todo

some topics that come up in questions and need to be explained well:
- quoting
- different kinds of tests, different kinds of patterns
- env, global and local vars, scoping
- parsing "layers": what is bash syntax, what is command arguments and data/ literal vs. syntactical etc.


advanced topic ideas:
- how prefixing functions with variable assignments makes a "local" variable scope without needing a subshell for it, and how unset'ing that local variable in the function does not affect the global scope.