rand, srand

Fractional random numbers:

srand();                            # sets random seed, def.: time()
srand(1);                           # generate reproducible random number
srand( time() ^ ($$ + ($$ << 15))); # sets random seed, $$ is the PID  
$x = rand();                        # [0,1[
$x = rand(10);                      # [0,10[