UNIX for Dummies Questions & Answers

I'm going through my UNIX book and came across a section on Customization and Subprocesses.

Can someone tell me what a subprocess is -- for example, when the book says "Which shell 'thing' are known to subprocesses" what exactly does it mean? The book just talks about it without defining it -- very frustrating, because the following section doesn't make a lot of sense to me.

What is the difference between a bash program and an interactive shell? (I think an interactive shell is one that accepts user input, right?)

A subprocess is a child process, i.e. a process that has been launched by its parent to which it is a subprocess.

An interactive shell is a command line interpreter reading your input line by line and prompting you when a command is done.

A bash program (or more generally a shell script) is reading its commands not from your keyboard but from a text file containing them.

Can you give me an example of a process and a subprocess? I'm still not quite clear -- it's still a little confusing when the word I don't understand the definition of is used in the definition.

Being a subprocess denotes a relationship, not a specific property.
All processes are subprocesses of their parent process, except init which is launched by the kernel itself.

But, with all due respect, that doesn't make it any clearer.

Can you tell me what a process is, and give an example of one, and then explain/give an example, or tell me then what the subprocess would be? I'm just learning about this kind of stuff and it's still confusing.

Quote from Wikipedia I can't think of a better explanation, and it would have helped if you stated from the start that you don't know what a process is. We were under the assumption that you're only unclear on the concept of a sub-process.

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.