#!/usr/bin/env bash
:<<'_COMMENTS_'
===============================================================================

          FILE:  get-inet-addrs
         USAGE:  Make file executable or: bash /path/to/get-inet-addrs
   DESCRIPTION:  For network interfaces on a GNU/Linux host with ipv4 addresses
                 assigned get network address info by querying the /proc
                 pseudo-filesystem.
       OPTIONS:  ---
  REQUIREMENTS:  ---
          BUGS:  ---
         NOTES:  Credit: Felix Hauri (www.f-hauri.ch)
                 see http://stackoverflow.com/questions/5281341
                 Version 1.1 cleans up script layout; no code changes.
        AUTHOR:  G. D. LaBossiere, Xview Solutions Inc.
         EMAIL:  code@XviewSolutions.com
       VERSION:  1.1
       CREATED:  2014-07-06 (Version 1.0)
      REVISION:  2022-10-19
       LICENSE:  GNU GPL v3 <http://www.gnu.org/licenses/gpl-3.0.txt>
===============================================================================
_COMMENTS_
#------------------------------------------------------------------------------
#  functions
#------------------------------------------------------------------------------
#  accepts 2 params; invert the order (endianness) of 2nd param's 4 hex values
#+ (8 characters), convert to decimal string, assign value to 1st param
hex_to_decimal() {
  printf -v ${1} "%d\n" "0x${2:6:2}${2:4:2}${2:2:2}${2:0:2}"
}
#------------------------------------------------------------------------------
#  accepts 4 params; convert 2nd, 3rd and 4th params from decimal strings to
#+ ipv4 addresses (4 octets) and assign values to 1st param
decimal_to_network() {
  local decVal netVal
  netVal=${1}
  shift
  for decVal; do
    printf -v ${netVal} "%s %s.%s.%s.%s" "${!netVal}" "$(($decVal>>24))" \
      "$(($decVal>>16&255))" "$(($decVal>>8&255))" "$(($decVal&255))"
  done
}
#------------------------------------------------------------------------------
#  accepts 2 params; convert 2nd param decimal string to netmask bit value and
#+ assign value to 1st param
decimal_to_bits() {
  local int
  for ((int=0; int<32 && (1&${2}>>(31-int)); int++)); do :; done
  printf -v ${1} "%d" "${int}"
}
#------------------------------------------------------------------------------
#  main
#------------------------------------------------------------------------------
addressDecVal=""
eachConnection=""
netmaskDecVal=""
networkDecVal=""
printFormat=""
thisConnection=()
thisAddress=""
thisMask=""
thisRoute=()

while read -a thisRoute; do
#  lines in /proc/net/route where Gateway is 00000000 and Mask is not 00000000
  if [[ ${thisRoute[2]} == "00000000" ]] && \
    [[ ${thisRoute[7]} != "00000000" ]]; then
#  convert hex values to decimal strings
    hex_to_decimal networkDecVal  ${thisRoute[1]}
    hex_to_decimal netmaskDecVal ${thisRoute[7]}
#  no double-brackets '[[ ]]' else the test will fail
    if [ $((networkDecVal&netmaskDecVal)) == ${networkDecVal} ]; then
#  loop thru /proc/net/{tcp,udp}
      for eachConnection in /proc/net/{tcp,udp}; do
#  chop each line into fields delimited by colons, spaces, tabs or newlines
        while IFS=': \t\n' read -a thisConnection; do
#  if 'local_address' field starts with valid hex character...
          if [[ ${thisConnection[1]} =~ ^[0-9a-fA-F]*$ ]]; then
#  ...convert hex value to decimal string and...
            hex_to_decimal addressDecVal ${thisConnection[1]}
#  ...pop up 3 levels; no double-brackets '[[ ]]' else the test will fail
            [ $((addressDecVal&netmaskDecVal)) == ${networkDecVal} ] && break 3
          fi
        done < ${eachConnection}
      done
    fi
  fi
done < /proc/net/route

#  get netmask bit value
decimal_to_bits thisMask ${netmaskDecVal}
#  convert decimal strings to network octets
decimal_to_network thisAddress ${addressDecVal} ${networkDecVal} \
  ${netmaskDecVal}
printf -v printFormat '%-12s: %%s\\n' Interface Address Network Netmask \
  Mask\ Length
#  ${thisRoute[0]} holds the interface name, e.g. eth0
printf "${printFormat}" ${thisRoute[0]} ${thisAddress} ${thisMask}\ bits
exit 0