GNU BASH is a branch of the Bourne-shell family. Korn shell is a much more complete and capable variant of Bourne. BASH partially implemented many Korn feature

GNU BASH is a branch of the Bourne-shell family. Korn shell is a much more complete and capable variant of Bourne. BASH partially implemented many Korn features, but not everything. The standard reference is the Korn and Bolsky book (2nd edition). I'm not aware of any free/online resources that are profoundly good. Korn is the very best for scripting.