Copy unique files from source library into target library

[notdog]

I have two libraries. I'd like to copy files unique to the second library into the first library. The solution I've seen is to add the books from the second library to the first, setting up rules to control the adding process and then using a plug-in to find duplicates. My question is whether a plug-in exists to do something like the inverse: find unique files in the second library, which I can then look over, since errors will be inevitable, and import after that.

Thank you, and apologies if this question has been answered elsewhere.

[theducks]

Copy to Library IS BUILT IN
Preferences Adding Books:Adding Actions (a tab) has options

You run Copy To Library from the SOURCE Library
---
Now switching to Find Duplicates
Right click: Find LIBRARY duplicates:<target library PATH>
So run it FROM the direction where you want to know if the TARGET has a dup

[notdog]

Thanks for your thoughts, TD. Yes, I am aware of the preferences tab with rules governing the addition of books to a library. It is helpful. In the past I've used it to filter duplicates with some success, after which I run the find duplicates plug-in, which will turn up additional match for each setting. If I find no better solution I will proceed that way again for this task.

However if the file names and database entries haven't been cleaned up there can be a heap of false positives and negatives. I wondered if pre-screening for supposedly unique items might let me make less of a mess of my target library once I add the books from the source, which isn't as consistently tidy with titles, authors, tags, and the like. Each library has about 3,000 items, so it will be a hassle to go through, but there may be no better way around it.

[theducks]

?? both use Calibre Metadata , not filenames.
This does NOT use the Add books (filenames) method.
Besides, if you set the Metadata, Calibre has normalized the file-folder anyway.