#!/bin/bash
#Filename: match_palindrome.sh
#Description: Find out palindrome strings from a given file

if [ $# -ne 2 ];
then
	echo "Usage: $0 filename string_length"
	exit -1
fi

filename=$1 ;

basepattern='/^\(.\)'

count=$(( $2 / 2 ))

for((i=1;i<$count;i++))
do
	basepattern=$basepattern'\(.\)' ;
done

if [ $(( $2 % 2 )) -ne 0 ];
then
	basepattern=$basepattern'.' ;
fi


for((count;count>0;count--))
do
	basepattern=$basepattern'\'"$count" ;
done

basepattern=$basepattern'$/p'
sed -n "$basepattern" $filename