For Mac:

use strict;
use warnings;

my ($dir, $file, $path);
my ($script) = $0 =~ /([^:]+)$/;

my @dirs = ':';
while ($dir = shift(@dirs)) {
    opendir(DIR, $dir);
    while ($file = readdir(DIR)) {
        next if $file eq $script;
        $path = "$dir$file";
        if (-d $path) {
            push (@dirs, "$path:"); next;
        }
        #########
        # Open each $path and process
        #########
    }
}
[download]

Place in the main directory of the section you want processed.

EDIT: I could probably have simplified this, but it was a cut and paste from something I wrote back several years ago. Have fun.