Heh. Funny just today I used this property to my advantage:

    my $filter = @$custs ? join('|', map quotemeta($_),@$custs) : "";
    $filter=qr/^(?!_)(?:$filter)/i;

    ( my $year_mon = $mon_year ) =~ s/(\d+)_(\d+)/20${2}_${1}/;

    my @dirs = map {
        if (-d $_) {
            warn "Considering: $_\n";
            s/.*?([^\\\/]+)$/$1/;
            if (/$filter/) {
                warn "Processing: $_\n";
                $_
            } else {
                warn "Skipping: $_\n";
                ()
            }
        } else {
            ();
        }
    } glob File::Spec->catfile( $root, '*' );
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This code scans a directory and either includes all directories that dont begin with an _ or only the customers specified in the @$custs array (that dont start with _). I just thought it was funny reading this only minutes after I wrote the above code. (Actually modified some ugly old code to handle a customer filter. Obviously I didnt bother de-uglifying it ;-)

Anyways, just thought i'd share the irony with yall.