My apologies -- but your explanation is fine. So I'm guessing that a subprocess consists of other executions required to carry out the primary executions of said instructions?

so when something is 'known' to a subprocess, it means what?

Here are the paragraphs that confused me:

"Some of the variables discussed above are used by commands you may run -- as opposed to the shell itself -- so that they can determine certain aspects of your envrionment. The majority, however, are not even known outside the shell.

This dichotomy begs an important question: which shell "Things" are known outside the shell, and which are only internal? This question is at the heart of many misunderstandings about the shell and shell programming. Before we answer, we'll as it again in a more precise way: which shell "things?" are known to subprocesses? Remember that wenever you enter a command, you are telling the shell to run that commmand in a subprocess; furthermore, some complex programsmay start their own subprocesses. Now for the answer, which (like many UNXI concepts) is unfortunately not as simple as you might like. "A few things are known to subprocesses, but the reverse is not true: subprocesses can never make these things known to the processes that created them.

Which things are know depends on whether the subprocess in question is a bash program or an interactive shell. If the subprocess is a bash program, then it's possible to propagate nearly every type of thing we've seen in this chapter -- options and variables -- plus a few we'll see later."

To which I respond: Huh?

I ask because the following section i the book concerns what are called environment variables, and if I know what a subprocess is, then I can make sense of the section better.

Maybe I should have just quoted this at the beginning, come to think of it. Apologies again.