I understood that Stephen Borne's love of ALGOL was the chief structural influence of the POSIX shell (so much so that he used the C preprocessor to turn his source code into fake ALGOL).

"Stephen Bourne's coding style was influenced by his experience with the ALGOL 68C compiler that he had been working on at Cambridge University... Moreover, – although the v7 shell is written in C – Bourne took advantage of some macros to give the C source code an ALGOL 68 flavor. These macros (along with the finger command distributed in Unix version 4.2BSD) inspired the International Obfuscated C Code Contest (IOCCC)."

https://en.m.wikipedia.org/wiki/Bourne_shell

Do you have some writing on this? I'd love to read it.