[GENERAL] Associating a basebackup and it's .backup WAL file

Hi

Given a basebackup base.tar.gz and an archive of WAL files, is there any
way to find out which .backup WAL file is associated with the basebackup
from command line?

My use case is for a retention policy bash script which:

-deletes all basebackups older than X days

-runs pg_archivecleanup for the oldest basebackup

I just don't know how to find out which WAL to feed to pg_archivecleanup
at this point.