#!/bin/sh

#################################################
## rdns v2.22                                  ##
## this script takes an IP address (or the     ##
## first three octets of an IP address) and    ##
## looks up all of names associated with the   ##
## IP addresses within that class C network.   ##
##                                             ##
## more info:                                  ##
## http://Business-PHP.com/opensource/rdns/    ##
##                                             ##
## Copyright (C) 16 Feb 2003 Atom Emet         ##
## Atom*Business-PHP.com                       ##
##                                             ##
## This program is free software; you can      ##
## redistribute it and/or modify it under the  ##
## terms of the GNU General Public License as  ##
## published by the Free Software Foundation;  ##
## either version 2 of the License, or         ##
## (at your option) any later version.         ##
##                                             ##
## This program is distributed in the hope     ##
## that it will be useful, but WITHOUT ANY     ##
## WARRANTY; without even the implied warranty ##
## of MERCHANTABILITY or FITNESS FOR A         ##
## PARTICULAR PURPOSE. See the GNU General     ##
## Public License for more details.            ##
##                                             ##
## You should have received a copy of the      ##
## GNU General Public License along with this  ##
## program; if not, write to                   ##
##    the Free Software Foundation, Inc.       ##
##    59 Temple Place - Suite 330              ##
##    Boston, MA  02111-1307, USA              ##
#################################################

#################################################
## check if the input appears to be an IP address
## or the first 3 octets of an IP address
##
ip_test1=`echo "${1}" | tr '.' ' '`
ip_test2=`echo "${1}" | egrep '^[0-9.][0-9.]*$'`
ip_test3=`echo "${1}" | tr '.' ' ' | wc -w`
#########################################################
## the "1" in the following line will cause the following
## tests to be made even if there is no input
##
## although there is some redundancy in the following
## loop, it should not add any significant run time
##
for x in ${ip_test1} 1
do
        if [ ! "${ip_test2}" ] || [ "${x}" -gt 255 ] || [ "${ip_test3}" -gt 4 ] || [ "${ip_test3}" -lt 3 ]
        then
	    ####################################################
	    ## if the argument doesn't seem to be an IP address,
            ## or is missing - issue an error and bail out
	    ##
	    echo "Usage: rdns [IP-Address]" >&2
	    exit 1
        fi
done


#################################################################
## we're only concerned with the first 3 octets of the IP address
##
first_three_octets=`echo "${1}" | cut -d. -f1-3`

##################################################################################
## some systems have `jot`, other systems have `seq`
## few systems have both, so this function does their job and counts from 0 to 255
##
count () {
    n=0
    while [ "${n}" -lt '256' ]
    do
	echo "${n}"
	n=`expr "${n}" + 1`
    done
}

######################################################################
## this is the fun part
## append a sequential number from the `count` function to
## the first three octets of the IP address and lookup each IP address
## 
for fourth_octet in `count`
do
    ########################
    ## lookup the IP address
    ##
    name=`host -t a "${first_three_octets}.${fourth_octet}" 2> /dev/null`
    ###############################################
    ## we'll check the exit status a few lines down
    ##
    name_err="$?"
    ##################################################
    ## get the name(s) associated with that IP address
    ##
    name=`echo "${name}" | cut -d' ' -f5-`
    ######################################################
    ## did we successfully find a name for the IP address?
    ##
    if [ "${name_err}" = '0' ] && [ "${name}" ] && [ "${name}" != 'for' ]
    then
	if [ "${newline}" ]
	then
	    ##################################################################################
	    ## generate a line-feed *IF* this successful lookup follows an unsuccessful lookup
	    ##
	    echo ''
	fi
	########################################
	## echo the IP address we just looked up
	## followed by a literal tab
	## and gobble up the newline
	##
	echo "${first_three_octets}.${fourth_octet}	" | tr -d '[\n\r]'
	###########################################################
	## echo the name(s) associated with the IP
	## this is echoed on the same line as the IP, after the tab
	##
	echo ${name} | sed 's!^for !!'
	###############################
	## unset the "newline" variable
	##
	newline=
    else
	###########################################################
	## if we didn't successfully find a name for the IP address
	## echo a '*' and gobble up the newline
	##
	echo '*' | tr -d '[\n\r]'
	#############################
	## set the "newline" variable
	##
	newline=1
    fi
done

##################################################
## at this point, we've looked up 256 IP addresses
## it's almost quittin' time
##

if [ "${newline}" ]
then
    ###################################################################################
    ## if the last IP wasn't successfully looked up, enter a line-return before exiting
    ##
    echo ''
fi