SOURCES

https://unix.stackexchange.com
https://superuser.com
https://askubuntu.com
https://docs.python.org/2/library/index.html
Debian Manual
Windows Internals, Sixth Edition, Part 1
https://www.webopedia.com
http://wiki.bash-hackers.org/commands/builtin/caller
https://www.cyberciti.biz/open-source/command-line-hacks/compgen-linux-command/