mm-mac2ipv4.bash

#!/bin/bash
#
# © 2016 Meta Mesh Wireless Communities. All rights reserved.
# Licensed under the terms of the MIT license.
#
# AUTHORS
# * Jason Khanlar
#

function normalize-ipv4-octet-2 {
  ((ip2=$1 % 32 + 96))
}

function normalize-ipv4-octet-4 {
  ((ip4=$1 - ($1 % 64 - $1 % 32)))
}

function list-all {
  mac1=DC
  mac2=9F
  mac3=DB
  mac4=00
  mac5=00
  mac6=00

  ip1=100
  ip2=64
  ip3=0
  ip4=0

  for octet in `seq 0 255`;do
    normalize-ipv4-octet-2 $octet

    mac4=$(printf "%02X\n" $ip2)

    # Format IP address
    ip="$ip1.$ip2.$ip3.$ip4"

    # Format MAC address
    mac="$mac1:$mac2:$mac3:$mac4:$mac5:$mac6"

    # Pad with space
    space=`printf '%*s' "$((15 - ${#ip}))"`

    # Output matching IP address and MAC address
    echo "$ip $space=> $mac"
  done
}

function usage {
  echo "Usage: $0 <MAC address>"
  echo "Usage: $0 --list-all"
  echo
  echo "examples:"
  echo "  $0 DC:9F:DB:CE:13:57"
  echo "  $0 DC-9F-DB-CE-13-57"
  echo "  $0 DC 9F DB CE 13 57"
  echo "  $0 dc 9f db ce 13 57"
}

# Check for --list-all, otherwise proceed

while getopts ":-:" opt; do
    if [ $OPTARG = "list-all" ]; then
        list-all
        exit
    fi
done

if [[ "$*" =~ -*- ]]; then
    usage
    exit 1
fi

# Proceed if not --list-all

# Get # of arguments passed to this script
args=$#

# # of arguments should be 1 or 6
# 1 -> DC:9F:DB:CE:13:57 -or- DC-9F-DB-CE-13-57
# 6 -> DC 9F DB CE 13 57

if [ $args -eq 1 -a ${#1} -eq 17 ]; then
  # Split 1 argument into 6 separate arguments, 1 for each octet
  # and pass the 6 arguments to a new instance of this script
  $0 `echo $1 | tr ":-" " "`
  # After the new instance completes, make sure to end this one
  exit
elif [ $args -eq 6 ]; then
  mac1=$(echo $1|tr '[a-z]' '[A-Z]')
  mac2=$(echo $2|tr '[a-z]' '[A-Z]')
  mac3=$(echo $3|tr '[a-z]' '[A-Z]')
  mac4=$(echo $4|tr '[a-z]' '[A-Z]')
  mac5=$(echo $5|tr '[a-z]' '[A-Z]')
  mac6=$(echo $6|tr '[a-z]' '[A-Z]')
else
  usage
  exit 1
fi

# Ensure nothing

# Convert last three hexadecimal octets to decimal values
ip1=100
ip2=$(printf "%d" "0x$mac4")
ip3=$(printf "%d" "0x$mac5")
ip4=$(printf "%d" "0x$mac6")

normalize-ipv4-octet-2 $ip2
normalize-ipv4-octet-4 $ip4

echo "$ip1.$ip2.$ip3.$ip4"