Not an expert here either. I will say using a book as a corpus does remind me of LWIC software. How the shuf command was executed to generate a cryptologically safe passphrase doesn't necessarily seem to be extremly secure. Given that it's only to the 6th degree, I'm sure permutations can be computed though given the corpus as a database. I might be wrong technically speaking I understood your command structure but do not yet know intricacies of mathematical computational rates.