It sounds as though you want to take random draws from a Normal distribution. I suspect that it's best to do this by calling R from Perl; that's how I did it. I don't have the code onhand, but I found almost all that I needed to know in the link from the previous sentence. (Also see this comment and Perl & Math: A Quick Reference. The relevant command in R is rnorm().)
As your needs grow -- e.g., if you start needing to take draws from different distributions, many of which are not written up in Perl modules -- it will help you more to be calling R from Perl.
Note that the probability of a draw from a continuous (e.g., Normal) distribution assuming any particular value is approximately zero.