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I am looking for a gratis Windows program which will let me selected from a list of running processes and press start/stop and record every file which it accesses in between.
I specifically do not want something that can only show me which files a process currently has open, as that will be too fleeting. Start; record; stop.
I would recommend Process Monitor from SysInternals to do so. It's a general purpose monitoring tool for Windows that can capture events from all programs on the system and show a log of them, incluiding filtering capabilities and other features.
While it's far more advanced than your needs, it certainly can do what you want after configuring the right filters. About your requirements, it's:
As requested in comments, as an example of the desired functionality, I've setup a filter on the firefox.exe process and added the CreateFile and CloseFile operations, so that I watch what files does my browser touches, in real-time. In the main window, the filter icon gives access to this filter options, and also to a button where you can pause capturing of events or resume them.
You can also see the operation performed (open/close a file in this case) and a detail with which file was opened, the time the event happened and what level of access was requested. It also displays failed attempts to open files and why it failed (those can be filtered out too if not wanted). Finally, the menu has an option to save the captured data into a file of various formats for further processing and posterior reloading.
