Shortest code to produce non-deterministic output

Question

You need to produce output that is non-deterministic.

In this case, this will be defined to mean that the output will not always be the same result.

Rules:

• A pseudo-random number generator that always has the same seed does not count.

• You can rely on the program being run at a different (unknown) time each execution.

• Your code's process id (if it's not fixed by the interpreter) can be assumed to be non-deterministic.

• You may rely on web-based randomness.

• Your code may not take non-empty input. Related meta post.

• The program is not required to halt, but the output must be displayed.

Leaderboard

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Answer 1

WinDbg, 1 byte

#

Wow! Never expected a 1 byte solution from WinDbg!

# searches for a disassembly pattern, but since there's no parameters, it looks to just return the next assembly instruction in whatever dump/process you're attached to. Not sure the logic for setting the initial address, but it does.

Sample output:

0:000> #
Search address set to 75959556 
user32!NtUserGetMessage+0xc
75959556 c21000          ret     10h

0:000> #
user32!NtUserGetMessage+0xf 
75959559 90              nop

0:000> #
user32!NtUserMessageCall 
7595955a 90              nop

0:000> #
user32!NtUserMessageCall+0x1 
7595955b 90              nop

0:000> #
user32!NtUserMessageCall+0x2 
7595955c 90              nop

0:000> #
user32!NtUserMessageCall+0x3 
7595955d 90              nop

0:000> #
user32!GetMessageW
7595955e 8bff            mov     edi,edi

0:000> #
user32!GetMessageW+0x2 
75959560 55              push    ebp

0:000> #
user32!GetMessageW+0x3 
75959561 8bec            mov     ebp,esp

0:000> #
user32!GetMessageW+0x5 
75959563 8b5510          mov     edx,dword ptr [ebp+10h]

Answer 2

MATLAB, 3 bytes

why

why provides answers to almost any question. A few examples:

why
The programmer suggested it.

why
To fool the tall good and smart system manager. 

why
You insisted on it.

why
How should I know?

This is shorter than any rand function I can think of.

Answer 3

Java 7, 33 30 27 bytes

int a(){return hashCode();}

Because Java.

Answer 4

huh?, 0 bytes

An empty program still produces output. The last lines of the Python interpreter that are executed:

print "..."
f = open('Notes.txt', 'w')
f.write(time.strftime("%c") + " - The user tried to give me commands again. I still have no idea what they are talking about...\n")

At the end of a program, the Python interpreter will print ..., then it will create/open a text file called Notes.txt and write a string which contains the current time in front.

Answer 5

R, 1 byte

t

Outputs the function's source code and a memory pointer address which changes with every (re-)start of R.

Answer 6

Minecraft, 5 4 bytes

op 8

Used by typing into a server's console or a command block and giving it power. Can be run from the chat interface by prepending a /.

Usually this does nothing, but if there's a player with the username "8" on the server, they will be given operator permissions. Note that while Minecraft normally requires usernames to be 3 characters long, some accounts with shorter name lengths were created before this restriction.

The version that can be demonstrated to be non-deterministic without one of these usernames or risk of giving a user operator permissions is here:

me @r

Displays a message to everyone, the message being the username of a random player. The op command only takes a string literal, not any script that returns a string.

The me command wouldn't really work for the first example, it would display "<your-username> 8". When run from a command block, it wouldn't be deterministic since all command blocks have the same "username" but running it from the chat interface would require the / for one extra byte.

Answer 7

Labyrinth, 5 bytes

v
!
@

Either prints 0 or nothing (50% chance each).

Try it online!

There is a very specific case in which Labyrinth exhibits random behaviour:

• There must be a wall in front of the instruction pointer and behind it.
• There must be a non-wall left and right of the instruction pointer.
• The current top of the stack must be zero.

If all of those conditions are met, the direction the IP moves in is chosen (uniformly) randomly. The cherry on top is that those three conditions are impossible to meet in regular control flow, which means unless you modify the source code at runtime.

(This may seem a bit arbitrary, but it's actually the most consistent behaviour I could find for these conditions, since normally the direction of the IP always depends on the previous direction, its neighbours, and the sign of the top of the stack, and this seemed like an elegant way to include a source of randomness in the language.)

With the help of the source code rotation instructions (<^>v) it's possible to bring the IP into this situation. One such example is seen at the top. The IP initially points east and starts at the top. The v rotates the current column so that we get:

@
v
!

