# Shell

## Variables

All active variables can be seen by running `env`.

* `$HOME` - Expands to the path of my home folder.
* `$PS1` - Variable that represents my command prompt line.
* `$PATH` - Special environment variable that contains the command path (list of system directories that the shell searches when trying to locate a command).

## Notes

* Scripts are run in subshells, and nothing is shared "upwards". That's the difference between running a script and sourcing one. A sourced (imported) script is run in your own script's namespace.
* In shell everything is a string.
* Children never touch parent environment. It can only if it runs as part of the current process (source, function, alias).
* Pipes are used to connect one process's output with another process’s input.
* `/etc/paths.d` define paths to add to `$PATH` globally to all users.

## Links

* [Explain Shell](https://www.explainshell.com/)
* [Introduction to POSIX Shell](http://drewdevault.com/2018/02/05/Introduction-to-POSIX-shell.html)
* [Yoshua's notes](https://yoshuawuyts.gitbooks.io/knowledge/content/unix/shell.html)
* [Shell Auto-completion Systems](http://dundalek.com/entropic/shell-auto-completion/)
* [Shell and Scripting (2019)](https://hacker-tools.github.io/shell/)
* [ShellCheck](https://www.shellcheck.net) - Finds bugs in your shell scripts.
* [Rash](https://github.com/willghatch/racket-rash) - The Reckless Racket Shell.
* [Eternal Terminal](https://github.com/MisterTea/EternalTerminal) - Remote shell that automatically reconnects without interrupting the session.