#!perl
use warnings;
use strict;
my $dir = '/home/sites/$arg1/users';
opendir DIR, $dir or die "Cannot opendir $dir:$!\n";
my @users = grep { -d  "$dir/$_" and not /^\.{1,2}$/} readdir DIR;
closedir DIR;

# do whatever you want with @users
print join "\n",@users;