opendir. If used in a list context, returns all the rest of
the entries in the directory. If there are no more entries, returns an
undefined value in a scalar context or a null list in a list context.
If you're planning to filetest the return values out of a
readdir, you'd better prepend the directory in question.
Otherwise, because we didn't chdir there, it would have been
testing the wrong file.
opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
@dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
closedir DIR;