As a contrast, in the DOS world the file COMMAND.COM provided both the shell as well as most of the basic file management commands which would be separate files

As a contrast, in the DOS world the file COMMAND.COM provided both the shell as well as most of the basic file management commands which would be separate files on Unix-like systems (cp, ls, mkdir, mv, rm, rmdir, etc.); and some specialised DOS-compatible systems had the whole basic OS including the kernel, device drivers, and shell along with its builtins in a single flat-loaded binary.