The original cause of the problem was not so much with "find", but rather with `cat $html_dir/$good_file` -- when running a shell command this way, cat will always tokenize the shell will always tokenize the output from cat (or other backtick command) on any whitespace, treating all whitespace the same (yielding a separate argument string) without paying any attention to any sort of escape mechanism (quotes, backslash, etc).

I don't want to discourage you from figuring out the proper way to use File::Find, but in my own experience, this module has normally been significantly slower in any task when compared to the standard "find" shell utility (and let's face it, File::Find's usage has a strange, counter-intuitive feel to it, which has tripped up a lot of folks).

Given your situation, that suddenly the list in "$html_dir/$good_file" happens to contain items with internal spaces, I would be inclined to figure out how to keep using the shell "find" approach -- e.g.:

open (LIST, "<$html_dir/$good_file");
my @paths = <LIST>;
close LIST;
chomp @paths;

my $total = 0;
for my $p (@paths) {
   my $count = qx/find "$p" -type d -name class | wc -l/;
   chomp $count;
   $total += $count;
}
[download]

Being able to put double quotes around the path argument in the find command line makes all the difference.

You might think you spend a lot of overhead running this many subshells with "qx//", but I wouldn't be surprised if this still ends up running faster than the equivalent File::Find solution (once you get that working -- good luck with that).

update: added "$total" to the code sample.