In addition to kyle's comment, you should note that ++$filename uses Perl magic to generate a sequence of file names. Unless you add a few digits to the end of the 'seed' file name the result may be other than you expect. Try running the following:

my $fn = 'xxx0';

print ++$fn, ' ' for 1 .. 11;
print "\n";

$fn = 'xx00';
print ++$fn, ' ' for 1 .. 11;
[download]