That's easy. Generate as many as you want, all from 0 to 1. Then take their sum, and go back and multiply each element by 100 divided by that sum!

my @data;
push @data, rand 1 for 1..30; # for 30 numbers
my $sum;
$sum += $_ for @data; # calculate sum
$sum = 100 / $sum; # ratio to ensure they sum to 100
$_ *= $sum for @data; # then scale them all
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-- Randal L. Schwartz, Perl hacker