DevTut

# Randomness

# Accessing an array element at random

my @letters = ( 'a' .. 'z' );                # English ascii-bet

print $letters[ rand @letters ] for 1 .. 5;  # prints 5 letters at random

How it works

  • rand EXPR (opens new window) expects a scalar value, so @letters is evaluated in scalar context
  • An array in scalar context returns the number of elements it contains (26 in this case)
  • rand 26 returns a random fractional number in the interval 0 ≤ VALUE < 26. (It can never be 26)
  • Array indices are always integers, so $letters[rand @letters] ≡ $letters[int rand @letters]
  • Perl arrays are zero-indexed, so $array[rand @array] returns $array[0], $array[$#array] or an element in between

(The same principle applies to hashes)

my %colors = ( red   => 0xFF0000,
               green => 0x00FF00,
               blue  => 0x0000FF,
             );

print ( values %colors )[rand keys %colors];

# Generate a random integer between 0 and 9

Cast your random floating-point number as an int.

Input:

my $range = 10;

# create random integer as low as 0 and as high as 9
my $random = int(rand($range));   # max value is up to but not equal to $range

print $random . "\n";

Output:

A random integer, like...

0

See also the perldoc for rand (opens new window).

# Generate a random number between 0 and 100

Pass an upper limit as an argument to the rand() function.

Input:

my $upper_limit = 100;
my $random = rand($upper_limit);

print $random . "\n";

Output:

A random floating-point number, like...

45.8733038119139

# Remarks

Documentation for perl's rand() function: http://perldoc.perl.org/functions/rand.html (opens new window)

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