Giant, thanks for all your help with this.

In the end I used a modification of mugwumpjism's suggestion to get to where I wanted to be.

Here's the code:

chdir "/home/www";
opendir DIR, ".";
my @vhosts=
    (
     # 1. This tests for the presence of directories
     grep { -d }
             (
              # 2. this returns all directories but . & ..
              grep { !/^\.\.?$/ && -d } (readdir DIR)
             )
    );

closedir DIR;
[download]

This sticks all my virtual hosts in an array :).