The problem with making a shell more like a "real" interpreter REPL is the purpose of a shell: Running arbitrary programs not known to the author of the shell, such that any unknown word in a shell script is probably the name of a program as opposed to a misspelled reserved word or variable name. Those programs having arbitrary command-line arguments and having to operate on files with arbitrary names is another complexity.

It's interesting to see how so many things grow into each other. A shell is what you say, but there are many efforts to change that. Bash has its magic autocomplete which knows about options of many, many programs. Powershell has an object-model with knowledge of many of its commands.

It has been done. See xonsh a python shell which manages the distinction you mention.

Also see scsh and rash for scheme

Fish for non posix but sane syntax

> Can we actually improve the POSIX shell?

PowerShell?

No, that won't work.

  $ ll /bin/dash
  -rwxr-xr-x 1 root root 85368 Jan  5 09:52 /bin/dash

If you can make Powershell in a binary that size, then you have a valid point.

But why? Storage is much cheaper today than it was in the 80s. While I myself don’t like huge Electron apps, trying to save every byte of storage is simply not worth it.

Embedded applications on smaller systems are why.

The POSIX shell is common, from the largest supercomputer down to the smallest ARM.

I don't think that there will be any new developments covering that full scope.

Many embedded systems hardly have any shell, and even when they do, it isn't bash (which isn't POSIX anyway), rather a tiny subset with the basic tooling for maintenance.

Embedded systems don't exclude PowerShell from being a replacement for POSIX shells. Maybe embedded systems should not strive to be POSIX.