If we have two commands, it might be better to first find the command to run, and then call it, rather than using a short circuit operator to extend support for this. Perhaps something like this?

```ruby
xen_commands = ['/usr/sbin/xl', '/usr/sbin/xm']
command = xen_commands.find { |cmd| Facter::Util::Resolution.which(cmd) }
if command
  if xm_list = Facter::Util::Resolution.exec("#{cmd} list 2>/dev/null")
  # ...
```

What do you think of this approach?