sub readin_dirs {
    my $dir = shift;
    my $DIR;
    # I use variable file handles so function can be reentrant
    opendir $DIR, $dir or die "opendir $dir - $!";
    my @entries = readdir $DIR;

    # Get only directories from dir listing.
    my @subdirs = grep { -d "$dir/$_" } @entries;

    # Remove "hidden" directories (including . and ..) from that list:
    @subdirs = grep { !/^\./ } @subdirs;

    for my $subdir ( @subdirs ) {
        now_do_something("$dir/$subdir");
    }
    closedir $DIR;
}
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