rpitx | RF transmitter for Raspberry Pi

This is actually quite a difficult problem to get 100% perfect, but it is possible to get pretty close.

It is easy to get all the files in a directory, and it is easy to use inotifywait to get iteratively informed of new files being placed into the directory. The issue is getting the two to be consistent. If inotifywait isn't started until all the files have been processed (or even just listed), then you might miss new files created between the listing and the invocation of inotifywait. If, on the other hand, you start inotifywait first, then a file created after the invocation of inotifywait and the extraction of the current file list will be listed twice.

Since it is easier to filter duplicates than notice orphans, the recommended approach is the second one.

As a first approximation, we could ignore the duplicate problem on the assumption that the window of vulnerability is pretty short and so it is probably unlikely to happen. This simplifies the code, but it's not that difficult to track and eliminate duplicates: we could, for example, store each filename as the key in an associative array, ignoring the file if the key already exists.

We need three processes: one to execute inotifywait; one to produce the list of initial files; and one to handle each file as it is identified. So the basic structure of the code will be: