how can you generate unique random numbers in perl?

Barry Kaplan

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Jan 31, 1998, 3:00:00 AM1/31/98

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Bob Trieger

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Jan 31, 1998, 3:00:00 AM1/31/98

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Barry Kaplan wrote:
:
: how can you generate unique random numbers in perl?

go to http://www.perl.com/ it is in the FAQs there.

HTH
Bob Trieger
co...@ma.ultranet.com

Hank LeMieux

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Feb 1, 1998, 3:00:00 AM2/1/98

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Howdy Barry,

Barry Kaplan wrote:
:
: how can you generate unique random numbers in perl?

Well, I just happen to have recently written a subroutine for just that
purpose!

One key thing to remember as you go over this is that perl cannot
generate a truly random number. It needs some help from you. If you
ask it to randomize and you do that over a long enough period, it will
begin to repeat itself at some point. Many people therefore interject
the time as a randomization modifier, as I have done here, since the
time continually changes. This should not be done, however, if you're
using this to control secure access or the like, as the time, of course,
is predictable.

Here's the routine. You call it as follows:

$yourRandomNumber = &randomNumber($a,$b,$c) ;

Where $a and $b are upper and lower limits for your random number and $c
equals 'whole' if you want a whole number back or 'integer' else if you
want an integer back.

sub randomNumber
{
my ($lowerLimit,$upperLimit,$type) = @_ ; # import passed variables
my $range = ($upperLimit - $lowerLimit) ; # set range to randomize
across

srand(time()); # use time as the
randomization factor
my $randomFactor = rand($range) ; # generate random number
my $output = ($lowerLimit + $randomFactor) ; # add to lower limit to
reach output

if ( $type = "whole" ) # if whole number wanted,
clip off
{ # decimals
$output =~ /^(\d+)\./o ;
}

return ($output) ; # return output
}

Good luck!

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David Richards

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Feb 1, 1998, 3:00:00 AM2/1/98

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In article <34D3C8EB...@ibm.net>, Hank LeMieux <han...@ibm.net> wrote:
:Howdy Barry,
.

:Barry Kaplan wrote:
:: how can you generate unique random numbers in perl?

.
:Well, I just happen to have recently written a subroutine for just that
:purpose!

Please note that if your routine is used in a CGI script, and two different
requests come in during the same second, they will both get the same
number assigned (because you use 'srand(time())' to 'seed' rand).

I posted a possible solution here (for CGI scripts) a week or so ago.

:One key thing to remember as you go over this is that perl cannot

:generate a truly random number. It needs some help from you. If you
:ask it to randomize and you do that over a long enough period, it will
:begin to repeat itself at some point. Many people therefore interject
:the time as a randomization modifier, as I have done here, since the
:time continually changes. This should not be done, however, if you're
:using this to control secure access or the like, as the time, of course,
:is predictable.

Using the time by itself only works if you also can ensure that you won't
have two requests within the span of a single second. This could be caused
by the same person running the script twice really quickly, or two
different people using the script at the exact same moment.

The time continually changes, but on some scales a second is a LONG time :-)

..
:Here's the routine. You call it as follows:
..
: srand(time()); # use time as the randomization factor

: my $randomFactor = rand($range) ; # generate random number