opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
my @files = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
closedir(DIR);
@files = sort {$a <=> $b} @files; # Ascending sort

my $count = 1;
foreach (@files) {
   rename($_, "testfile$count") or warn "rename: $_ : $!";
   $count = $count + 1;
}