netplan needs version numbering

[Gordon Harris]

If you're going to deprecate formerly good features (e.g. gateway4:) then netplan should have and be able to output a version number so we can determine the syntax to use.

e.g.:

netplan --version

..should return something.

[Lukas Märdian (slyon)]

The netplan version information was explicitly removed a long time ago (2019) in favor of feature flags:
https://github.com/canonical/netplan/commit/9ea105bef2cea28916213aad93a37ea85d89fdbc

The gateway4: field is still kept around for compatibility reasons (deprecated, though), especially on stable releases.

You can still use your package manager to check netplan's package version, e.g.:
apt show netplan.io

[Gordon Harris (wgordonharris)]

Thanks for that.

So, Re use feature flags:

NETPLAN_USE_ROUTES="$(netplan info | grep -c default-routes)"

And, Re use package manage to check netplan's package version:

NETPLAN_VER="$(dpkg-query --showformat='${Version}\n' --show 'netplan.io' | sed -e 's/-.*$//')"

[Adam Collard (adam-collard)]

We need something like `--version` as a cheap command to run to see if netplan is installed in any given environment

--version, like --help is a GNU standard:

https://www.gnu.org/prep/standards/html_node/Command_002dLine-Interfaces.html

It is inappropriate to use it for feature detection, which `netplan info` handles just fine.