#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;


my $file = 'textfile.txt';
open my $fh, '<', $file or die;
$/ = undef;
my $text = <$fh>;
close $fh;

my %res = $text =~ /BEGIN_TAG_(\d+)(.*?)END_TAG/sg;

print Dumper (\%res);