The IP moves along with this rotation so that it's still on the v, pointing east. All the conditions are fulfilled now, so the IP will either go up or down randomly. If it goes up, the program terminates immediately. If it goes down, it prints a zero, rotates the column again, and then terminates.

There are three other programs making use of this (one which also prints 0, one which prints 00 and one which prints 000):

v
@
!

"
>@!

"
>!@

(Actually there are a lot more than three other programs, because you could also use . instead of ! to print null bytes, or replace that " with a large variety of commands, but I believe they all work essentially the same.)

Answer 8

Befunge (-93 and -98), 3 bytes

?.@

The ? sends execution in a random direction. If it goes up or down, it loops back to the ? and rerolls. If it goes left, the program wraps round to the @ and thus exits without printing anything. If it goes right, it prints 0 (the output produced by . when the stack is empty) and then exits on the @.

Answer 9

sh + procps, 1 byte

w

This is the shortest solution I'm aware of that works via calling into external executables. procps is the responsible package for reporting information about the current system state (ps and friends), and is installed on most Linux distributions by default; w is the shortest-named command in it, and returns information about the logged-in users, but also some nondeterministic information like uptime.

Answer 10

Inform 7, 6 bytes

x is y

This isn't a valid Inform 7 program, since neither "x" nor "y" has been defined. So this throws an error.

However, some of Inform 7's error messages—including this one—are randomized. So the text it prints is technically non-deterministic.

A few possible outputs include:

Problem. The sentence 'x is y' appears to say two things are the same - I am reading 'x' and 'y' as two different things, and therefore it makes no sense to say that one is the other: it would be like saying that 'Adams is Jefferson'. It would be all right if the second thing were the name of a kind, perhaps with properties: for instance 'Virginia is a lighted room' says that something called Virginia exists and that it is a 'room', which is a kind I know about, combined with a property called 'lighted' which I also know about.

Problem. The sentence 'x is y' appears to say two things are the same - I am reading 'x' and 'y' as two different things, and therefore it makes no sense to say that one is the other: it would be like saying that 'Adam is Eve'. It would be all right if the second thing were the name of a kind, perhaps with properties: for instance 'Land of Nod is a lighted room' says that something called Land of Nod exists and that it is a 'room', which is a kind I know about, combined with a property called 'lighted' which I also know about.

Problem. The sentence 'x is y' appears to say two things are the same - I am reading 'x' and 'y' as two different things, and therefore it makes no sense to say that one is the other: it would be like saying that 'Clark Kent is Lex Luthor'. It would be all right if the second thing were the name of a kind, perhaps with properties: for instance 'Metropolis is a lighted room' says that something called Metropolis exists and that it is a 'room', which is a kind I know about, combined with a property called 'lighted' which I also know about.

Problem. The sentence 'x is y' appears to say two things are the same - I am reading 'x' and 'y' as two different things, and therefore it makes no sense to say that one is the other: it would be like saying that 'Aeschylus is Euripides'. It would be all right if the second thing were the name of a kind, perhaps with properties: for instance 'Underworld is a lighted room' says that something called Underworld exists and that it is a 'room', which is a kind I know about, combined with a property called 'lighted' which I also know about.

Answer 11

JavaScript, 4 bytes

Date

A function which returns the current date/time. I think this is the shortest it will get...

Explanation

Since this seems to be causing a lot of confusion as to why it's valid, I'll try to explain.

In JavaScript, a function entry is valid if it can be assigned to a variable and called like a function. For example, this function is a valid entry:

function(){return Date()}

Because it is a function that can be assigned to a variable like so:

f=function(){return Date()}

And then run with f() as many times as necessary. Each time, it returns the current date/time string, which has been ruled non-deterministic by the OP.

This ES6 arrow function is also valid:

_=>Date()

It can be assigned with f=_=>Date(), then run with f() like the other one.

Now, here's another valid entry:

Date

Why? Because just like the other two entries, it can be assigned with f=Date and then called with f(), returning exactly the same thing as the other two. Try it:

var f = Date

<button onclick="console.log(f())">Run</button>

Answer 12

Haskell, 49 bytes

import Unsafe.Coerce
main=putStr[unsafeCoerce(+)]

Unfortunately this seems to always outputs the same thing on TIO (I don't quite know why, but I have some guesses), so if you want to try it you should run it locally.

I've only tested this on Linux and OSX. I make no guarentees about Windows. If you are having trouble getting it to work on Linux I would be interested to know.

Explanation

What is unsafeCoerce?

This answer relies on unsafeCoerce. This function is a bit of magic, so first we are going to have to do a quick intro to Haskell's type system.

