How to Generate Random Numbers in Perl

If you want to make random numbers in a given range, inclusive, such as when you randomly pick an array index, simulate rolling a die in a game of chance, or generate a random password, use Perl's rand function:

$random = int( rand( $Y-$X+1 ) ) + $X;

This code generates and prints a random integer between 25 and 75, inclusive:

$random = int( rand(51)) + 25;
print "$random\n";

The rand function returns a fractional number, from (and including) 0 up to (but not including) its argument. We give it an argument of 51 to get a number that can be 0 or more, but never 51 or more. We take the integer portion of this to get a number from 0 to 50, inclusive (50.99999.... will be turned
into 50 by int). We then add 25 to it to get a number from 25 to 75, inclusive.

A common application of this is the random selection of an element from an array:

$elt = $array[ rand @array ];

That's just like saying:

$elt = $array[ int( rand(0+@array) ) ];

Because rand is prototyped to take just one argument, it implicitly imposes scalar context on that argument, which, on a named array, is the number of elements in that array. The function then returns a floating-point number smaller than its argument and greater than or equal to zero. A floating-point number used as an array subscript implicitly undergoes integer truncation (rounding toward zero), producing in the end an evenly distributed, randomly selected array element to assign to $elt.

Generating a random password from a sequence of characters is similarly easy:

@chars = ( "A" .. "Z", "a" .. "z", 0 .. 9, qw(! @ $ % ^ & *) );
$password = join("", @chars[ map { rand @chars } ( 1 .. 8 ) ]);

We use map to generate eight random indices into @chars, extract the corresponding characters with a slice, and join them together to form the random password. This isn't a good random number, though, as its security relies on the choice of seed,
which (in older versions of Perl) is based on the time the program started.