#!/bin/bash
IpAndNetmasktoNetwork()
{
  # expects $1 to be an ip address
  # expects $2 to be a netmask
  IP1="${1%.*.*.*}"
  IP2="${1%.*.*}"
  IP2="${IP2#*.}"
  IP3="${1%.*}"
  IP3="${IP3#*.*.}"
  IP4="${1#*.*.*.}"
  NM1="${2%.*.*.*}"
  NM2="${2%.*.*}"
  NM2="${NM2#*.}"
  NM3="${2%.*}"
  NM3="${NM3#*.*.}"
  NM4="${2#*.*.*.}"
  let "ipdec=$IP4 + (256*$IP3) + (256*256*$IP2) + (256*256*256*$IP1)"
  let "nmdec=$NM4 + (256*$NM3) + (256*256*$NM2) + (256*256*256*$NM1)"
  let "ipnet=$ipdec%$nmdec"
  count=0
  let "nmtemp=$nmdec"
  while [ $nmtemp -eq $nmdec ]
  do
    let "count+=1"
    let "nmtemp >>= $count+1"
    let "nmtemp <<= $count+1"
  done
  ipnet=$ipdec
  let "ipnet >>= $count"
  let "ipnet <<= $count"
  let "bits=32-$count"
  let "IPNET1=$ipnet/256/256/256"
  let "IPNET2=($ipnet-($IPNET1*256*256*256))/256/256"
  let "IPNET3=($ipnet-($IPNET1*256*256*256)-($IPNET2*256*256))/256"
  let "IPNET4=($ipnet-($IPNET1*256*256*256)-($IPNET2*256*256)-($IPNET3*256))"
  ipnet="$IPNET1.$IPNET2.$IPNET3.$IPNET4/$bits"
  echo $ipnet
}
INTIP="192.168.10.100"
INTMASK="255.255.255.0"
intnm="`IpAndNetmasktoNetwork "$INTIP" "$INTMASK"`"
echo $intnm