Haskell has something called type erasure. This means that the compiler checks all the types to make sure that nothing in the program is called on the wrong type. Once it is done with that there is no need to actually store type information any more, so Haskell erases it. So at runtime all data is the same and just relies on the fact that we already checked all the types before hand so nothing goes horribly wrong.

unsafeCoerce is a function that lies to the type checker. It tells it that it can take any input and produce any output; it's type is

forall a. forall b. a -> b

But it does nothing, it gives back the input exactly as it got it. So if you take a string like "abcd" and coerce it to an int using unsafeCoerce the result will be whatever the representation of "abcd" in memory is when interpreted as an integer.

How are functions represented in memory?

In Haskell, all complex objects including functions are internally represented as a pointer. This is a number in binary that "points" to a specific location in memory. This is because we want to pass these values by reference, since copying the whole thing is expensive, and since Haskell disallows mutation we can with no problem.

However simple objects like ints are passed by value since they are so small that copying them is about as expensive as copying a pointer would be. So they are not represented as pointers but rather just whatever structure they are.

So if we use unsafeCoerce from a complex object, say a function, to a simple object, say an Int, what happens is that the pointer to the function gets converted to the simple object. And the value of that simple object is dependent only on where the complex object is located not anything about what it is.

Address Space Layout Randomization

More reading

Many software vulnerabilities rely in part on being able to find particular functions in computer memory to access them. For these techniques you create some malicious code somewhere in memory (this can be done a few ways) and then by hijacking the stack pointer convince a program to run your code. In order to combat these exploits many systems implement something called Address Space Layout Randomization or ASLR. With ASLR key components are placed randomly so that their locations cannot be predicted. This means even if you do get control of the stack pointer it is hard to find where your malicious code is placed. ALSR is not the only technique used against these attacks but it is one we care about.

For Linux systems you can check of ASLR is on using

cat /proc/sys/kernel/randomize_va_space

Or since this is code-golf:

sysctl -anr "e_v"

There are three levels of security here 0 for off, and 1 and 2 for varying levels of on. My computer has this set to 2 (and your computer probably does too).

You can also set this. However do not do this unless you know what you are doing. Please do not mess with your kernel (unless you know what you are doing). For this reason I'm not going to include the command to do this, but you can look it up online or figure it out from the commands I already gave.

What this means for us is that the locations for objects allocated by Haskell at runtime is random or at least non-deterministic. This means that when we take a complex object like a function and convert it to a simple object like an Int the value of that object is random too.

The program

So that's what our program does. We coerce a function, (+) because it is short. We wrap this in a list and print it using putStr. Since putStr expects a string the compiler infers that the output of unsafeCoerce(+) must be a Char, which is a simple type.

So we end up printing a random one character string.

A more normal solution, 44 bytes

import System.Random
main=randomIO>>=putChar

Try it online!

For completion sake this is the "normal" Haskell approach. It is slightly shorter but far more boring.

Answer 13

Pyth, 2 bytes

O0

Explanation:

 0 0
O  Random float in [0, 1)

It's that, when O has 0 as its argument, it simply returns a random float between 0 and 1, exclusive.

Let's do it just for the heck of it!

Also, it seems that this can be sorta retro (thanks to 34718/mbomb007):

---

Pyth, 2 bytes

OT

Explanation:

 T 10
O  Random integer in [0, 10]

Try this boooooooooooooooring version instead >:(

Answer 14

Python 2, 11 bytes

print id(1)

Answer 15

Bash (procps-ng), 2 bytes

ps

$$ is also a solution.

Answer 16

Commodore 64 Basic, 4 bytes

1S|0

PETSCII substitution: | = SHIFT+Y

The zero page of a Commodore 64 is an area of 256 bytes of memory that can be accessed faster than the rest of RAM. Consequently, programs (such as the BASIC interpreter) use it for frequently-accessed data, and the CPU itself stores some of its internal state here. The contents are subject to change without notice.

The BASIC program above, ungolfed, is 1 SYS 0, ie. transfer execution to memory location 0. This starts executing the zero page as code. Normally, when the BASIC interpreter starts running a program, the first 16 bytes are

2F 37 00 AA  B1 91 B3 22
22 00 00 4C  00 00 00 00

so SYS 0 would execute the following

00: ROL-AND $37,A  - Undocumented opcode: rotate the value at memory location 0x37 left, and store the result in the accumulator
02: BRK            - Call the interrupt vector

The overall result is to output the BASIC READY. prompt and return control to the user. However, memory location 0x00 is the CPU's I/O direction register, and memory location 0x01 is CPU's I/O address register. If you've done something that changes these before running the program, the results can be unpredictable, ranging from outputting garbage to locking up the computer (the 0x22 usually contained in memory location 0x07, if executed as an instruction, is an undocumented HALT opcode).

