In addition to Abigail's (as usual ;) correct assertion that Perl uses the OS' underpinnings to do (pseudo)random number generation, do note that as good as the PRNG is with drand48 (on most modern linux distributions), 48 bits is not sufficent for crypographic needs. For most computing purposes, it's sufficient - just not crypto. For that, there are several packages which work out a bit better - as have been mentioned earlier.
The problem doesn't stem from needing to draw 2G random numbers in a single run but how random the sequence is for those 2G numbers over multiple runs of smaller draws over time. Besides, to a human, 2G can seem like a big number but to a computer it's *teeny*.
As an introduction into the visualization of PRNG data, I'd recommend having a look at this
where they've analyzed the pseudorandomness in the TCP sequences of various stack implimentations.