to answer your question, if you want to grab the ip of a user, look at $ENV{'REMOTE_ADDR'}. I'll take it a step further, if you want to change that IP into an address (or if $ENV{'REMOTE_HOST'} doesn't exist), try this:

$ip = $ENV{'REMOTE_ADDR'};
@digits = split (/\./, $ip);
$address = pack ("C4", @digits);
$host = gethostbyaddr ($address, 2);
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other environmental variables you might find useful:

$ENV{'HTTP_REFERER'} will contain where the user came from (a url)

$ENV{'HTTP_USER_AGENT'} contains browser information of the user

$ENV{'REQUEST_METHOD'} contains the request method (post, get) $ENV{'QUERY_STRING'} is what the query string was, everything after the '?' in the url