See what process is using a file in Mac OS X

Question

I would like to be able to track a file and see which process is touching that file. Is that possible? I know that I can see the list of open processes in activity monitor

Answer 1

lsof will list open files, but it can be a bit awkward for momentary touches (eg, if the file isn't open when lsof runs, it doesn't show).

I think your best bet would be fernLightning's fseventer.app. It's "nagware", and allows you to watch (graphically) the fsevents API in real-time.