[svlug] Test for network up in a shell script?

[Daniel Pittman]

conover at rahul.net (John Conover) writes:

> Is there a way of testing to see if the network is up and running from a
> shell script?

Not trivially, no.  So, you can try to solve this a bunch of ways, none of
which are absolutely reliable or portable.

If your system has Network Manager installed, the nm-cli tool has a bunch of
reporting capabilities - or you can subscribe to the DBus notifications.
Those give you reasonable information[1] for systems with NM installed and
used.

Otherwise, your best option is to troll the output of /sbin/ip (or ifconfig
and route) to see if there are any interesting looking interfaces up and
with a suitable default route installed.

        Daniel

Footnotes: 
[1]  ...and qdbus is a nice way to interact with it from a shell script; that
     is part of KDE, I think.

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