The Bourne Again shell is not based upon the Korn shell. There's a very big clue...

chubot · 2025-06-26T13:05:25 1750943125

I'm saying the behavior of bash is largely based on ksh. See

https://pages.oils.pub/spec-compat/2025-06-19/renamed-tmp/sp...

(which I created)

Even the upcoming bash 5.4 implement ksh command sub ${ echo hi; }, which is more evidence that bash is based on ksh.

They're still implementing ksh 35 years later ...

JdeBP · 2025-06-27T09:46:50 1751017610

The unequivocal direct evidence that the Bourne Again shell is based upon the Bourne shell is Richard Stallman saying so, back when it was written in 1988.

"Foundation staff member Brian Fox is now implementing an imitation of the Bourne shell."

chubot · 2025-06-27T14:57:57 1751036277

ksh is a superset of Bourne shell

https://www.oilshell.org/archive/ksh-usenix.pdf

bash implemented essentially all Bourne shell features a long time ago -- and for the last decade+, and currently, it's implementing ksh features

I'm not sure why it's hard to hold those 2 ideas in your head at the same time