Random provides an interface to Ruby's pseudo-random number generator, or PRNG. The PRNG produces a deterministic sequence of bits which approximate true randomness. The sequence may be represented by integers, floats, or binary strings.
The generator may be initialized with either a system-generated or user-supplied seed value by using
Random.new will create a new PRNG with a state independent of
Random::DEFAULT, allowing multiple generators with different seed values or sequence positions to exist simultaneously.
Random objects can be marshaled, allowing sequences to be saved and resumed.
PRNGs are currently implemented as a modified Mersenne Twister with a period of 2**19937-1.
Returns true if the two generators have the same internal state, otherwise false. Equivalent generators will return the same sequence of pseudo-random numbers. Two generators will generally have the same state only if they were initialized with the same seed
Random.new == Random.new # => false Random.new(1234) == Random.new(1234) # => true
and have the same invocation history.
prng1 = Random.new(1234) prng2 = Random.new(1234) prng1 == prng2 # => true prng1.rand # => 0.1915194503788923 prng1 == prng2 # => false prng2.rand # => 0.1915194503788923 prng1 == prng2 # => true
Returns a random binary string containing
random_string = Random.new.bytes(10) # => "\xD7:R\xAB?\x83\xCE\xFAkO" random_string.size # => 10
Returns an arbitrary seed value. This is used by
Random.new when no seed value is specified as an argument.
Random.new_seed #=> 115032730400174366788466674494640623225
prng = Random.new prng.rand(100) # => 42
max is a
rand returns a random floating point number between 0.0 and
max, including 0.0 and excluding
prng.rand(1.5) # => 1.4600282860034115
max is a
rand returns a random number where range.member?(number) == true.
prng.rand(5..9) # => one of [5, 6, 7, 8, 9] prng.rand(5...9) # => one of [5, 6, 7, 8] prng.rand(5.0..9.0) # => between 5.0 and 9.0, including 9.0 prng.rand(5.0...9.0) # => between 5.0 and 9.0, excluding 9.0
Both the beginning and ending values of the range must respond to subtract (
-) and add (
+)methods, or rand will raise an
Returns the seed value used to initialize the generator. This may be used to initialize another generator with the same state at a later time, causing it to produce the same sequence of numbers.
prng1 = Random.new(1234) prng1.seed #=> 1234 prng1.rand(100) #=> 47 prng2 = Random.new(prng1.seed) prng2.rand(100) #=> 47
Seeds the system pseudo-random number generator,
number. The previous seed value is returned.
number is omitted, seeds the generator using a source of entropy provided by the operating system, if available (/dev/urandom on Unix systems or the RSA cryptographic provider on Windows), which is then combined with the time, the process id, and a sequence number.
srand may be used to ensure repeatable sequences of pseudo-random numbers between different runs of the program. By setting the seed to a known value, programs can be made deterministic during testing.
srand 1234 # => 268519324636777531569100071560086917274 [ rand, rand ] # => [0.1915194503788923, 0.6221087710398319] [ rand(10), rand(1000) ] # => [4, 664] srand 1234 # => 1234 [ rand, rand ] # => [0.1915194503788923, 0.6221087710398319]
Returns a string, using platform providing features. Returned value is expected to be a cryptographically secure pseudo-random number in binary form. This method raises a
RuntimeError if the feature provided by platform failed to prepare the result.
In 2017, Linux manpage random(7) writes that “no cryptographic primitive available today can hope to promise more than 256 bits of security”. So it might be questionable to pass size > 32 to this method.
Random.urandom(8) #=> "\x78\x41\xBA\xAF\x7D\xEA\xD8\xEA"