Programming Perl, 4th Edition

rand

rand EXPR
rand

This function returns a pseudorandom floating-point number greater than or equal to 0 and less than the value of EXPR. (EXPR should be positive.) If EXPR is omitted, the function returns a floating-point number between 0 and 1 (including 0, but excluding 1). rand automatically calls srand unless srand has already been called. See also srand.

To get an integral value, such as for a die roll, combine this with int, as in:

$roll = int(rand 6) + 1;       # $roll now a number between 1 and 6

Because Perl uses your own C library’s pseudorandom number function, like random(3) or drand48(3), the quality of the distribution is not guaranteed. If you need stronger randomness, such as for cryptographic purposes, you might consult instead the documentation on random(4) if your system has a /dev/random or /dev/urandom device; the CPAN modules Math::Random::Secure, Math::Random::MT::Perl, and Math::TrulyRandom; or a good textbook on computational generation of pseudorandom numbers, such as the second volume of Knuth.^[247]

^[247] Knuth, D.E. The Art of Computer Programming, Seminumerical Algorithms, vol. 2, 3^rd ed. (Reading, Mass.: Addison–Wesley, 1997).