Module shell 

What a shell is: which bash, how it was given its code, and what it had switched on when it joined.

A shell’s own account of itself, read back from the words it wrote. Nothing is inferred from the shape of what it went on to say — bash reports one word for several different things, main standing for a script’s top level in FUNCNAME, an interactive prompt in BASH_SOURCE, and any function a subject cares to name that way.

Bash and what it holds are description alone. Shell pairs that with where the shell sits in the run.

Structs

Bash

Which bash a shell is, and how it was started. Constant for as long as the shell lives — a fork inherits it, and anything that could change it makes a new shell instead.

Flags

$-, as bash wrote it.

Invocation

How bash was given the code it runs. set refuses -i, -c and -s, so all three are settled when the shell starts and cannot have changed by the time anything reads them.

Options

What a shell had switched on at the moment it said so. A snapshot: a subject may set -e at any point.

Shell

A shell in a run: which bash it is, where it sits, and what it had switched on when it joined.

Version

$BASH_VERSINFO, all six elements. What bash behaves like is a function of this, so a reading that has to bend for an older shell has what it needs.