use warnings;
use strict;

my $file = 'in.txt';
my ($start,$end);
open my $fh, '<:raw', $file or die "$file: $!";
my $offset = 0;
while (<$fh>) {
	$start = $offset if /PATTERN1/;
	$offset = tell $fh or die "tell: $!";
	$end = $offset if /PATTERN3/;
}
die "Failed to find second pattern after first pattern"
	unless defined $start && defined $end && $end > $start;
seek $fh, $start, 0 or die "seek: $!";
my $bytes = $end-$start;
read($fh, my $data, $bytes)==$bytes
	or die "failed to read $bytes bytes";
close $fh;
print $data;