- https://github.com/tokenrove/build-your-own-shell/
- https://indradhanush.github.io/blog/writing-a-unix-shell-part-1/
- https://stackoverflow.com/questions/8082932/connecting-n-commands-with-pipes-in-a-shell
- 0 = stdin, 1 = stdout, stderr = 2
- https://www.sarathlakshman.com/2012/09/24/implementation-overview-of-redirection-and-pipe-operators-in-shell
- https://unix.stackexchange.com/questions/159513/what-are-the-shells-control-and-redirection-operators
- https://www.howtogeek.com/440848/how-to-run-and-control-background-processes-on-linux/
- https://wiki.bash-hackers.org/howto/redirection_tutorial
- https://stackoverflow.com/questions/8319484/regarding-background-processes-using-fork-and-child-processes-in-my-dummy-shel