[gregjor]

I think you’re mixing up the shell program (sh, bash, csh, zsh, etc.) with the Unix/Linux environment. The names of commands (adduser, newgrp) have nothing to do with the shell. Undeleting would get implemented in the file system (multiple solutions to that exist already). grep is a separate executable (with many variants and alternatives), not part of the shell. Man pages are not part of the shell either.