addondomain details API

I want to write a script in perl that runs in the server such that whenever a
user create a new addon domain or subdomain from his cpanel I should be able to write it to a file with the following details.

subdomain name
addon domain name
user who created the addon domain
document root of the new addon domain

Please point out the easiest way by which I can pass the variables to my perl
script.

I searched for API and found

<?cp AddonDomain::addaddondomain('% %',result,reason) newdomain=$FORM{'domain'},dir=$FORM{'dir'},subdomain=$FORM{'user'},pass=$FORM{'pass'} ?>

and how can I make use or the details from the FORM to pass into my scripts variables.

I find this is commented in x3 theme but when I have deleted this code from doaddondomain.html addon domain is not getting created. So somehow this function is called by cpanel while adding addondomains.

Any help would be greatly appreciated.

 

Thanks Matt and David for your assistance, hooks did the trick for me.