#!/usr/bin/perl -w
use strict;
use warnings;
while(<DATA>){
        if (/<STANDARD>.*/) {
                print;
        }
        if (/>JN.*/) {
                print;
        }
}
__DATA__
<DIVIDER>file.txt</DIVIDER>
<STANDARD>....
....
...

<DIVIDER>file.txt</DIVIDER>
>JN....