SortHostsFile

#!/bin/bash

if [ ! -f "$1" ]; then
	echo "File not found!"
	exit
fi

HOSTFILE=$1

function reverse {
	echo "$1" | awk '{ for(i=length;i!=0;i--)x=x substr($0,i,1);}END{print x}'
}

N=0
M=0
ARRAY=()
MAP_ARRAY=()
while read LINE ; do
	N=$((N+1))
	if ! echo $LINE | grep -E '(^[:space:]*#)|(^[:space:]*$)' > /dev/null; then
		arr=($LINE)
		if [[ ${#arr[@]} = 2 ]]; then
			M=$((M+1))
			ARRAY+=($(reverse "${arr[1]}"))
			MAP_ARRAY+=("${arr[1]}|${arr[0]}")
		elif [[ ${#arr[@]} > 2 ]]; then
			M=$((M+1))
			for (( i=1; i<${#arr[@]}; i++ )); do
			  ARRAY+=($(reverse "${arr[$i]}"))
			  MAP_ARRAY+=("${arr[$i]}|${arr[0]}")
			done
		fi
	fi
done < $HOSTFILE

ARRAY=($(printf '%s\n' "${ARRAY[@]}"|sort))
for domain in ${ARRAY[@]}; do
	rdomain=$(reverse "$domain")
	for item in ${MAP_ARRAY[@]}; do
		KEY=${item%%|*}
		VALUE=${item#*|}
		if [[ $rdomain == $KEY ]]; then
			echo "$VALUE $rdomain"
			break;
		fi
	done
done