changes.

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