#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;

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

my $data = do {
    local $/;
    <DATA>;
};

while ($data =~ /\Q$start\E(.+?)\Q$end\E/sg) {
    print "$1\n";
}

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