Palindrome Check

#!/bin/bash
echo -n "Enter a String: "
read str
n=${#str}               #n denotes number of characters in the string

for(( i=$n-1; i>=0; i-- ))      #loop for reversing str
do
    rev_str+=${str:$i:1}        #substring of length 1 from str(char no. i) added to rev_str
done

echo "Is "$str" and "$rev_str" the same?"
#echo "The String in reverse is "$rev_str

if [ "$str" == "$rev_str" ]; then
    echo "YES. So, it's a Palindrome."
else echo "NO. So, it's not a Palindrome."
fi