#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;

my $start = '<START>';
my $end   = '<END>';

foreach (<DATA>) {
    chomp;
    print "$1\n" if /$start(.+)$end/;
}

__DATA__
<START>TEXT1<END>
<various data>
<START>TEXT2<END>
<various data>
<START>TEXT3<END>