¹ https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V...
² https://pubs.opengroup.org/onlinepubs/9699919799/idx/utiliti...
³ https://youtu.be/kTcRRaXV-fg
> The whence command is a Korn Shell feature that tells how a name would be interpreted by the shell: it detects commands and aliases, and searches your path.
[1] http://www.robelle.com/smugbook/whence.html