#!/usr/bin/bash

CIDR=192.168.0
STARTOCTET=0
ENDOCTET=1

while getopts O:o: flag
do
    case "${flag}" in
        O) filename=${OPTARG};;
        o) filename=${OPTARG};;
    esac
done

echo "Please enter the starting octet..."
read STARTOCTET

echo "Please enter the ending octet..."
read ENDOCTET

[ -n "$STARTOCTET" ] && [ "$STARTOCTET" -eq "$STARTOCTET" ] 2>/dev/null
if [ $? -ne 0 ]; then
   echo $STARTOCTET is not number
   exit 1
fi

[ -n "$ENDOCTET" ] && [ "$ENDOCTET" -eq "$ENDOCTET" ] 2>/dev/null
if [ $? -ne 0 ]; then
   echo $ENDOCTET is not number
   exit 1
fi

if (( $ENDOCTET < $STARTOCTET)); 
then
	echo "Start octect must be earlier than ending octet"
	exit 1
fi

for i in $(seq $STARTOCTET $ENDOCTET)
do
	echo "scanning $i"
	nmap -Pn -F $CIDR.$i >> $filename
done