undef $/;
$_ = <>;
s/(\x31\x33\x39\x37[^\x00]*\x00)/"\x00" x length $1/ge;
print;

##</code><code>##

$/ = \4096;
my $flag = 0;
while (<>) {
    if ($flag) { # ended previous chunk in mid-substitution
        s/(^[^\x00]*(\z|\x00))/"\x00" x length $1/ge;
    }
    s/(1379[^\x00]*(\z|\x00))/"\x00" x length $1/ge;
    $flag =  length $2 ? 0 : 1; # this could be readily golfed, I realize
}