All you need to do is:

use Env qw(PATH SYSTEMROOT); # or whatever...
[download]

All the info can be found here.

You could also use the built-in pseudohash %ENV like so:

perl -e"print $ENV{PATH}"
[download]

UPDATE: Some day I will snatch the pebble from Fastolfe's hand... ++ to him for beating me to it.