FAQ 4.10 Why aren't my random numbers random?

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4.10: Why aren't my random numbers random?

    If you're using a version of Perl before 5.004, you must call "srand"
    once at the start of your program to seed the random number generator.

             BEGIN { srand() if $] < 5.004 }

    5.004 and later automatically call "srand" at the beginning. Don't call
    "srand" more than once--you make your numbers less random, rather than

    Computers are good at being predictable and bad at being random (despite
    appearances caused by bugs in your programs :-). see the random article
    in the "Far More Than You Ever Wanted To Know" collection in
    http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz , courtesy of Tom Phoenix,
    talks more about this. John von Neumann said, "Anyone who attempts to
    generate random numbers by deterministic means is, of course, living in
    a state of sin."

    If you want numbers that are more random than "rand" with "srand"
    provides, you should also check out the "Math::TrulyRandom" module from
    CPAN. It uses the imperfections in your system's timer to generate
    random numbers, but this takes quite a while. If you want a better
    pseudorandom generator than comes with your operating system, look at
    "Numerical Recipes in C" at http://www.nr.com/ .


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