#!/usr/bin/perl

use v5.12;
use warnings;

sub readroot
{
	my $drive=shift;
	my $name="$drive:/";
	if (opendir my $d,$name) {
		my @list=grep /^\.{1,2}$/, readdir $d;
		closedir $d;
		return join(' ',"$drive:",@list);
	}
	return "$drive: $!";
}

say readroot($_) for ('A' .. 'Z');

##</code><code>##

X:\>subst
E:\: => C:\windows
F:\: => C:\

X:\>perl readdir.pl
A: No such file or directory
B: Invalid argument
C:
D:
E: . ..
F:
G: No such file or directory
H: . ..
I: . ..
J: No such file or directory
K: No such file or directory
L: No such file or directory
M: . ..
N: No such file or directory
O: No such file or directory
P: No such file or directory
Q: No such file or directory
R: . ..
S: No such file or directory
T: . ..
U:
V: . ..
W: No such file or directory
X:
Y: No such file or directory
Z: Invalid argument

X:\>