[Cialug] Just Tell Me The IP!

[Scott Yates]

You might try the output of "route".  I think it is more universal, and
might be easier to parse out.

On Thu, May 21, 2020 at 12:11 PM Todd Walton <tdwalton at gmail.com> wrote:

> I'm running a mix of CentOS, Amazon Linux, and Ubuntu. The CentOS servers
> span three generations, the Amazon Linux, like, four. And you know what's
> surprisingly complicated to do across a variety of distributions and
> versions? Tell me the IP of the server I'm on. Well, if I'm "on" the
> server, it's just a couple of quick commands and an eyeball. But I need a
> way to do it by script.
>
> Problems include:
>
> * The "ip" command shows up in three different locations, depending on
> distribution.
> * The "ifconfig" command shows up in 2 different locations.
> * You can run those just fine sans sudo, but sbin is typically not in a
> user's PATH.
> * Network device names vary across distributions.
> * Some servers have multiple IPs. I need one, it needs to be from a
> "physical" device, and it needs to be the same one every time.
> * ip's output varies across versions
> * ip has json output, but only for a couple years now, so it's not in any
> of my distros </grouse>
>
> Is there just no reliable way to get a server's "primary" IP that works
> across distros and distro versions? I wish there was something like
> "hostname" that just spat back /the IP address/.
>
> This is what I'm doing right now:
>
> HOSTIP=$(find /sys/devices -type d -name 'net' -not -path '*/virtual/*'
> -print | xargs -I% find % -mindepth 1 -maxdepth 1 -exec basename {} + |
> grep -P '^e' | xargs -n1 ifconfig | grep 'inet ' | tr -s ' ' | sed -e
> 's/^[[:space:]]\+//g' -e 's/addr://g' | cut -d\  -f2 | sort | head -n1)
> if [[ -z $HOSTIP ]]; then HOSTIP='$(ifconfig | grep 'inet ' | tr -s ' ' |
> sed -e 's/^[[:space:]]\+//g' -e 's/addr://g' | cut -d\  -f2 | sort | head
> -n1)'; fi
> if [[ -z $HOSTIP ]]; then HOSTIP='127.0.0.1'; fi
>
> It's fraught with disappointment, but less than anything else I've tried so
> far.
>
> (Also, I didn't realize until this little adventure that xargs will always
> run once, even without input, unless you explicitly tell it not to. Ugh.)
>
> --
> Todd
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