#!/usr/bin/perl

use strict;
use warnings;

while($_=<DATA>){
        if (/^\[Note\]\w+,(\w+)/){
                my $x =$1;
                print "$x\n";
        }

}

__DATA__
[Note]note_values,notes_values2
[Book]novels,magazines
[download]

A couple of comments:

• use strict and use warnings even on a little script they will often catch a simple error that your eyes will gloss over "seeing what I meant to write"
• $x=~/^\[Note\](\w+)/; tries to match the regex in $x
• I think it does what you're looking for, if I read your question correctly