How to tell which repositories provide which packages?

[Ralf Mardorf]

On Wed, 6 Jan 2021 10:42:14 -0500, Little Girl wrote:
>https://paste.ubuntu.com/p/2X2NWZkv4m/

"It's a collection of commands for getting PPA information."

Actually it's a collection of scripts, just not in the sense of a file
that starts with a #!/bin/sh. However, the combination of commands,
even by not using them in a file, but directly typed to command
line, are scripts. Aren't they?

Regarding the "[:digit:]", maybe somebody knows the convention for
Ubuntu/Debian package versioning? Must the first char of the
versioning always be a number? Or else, is it allowed to use a letter
or any other char as first versioning char?