See what process is using a file in Mac OS X

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 but I think it's happening to quickly for me to see it. The reason for this is I'm using a framework and I think the system version of the framework is being used instead of the debug version and I'd like to see which process is touching it.

That's simple: sudo fs_usage | grep [path_to_file]

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.

But I spent 2 minutes Googling and found your answer here.

$ lsof | grep [whatever]

Where [whatever] is replaced with the filename you're looking for. With this, you can see which program is desperately holding onto your about-to-be-trashed file. Once you exit that program, your trash will empty.

The faster way is:

$ lsof [path_to_file]

This solution doesn't require the root password and gives you back the following, clear, result:

COMMAND    PID USER   FD   TYPE DEVICE SIZE/OFF     NODE NAME
Finder     497  JR7   21r   REG    1,2   246223 33241712 image.jpg
QuickLook 1007  JR7  txt    REG    1,2   246223 33241712 image.jpg