Convert IP address string to integer

ip_to_int.sh

#!/bin/sh
function ip_to_int() {
  local -ai M=(16777216 65536 256 1)
  local -i  INT=0
  local     OIFS=${IFS}
  IFS="."
  set -- ${*}
  for I in {1..4}
  do
    let INT+=$[${!I}*${M[I-1]}]
  done
  IFS=${OIFS}
  echo "${INT}"
  return 0
}
function int_to_ip() {
  local -a IP=($[${1}/16777216] $[${1}%16777216/65536] $[${1}%65536/256] $[${1}%256])
  echo "${IP[0]}.${IP[1]}.${IP[2]}.${IP[3]}"
  return 0
}
if [[ ${1} =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]]
then
  ip="${1}"
  echo -e "IP address\t\t= ${ip}"
  int=$( ip_to_int ${ip} )
  echo -e "integer\t\t\t= ${int}"
  if hash rax2
  then
    nbo=$( rax2 -e ${int} )
    echo -e "network byte order\t= ${nbo}"
  fi
else
  echo "IP address?" 1>&2
  exit 1
fi
exit 0