Randomness In Perl

Rand Basics

The rand function returns a decimal number between 0, including 0, and the inputed number, not inclusive. Therefore, rand(7) would return a decimal between 0 and 7. If there is no input, then rand would return a number between 0 and 1.

But I Want A Number Between 0 And 50.

print int rand 51;

Perl’s rand() function isn’t built to give you integers. However, with the int() function you can make it do your bidding. However, it’s important to notice that you have to enter a number one greater than the largest number you’re looking for.

Rand And Arrays

my @array = ( ‘first possibility’,'second’,'third’);

print $array[int rand scalar @array];

This code works with almost any input as @array. URLs, images, possible passwords, whatever you need can be in @array. The function is returning the int rand result of the scalar value of @array. What’s important to note is that with arrays, the scalar value is one higher than the highest key value of @array (Perl’s arrays are indexed at 0).

Truly Random

Use of Perl’s rand() function is not advised for cryptographers. The rand() function uses a seed to generate its input, and unfortunately that seed is predictable approximately one third of the time. Check out perldoc -f srand and perldoc -f rand for more information on this. Instead, it’s advised that for truly random input, one should use the Perl Module Math::TrulyRandom.