My tentative introductory guide to navigating a shell interface
(assuming Bash).

🚧 These are rough notes meant for guiding in-person discussions; they
are somewhat terse. 🚧

* Moving around, invoking stuff

With a file browser and a terminal emulator side-by-side:

- ls, cd, mkdir, touch, rm; "/" = root
- globs
- arguments vs options (e.g. ls, diff)
- man, --help
- standard input/output/error: pipes, redirection
- writing scripts (shebangs: see bash(1) § COMMAND EXECUTION)

* Shell language

- ; & (e.g. sleep)
- && || (e.g. grep)
- if, for
- $? (e.g. grep, diff)
- [
- variables
- functions, $@, $1…
- black-box model of a command:
    - inputs: stdin, arguments, environment
    - outputs: stdout, stderr, exit code
    - side-effects: I/O, e.g. files, network
- which, type: keyword ≠ builtin ≠ function ≠ program
- valar quotulis (valar escaepis); e.g. sort operator: [ foo '>' bar ]

* Advanced

- ( ) ≠ { }: try to set variables, or call exit
- (( )), $( )
- glob ≠ regex
- bash extensions
    - [[
    - <( )
    - |&, >&
    - arrays
- job control: fg, bg, jobs, wait, kill, C-z