my $iter = 0;
while( $iter++ < $MAX_ITERS ) {
  do_stuff();
}
##</code><code>##

{
   my $block_size = 207;
   sub get_block_size { $block_size }
}

##</code><code>##

sub nuke_file {
    my $file = shift;
    my $cb   = shift or die "No callback specified to nuke_file().\n";
    die "$cb is not a coderef in nuke_file()\n" unless ref($cb) eq 'CODE';

    my $file_size  = (stat($file))[7];
    my $bytes      = 0;
    my $block_size = get_block_size();

    sysopen(BYEBYE, $file, O_WRONLY)
        # be descriptive in your die string
        or die "Could not open $file for output: $!\n";

    while( $bytes < $file_size ) {
        # deal with the tail end of the file correctly
        my $len = $bytes + $block_size > $file_size
            ? $file_size - $bytes
            : $block_size;

        my $written = syswrite(BYEBYE, &$cb( $len ), $len, 0)
            or die "Could not write $len bytes to $file: $!";
        my $bytes += $written; # $err is a misleading name
    }
    close(BYEBYE);
}

##</code><code>##

sub all_ones {
    0xff x $_[0];
}

nuke_file( $filename, \&all_ones );