But, every time I see examples of how to write sh scripts properly, it makes me wonder if this is just the wrong way to look at the world. Maybe it would be easier to extend Python down to make it better for command line use. Xonsh or something.
Something like Perl's IPC::Run.
Also, more shell-relevant stuff in the default distribution, so that one doesn't need to care about any modules (which is the primary reason for using bash or even sh, those are installed practically everywhere along with at least coreutils and stuff). Edit: examples that a standard python doesn't really do would be quick and easy recursive directory traversal and doing stuff to files found there (like the unix 'find' tool), archive (de)compression, file attribute operations (not only simple permissions but also ACLs, xattrs, mknod, etc).
But the sister comment clarified it in another way, so this maybe irrelevant.
Convenience features, like ls and other classic shell commands being run without parentheses would have to be handled… I’m not breaking any new ground here, actually this has gotten me to look into xonsh and it looks pretty decent.