my $dir  = shift || "client";
my @list = ();

for( glob "*$dir*" ){
    -d or next;
    for( glob "$_/*" ){
        -d or next;
        push @list, $_;
    }
}

$" = $/;

print "@list"

__END__
client1/DIR_1
client1/DIR_2
client1/DIR_3
client2/DIR_1
client2/DIR_2
client2/DIR_3
client3/DIR_1
client3/DIR_2
client3/DIR_3