creating a unix shell?
 

what are some unix programming books that cover how to make a unix shell in C? I hear they were very common decades ago...

They still are, altho only a few are used (bash and zsh are the currently highly developed ones, but some older ones are still around (tho I dont think anyone likes them)).

Read the GNU libc manual, it has a "tutorial" (code snippets, some information, the rest is on you) about how to make a shell. See the section "Job Control", it even has a sub-section "Implementing a Shell", which will get you started on the overall concepts and how its done.