Earlier quoted context omitted.
I know about that utility -- still not shell though. The fact that you need a utility to make such a simple task readable is pointing to the shell language lacking.
By your own logic, your own UNIX solution to the file renaming problem is "not shell" since it uses the mv "utility". Or do you mean rename is not POSIX? The shell language certainly is lacking for almost anything beyond its original purpose of gluing together pipelines/graphs of UNIX commands; it's a largely unintentional DSL from the time before many modern notions of language ergonomics had become established. The…
https://pubs.opengroup.org/onlinepubs/009695399/functions/re...
mv is basically just a shim over rename so I don't see your point.
Shell may be to glue things together but it's supposed to also be a decent language for doing file/filename related things.