open IN, '<', 'clients.txt' or die "Can't open file 'clients.txt': $!";
@clients = <IN>;
chomp @clients;

##</code><code>##

open IN, '<', 'subdirectories.txt' or die "Can't open file 'subdirectories.txt': $!";
@subdirs = <IN>;
chomp @subdirs;

##</code><code>##

my $year = 2005;
mkdir $year, 0755;
foreach my $client (@clients) {
    $client =~ /(\d*)\d/ or next; # we need digits;
    my $range = "${1}0_${1}9";
    -d "$year/$range" or mkdir "$year/$range", 0755
      or die "Can't create directory '$year/$range': $!";
    -d "$year/$range/$client" or mkdir "$year/$range/$client", 0755
      or die "Can't create directory '$year/$range/$client': $!";
    foreach my $subdir (@subdirs) {
        -d "$year/$range/$client/$subdir" or mkdir "$year/$range/$client/$subdir", 0755
          or die "Can't create directory '$year/$range/$client/$subdir': $!";
    }
}