Do a reverse lookup easily

reverse.sh

#  ⣏⡉ ⡀⢀ ⣀⡀ ⡇ ⢀⣀ ⣀⡀ ⢀⣀ ⣰⡀ ⠄ ⢀⡀ ⣀⡀
#  ⠧⠤ ⠜⠣ ⡧⠜ ⠣ ⠣⠼ ⠇⠸ ⠣⠼ ⠘⠤ ⠇ ⠣⠜ ⠇⠸
#
# Due to the complexity of parsing anothers output (and because everything 
# is different on other linux versions) I decided to revamp the code.
# 
# What's better:
# - multiple A record parsing (also with multiple PTR records now)
# - multiple PTR record parsing (now working w/o bugs)
# - better error handling based on empty result check
# - with the latest version many bugs are fixed now
# 
# 
#  ⡷⣸ ⢀⡀ ⡀ ⢀   ⣰⡁ ⡀⢀ ⣀⡀ ⢀⣀ ⣰⡀ ⠄ ⢀⡀ ⣀⡀
#  ⠇⠹ ⠣⠭ ⠱⠱⠃   ⢸  ⠣⠼ ⠇⠸ ⠣⠤ ⠘⠤ ⠇ ⠣⠜ ⠇⠸


# do a reverse lookup
# do a reverse lookup
reverse() {
	# put request in variable
	request="$1"

	# check for request
	if [ -z "$request" ]
	then
		echo "Please provide an IP or host name.".
		return
	fi
	
	# check for "dig" installed
	if [ -z "$(which dig)" ]
	then
		echo "Please install dig, we need it:"
		echo "sudo apt-get install dig (for Ubuntu/Debian)"
		return
	fi
	
	# decide if its an ip or name
	if [ "$(echo $request | egrep -o '[[:digit:]]{1,3}\.[[:digit:]]{1,3}\.[[:digit:]]{1,3}\.[[:digit:]]{1,3}')" ]
	then
		# would be an IP

		# for later check of any reverse
		check="false"

		# save/set IFS
		oldifs=$IFS
		IFS=$'\n'
		
		# loop through ptr records
		for r in $(dig +tcp +short -x $request 2> /dev/null)
		do
			# print ip address
			echo -n "$request"

			# print PTR
			echo " > $r"
			
			# set check to true due to at least one PTR
			check="true"
		done

		# set the old IFS
		export IFS=$oldifs

		# check if any ptr was found
		if [ $check == "false" ]
		then
			echo -ne "No reverse entry for $request.\n"
		fi
	else
		# would be a hostname

		# check if any output there
		if [ -z "$(dig a +search +short +tcp $request 2> /dev/null | egrep -o '[[:digit:]]{1,3}\.[[:digit:]]{1,3}\.[[:digit:]]{1,3}\.[[:digit:]]{1,3}')" ]
		then
			echo "No A records found for $request."
			return
		else
			# continue with a record(s)

			# save/set IFS
			oldifs=$IFS
			IFS=$'\n'

			# loop through A records
			for i in $(dig a +search +short +tcp $request 2> /dev/null | egrep -o '[[:digit:]]{1,3}\.[[:digit:]]{1,3}\.[[:digit:]]{1,3}\.[[:digit:]]{1,3}')
			do
				# for later check of any reverse
				check="false"

				# loop through ptr records
				for r in $(dig +tcp +short -x $i 2> /dev/null)
				do
					# print request and ip
					echo -n "$request > $i"

					# print PTR
					echo " > $r"
					
					# set check to true due to at least one PTR
					check="true"
				done

				# check if any ptr was found
				if [ $check == "false" ]
				then
					echo -ne "$request > $i > No reverse entry.\n"
				fi

			done

			# set the old IFS
			export IFS=$oldifs
		fi
	fi
}