How to tell which repositories provide which packages?

[Ralf Mardorf]

On Wed, 2021-01-06 at 19:52 +0100, Ralf Mardorf via ubuntu-users wrote:
> On Wed, 6 Jan 2021 12:41:39 -0500, Little Girl wrote:
> > It looks like it must be an unsigned integer, but it can be ommitted
> > and, if so, is assumed to be a zero:

PS: The assumption of "0" for packages without an epoch describes the
sort order of the package management. But if we use the grep command to
recognize, to distinguish, if the package version is "(none)" or an
existing package, with real versioning, without using grep's inverted
match option, the "0" is just imaginary, it doesn't exist for grep.

The inverted match seems to be the best thing to do, since "(" is
definitively no valid versioning char. To keep the script human readable
it makes sense to use "(none)" instead of "(" only.

> > https://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-version
> 
> Thank you for doing this work. It's still not clear to me.
> 
> The epoch must start with a digit, but most packages don't use an
> epoch at all. 
> 
> "The upstream_version may contain only alphanumerics [6] and the
> characters . + - ~ (full stop, plus, hyphen, tilde) and should start
> with a digit. If there is no debian_revision then hyphens are not
> allowed."
> 
> "[6] Alphanumerics are A-Za-z0-9 only."
> 
> "should start" but IIUC they could start with a letter. A-Za-z seems to
> exclude umlauts and other exotic signs. IIUC theoretically it could even
> start with a full stop, plus, or tilde. IOW usage of "[:alnum:]" is
> likely better than usage of "[:digit:]", probably no package version
> starts with a full stop, plus, or tilde, but perhaps with "alpha",
> "beta", "git", "af12de" hex numbers etc.
>