Check if any IPv4 address is private or public.

ipcheck.bash

#!/usr/bin/env bash
# Brief: Given any IPv4 address check if it is private or public. IPv4 itself is not validated
# Exit code: 0 (private); 1 (public); 2 (neither private nor public)
# Usage: ipcheck <ip_addr>

_test(){
  # Brief: Test if given value if within given limits. No output. Just exitcode.
  local limit1="${1}" value="${2}" limit2="${3}"
  [[ "$(echo -e "${limit1}\n${value}\n${limit2}" | sort -V | awk NR==2)" == "${value}" ]]
  # TODO: May be `-V` is not needed in `sort`
}; export -f _test

ip_addr="${1}"

[[ "${ip_addr}" == 127.0.0.1 ]] && exit 0

_test 10.0.0.0 "${ip_addr}" 10.255.255.255 && exit 0

_test 172.16.0.0 "${ip_addr}" 172.31.255.255 && exit 0

_test 192.168.0.0 "${ip_addr}" 192.168.255.255 && exit 0

[[ "${ip_addr}" == 0.0.0.0 ]] && exit 2

_test 224.0.0.0 "${ip_addr}" 239.255.255.255 && exit 2 # Multicast addresses

exit 1