Is there a way to get a list of all the NSPasteBoards and their names on the current system?
I'm wondering if there's some function available (even if private API) to achieve this. Thank you!
No, there's no function to do this, even with private API.
The pboard program (/usr/libexec/pboard) runs as a daemon and manages all shared pasteboards. The NSPasteboard class talks to the pboard daemon using XPC, so to get a list of all pasteboards, pboard would need to handle some XPC message by responding with a list of pasteboard names.
The pboard program is very simple: it initializes various things (logs, sandbox, dispatch queue, mach service) and then calls __CFPasteboardStartServicingConnection, which is actually defined in the CoreFoundation framework. This function ultimately handles each incoming XPC request by calling _CFHandlePasteboardXPCEvent.
Looking at _CFHandlePasteboardXPCEvent in a disassembler (I used Hopper), we can see the complete list of requests supported by pboard:
com.apple.pboard.create
com.apple.pboard.get-counts
com.apple.pboard.barrier
com.apple.pboard.begin-generation
com.apple.pboard.has-entries
com.apple.pboard.register-entries
com.apple.pboard.request-data
com.apple.pboard.refresh-cache
com.apple.pboard.release
com.apple.pboard.unique-promise-file
com.apple.pboard.resolve-all-promises
com.apple.pboard.resolve-pboard-promises
com.apple.pboard.set-data-flags
com.apple.pboard.make-generation-local
None of these has an obvious name like com.apple.pboard.get-pboard-names. Looking at how they're handled, the first thing done by almost all of them is to get a pasteboard name from the event and look up or create the pasteboard with that name.
The only request that I found that doesn't immediately involve looking up a pasteboard by name is com.apple.pboard.resolve-all-promises, which in fact sends the intriguing message +[_CFPasteboardStore copyAllPasteboards]. However, it doesn't send the result, or in fact any result, back to the client, as far as I can tell. And that is the only use of the copyAllPasteboards selector in CoreFoundation.
So, unless you attach to the pboard daemon with a debugger and poke around, you won't find a list of all existing pasteboards. (Attaching to pboard with a debugger requires first disabling SIP, which requires booting your recovery partition.)