findroute

#!/bin/bash
# (c) 2020 Leif Sawyer
# License: GPL 3.0 (see https://github.com/akhepcat/)
# Permanent home:  https://github.com/akhepcat/Miscellaneous/
# Direct download: https://raw.githubusercontent.com/akhepcat/Miscellaneous/master/findroute

if [ -z "$(command -v seq)" ]
then
 seq() {
  local start=${1:-2}
  local step=${2:-1}
  local end=${3:-254}

  if [ "$#" -eq 2 ]; then
    end=$step
    step=1
  fi

  if [ "$step" -gt 0 ]; then
    while [ "$start" -le "$end" ]; do
      echo "$start"
      start=$((start + step))
    done
  else
    while [ "$start" -ge "$end" ]; do
      echo "$start"
      start=$((start + step))
    done
  fi
}
fi

links=$(ip link show | grep '^[0-9]' | grep -vw lo: | wc -l)
if [ ${links:-999} -lt 2 ]
then
	echo "all routes:  $(ip route show default)"
	exit 0
fi

IP=${1//[^0-9a-fA-F.:]/}

if [ "$1" != "${IP}" ]
then
        echo "invalid IPv4 or IPv6 address"
        exit 1
fi

if [ -z "${IP}" ]
then
        echo "IPv4/IPv6 address to find route for?"
        exit 1
fi

if [ "${IP##*:*}" != "${IP}" ]
then
   six="-6"
   tcidr=128
else
   six=""
   tcidr=32
fi

for cidr in $(seq $tcidr -1 0)
do
        status=$(ip ${six} route show ${IP}/${cidr})
        if [ -n "${status}" ]
        then
                status=${status// via/, routing via}
                echo "${IP} contained in ${status}"
                exit 0
        fi
done
echo "unable to determine route. that's odd"