created: 04/01/2019
updated: 09/03/2019

which, compgen

compgen
    -a: List of user aliases
    -b: List of built-in shell commands
    -c: List of all commands you can run
    -e: List of shell variables
    -k: List of built-in shell keywords
    -A function: List of available bash functions

command-line python tool which combines *top commands

systemd

macOS