Re: Grabbing connection and link status with nmcli

On Wed, 2017-08-30 at 18:00 +0100, Colin Helliwell wrote:
On 30 August 2017 at 17:51 Thomas Haller <thaller redhat com>

On Wed, 2017-08-30 at 17:17 +0100, colin helliwell ln-systems com

I've not used nmcli in any of its more intricate ways, but are
easily-parsed commands which will allow me to tell whether an
interface is up (a la 'nmcli conn up/down') AND the cable is
('link/carrier state')?
I can grab some hints of the latter with
would prefer an approach that is harmonised through nmcli. Are
couple of sub-commands that can be used rather than parsing the
dev show' output? e.g. to output a couple of specific fields.


how about:

LANG=C nmcli -t -m tabular -f WIRED-PROPERTIES.CARRIER device show


Thanks Thomas, that's the hints I was looking for :)
I see I can do similar with GENERAL.STATE, for whether the connection
has been taken up/down, and then logically And the two. 


you can also request them at once:

LANG=C nmcli -t -m tabular -f WIRED-PROPERTIES.CARRIER,GENERAL.STATE device show "$DEV"

but that doesn't seem very nice for parsing either.

But is there a way to be assured of what the textual result will be
for this one: 100/30/20, "connected"/"disconnected"/"unavailable" ?
It could be a headache if NM changes one day and alters the

In principle it should be stable, and we care very much about that.

However, the current output format has some issues.

- in --terse mode we also translate the output. I think that is wrong,
and we might fix it in future. The future proof workaround for this is
setting LANG=C

- as you see, the output for state is for example "20 (unavailable)". I
think that is bad, I wish we would fix it to either being only numeric
or only the descriptive name. At least, in --terse mode, which is
especially intended for parsing. I wish we would fix that one day, but
we probably won't because it might break scripts.
Especially the output of `nmcli connection show "$CON` is inconsistent
about how enum values are printed (numeric, numeric + text, text, text
+ numeric). I wish that could be cleaned up, but we probably won't do
that. Some minor adjustments though happend in the past, e.g.

- I think using the --terse most is better for scripting. We might be
more willing to change the pretty-output, but pay special attention to

- I don't like the current output modes much. None of the modes is very
suited for parsing, because they don't escape newlines in the output.
One day, I think we should escape them. Probably we'll have to add a
special flag, so that the existing format doesn't change.

in short: Yes, it's supposed to be stable.


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