DC/OS ip-detect script for "deterministic network interfaces naming"

ip-detect

#!/usr/bin/env bash
set -o nounset -o errexit
export PATH=/usr/sbin:/usr/bin:$PATH

function msg { out "$*" >&1 ;}
function out { printf '%s\n' "$*" ;}

function showint {
  msg $(ip addr show $1 | grep -Eo '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | head -1)
}
if [[ -d /sys/class/net/eth0 ]]; then
  showint "eth0"
else
  # udev names network devices by their MAC addresses
  # chooses first enp device (so far best heuristic)
  showint $(ls -d /sys/class/net/enp* | tail -n +1 | cut -d \/ -f 5)
fi