Alternatively, a more reliably unpredictable program is the four-byte

1?TI

Prints the elapsed time, in jiffies (1/60 of a second), since system power-on.

Answer 17

PowerShell, 4 2 bytes

(crossed out 4 still looks like 4)

ps

This is the alias for Get-Process which will output the current process listing as a table, including handles, private memory, CPU time, etc.

Execute it via something like the following:

C:\Tools\Scripts\golfing>powershell.exe "ps"

Answer 18

Notepad, 1 keystroke

F5

Pressing F5 inserts the time and date in the format (h)h:mm XM (m)m/(d)d/yyyy. For example: 12:00 AM 1/1/1970

Answer 19

Baby Language, 0 bytes

I didn't submit this originally because I thought it postdated the question. I was wrong; the language did have an interpreter created in time. It's also probably the least cheaty 0-byte solution I've seen (given that a 0-byte program is specified to do exactly what the program asks, and not for the purpose of cheating on golfing challenges).

Baby Language is specified to ignore the program it's given and do something at random. (The interpreter linked on the Esolang page generates a random legal BF program and runs it.) That seems like a perfect fit for this challenge.

Answer 20

Zsh, 5 bytes

<<<$$

Prints PID.

Answer 21

C, 25 21 bytes

Thanks to pseudonym117 for saving 4 bytes.

main(i){putchar(&i);}

Compiled with gcc -o test lol.c (yeah I'm quite original with my file's name...), and ran with ./test.

It does what it says: prints the character corresponding to the memory address of i, which is defined at runtime, so it should be non-deterministic.

Answer 22

BrainfuckX and small s.c.r.i.p.t. (etc) polyglot - 2 bytes

?.

? - Randomize the value in the current cell

. - Send current cell to stdout

Answer 23

05AB1E, 2 bytes

žd

Try it online!

Outputs current microseconds from the executing machine's internal clock.

Or you could do something like this...

05AB1E, 3 bytes

A.r

Try it online!

Outputs a randomly shuffled lower-case alphabet.

Or this also works:

A.R

Try it online!

Outputs a random letter from the alphabet.

Or this also works, and is cooler:

05AB1E, 9 bytes

"ž"A.RJ.V

Try it online!

Outputs randomly one of these:

ž 23  > ža           push current hours
        žb           push current minutes
        žc           push current seconds
        žd           push current microseconds
        že           push current day
        žf           push current month
        žg           push current year
        žh           push [0-9]
        ži           push [a-zA-Z]
        žj           push [a-zA-Z0-9_]
        žk           push [z-aZ-A]
        žl           push [z-aZ-A9-0_]
        žm           push [9-0]
        žn           push [A-Za-z]
        žo           push [Z-Az-a]
        žp           push [Z-A]
        žq           push pi
        žr           push e
        žs           pop a, push pi to a digits (max. 100000)
        žt           pop a, push e to a digits (max. 10000)
        žu           push ()<>[]{}
        žv           push 16
        žw           push 32
        žx           push 64
        žy           push 128
        žz           push 256

Answer 24

Perl, 5 bytes

say$$

Outputs the process ID and a newline.

Answer 25

Python 2, 29 bytes

import os
print os.urandom(9)

Sadly not the first time writing code on a smartphone.

Answer 26

Ruby, 3 bytes

p$$

Try it online!

Prints the process ID.

Answer 27

Groovy, 9 bytes

{print{}}

Outputs:

Script1$_run_closure1@2c8ec01c

Because it outputs the memory address of the closure it is non-deterministic.

Answer 28

Pyke, 1 byte

C

Try it here!^[broken]
Try it Online!

Outputs the current time

Answer 29

Emotinomicon, 4 bytes

😀😅🎲⏬

Explanation:

😀😅🎲⏬
😀      push 0. Stack: [0]
  😅    push 1. Stack: [1]
    🎲  random[pop;pop]. Stack: [1 or 0]
      ⏬output

Answer 30

><>, 4 3 bytes

(crossed out 4 still looks like 4)

0nx

Try It Online!

Outputs some amount of 0's.

On an empty stack n throws an error and terminates the program. x chooses a random direction for the stack pointer. This means that for each 0 printed, there is a 50% chance for the program to exit.