Print your code backwards - reverse quine

Question

Write a program that prints its own source code out backwards, in other words an eniuq.

Scoring:

• +50 if you use pull data from the Internet.
• +25 if you read your own source code.
• +1 point per character
• Lowest score wins.

Rules:

• No using other files (e.g. reverse.txt)
• Minimum code length is two characters.
• Your program cannot be a palindrome.

• Iszi: Looks like this has been done before, just without the "no palindromes" rule.
• ike: They are penalties.
• AJMansfield: The one question I have, then, is why is pulling data from the internet given a larger penalty than reading the source file?
• hildred: I posted the challenge codegolf.stackexchange.com/questions/16043/… which has tighter rules than this one, so every answer there would qualify as an answer here, but would not score as well. My current answer there is over 6000 characters.
• mbomb007: @lebatsnok You could move your comment to an answer now. :)

Answer 1

huh?, 5 characters

!hcuO

(削除) I actually have NO idea how it works, but (削除ここまで) If you download the interpreter, and if you write !hcuO, then you get Ouch!

To run this, you need to execute the program like this:

huh.exe !hcuO

It will actually look for a file called !hcuO, but it doesn't exist, so it outputs Ouch!

• Iszi: Is it not just a little ironic that you don't understand how your own code works, in an esolang that by design isn't supposed to understand your code either?
• AJMansfield: @Iszi That's the joke.
• Iszi: I'm not sure you're using huh? right, though I'm having a hard time finding proper documentation. It seems the usage is intended to be huh.exe <path to source code> and Ouch! is returned for an invalid path. Try putting your code into an actual file, and feeding that file as an argument to huh? and see what happens. It's also interesting to see that it generates a Notes.txt file with some commentary.
• Iszi: Ok, this thing just told me it thinks it understands but I didn't see anything happen. Maybe I should stop toying with it on my primary system.
• MilkyWay90: What if there IS a file name !hcuO?

Answer 2

Mathematica, 3 chars

a 2

a 2 means a times 2. So the answer is 2 a.

• ike: This will probably win unless someone can get a two char solution.
• alephalpha: In fact I know a two char solution. Also in Mathematica: 1#. The output is #1.
• user3094403: @alephalpha: Then you should post that as an answer!

Answer 3

GolfScript - 2

1

(ie \n1 where \n is the newline character)

Output:

1

(ie 1\n)

---

To quote Ilmari:

GolfScript automatically appends a newline to the end of the output

Thus a newline followed by a number will print the number followed by a newline.

• Kaya: +1 I didn't think anything could beat the Mathematica solution.
• user36219: Pretty boring solution...
• rydwolf: @theonlygusti It's golfscript, whaddya expect...

Answer 4

H9+, 13 characters

!dlrow ,olleH

As the web page says, all characters that are not H, 9 or + are ignored, so my program will print Hello, world!

• totymedli: The one and only practical benefit of crazy esoteric languages is to answer these crazy questions.
• kojiro: It'd be more practical if these questions were so.
• user36219: That's pretty darned clever!
• Makonede: According to the JS implementation, H seems to output hello, world\n, therefore your code should be \ndlrow ,olleh, with no bytes added.

Answer 5

Javascript: 34 characters

reifitnedi detcepxenU :rorrExatnyS

outputs SyntaxError: Unexpected identifier, at least in the Chrome console

• Eliseo D'Annunzio: Clever use of abusing the system through error abuse
• major-mann: You sir, have made my day :D
• o0'.: Not an original idea, there already was an answer about this in python 2.
• scrblnrd3: @Lohoris Sorry, I didn't see that one
• kenorb: Firebug console in Mozilla Firefox: tnemetats erofeb ; gnissim :rorrExatnyS => SyntaxError: missing ; before statement.

Answer 6

Python, (削除) 43 (削除ここまで) 41

_=']0~::[_%%_ tnirp;%r=_';print _%_[::~0]

Answer 7

Mathematica, 2 bytes

1#

Outputs:

#1

Answer 8

TI-BASIC, 2

i2

Where i is the imaginary number.

Outputs 2i

• kernigh: This only works in the home screen, not inside a PRGM.
• AJMansfield: @kernigh Did you try it? It works fine. (If the last statement of a TI-BASIC program evaluates as an expression, its result is printed instead of 'Done' when the program terminates)

Answer 9

BASIC, (削除) 22 (削除ここまで) (削除) 12 (削除ここまで) 7 characters

:-)

1 enil ni rorre xatnyS

EDIT: If you're allowed to enter the program in immediate mode, then this could be reduced to rorre xatnyS (12 characters).

In BBC BASIC, you only need 7 characters:

ekatsiM

Answer 10

ksh (21 chars)

$ dnuof ton :found :hsk
ksh: dnuof: not found

---

bash (31 chars)

$ dnuof ton dnammoc :found :hsab-
-bash: dnuof: command not found

---

sh (29 chars)

$ dnuof ton dnammoc :found :hs-
sh: dnuof: command not found

This one could not work on some Linux distributions, but works on OSX.

---

tcsh (26 chars)

$ .dnuof ton dnammoC :found.
.dnuof: Command not found.

---

csh (26 chars)

% .dnuof ton dnammoC :found.
.dnuof: Command not found.

---

Above should work on all *unix based OS.

---

Assumptions:

• You don't have dnuof command or alias present.

---

bash (2-4 chars)

This one most likely doesn't qualify, but I'll share it as curiosity.

Assuming the previous shell command in Bash was $!. The following command:

!$

will produce: $!.

• Kroltan: Doesn't work for me, i have a command named dnuof
• kenorb: I forgot to add, it doesn't work on distributions which has dnuof installed (whatever it is). Damn hackers.
• Doorknob: Hahaha, there's a command named dnuof? :D what does it do?
• user85052: From the name I can tell dnuof = (d)aily (n)ew (u)ser (of). This outputs how many users have been created on this computer today. Its arguments filter which computer(s) on the Internet to show for the daily new users. (The computer names are decoded by the program; each computer is given a different name.) (.dnuof is an alias for dnuof.)
• Tomas: ha ha this is funny :))

Answer 11

C++ 472 characters

A lot of characters but I cant think of a simpler way in a c-based language.

#include<iostream>
#include<string.h>
#define p(t) std::cout<<'}'<<';'<<')'<<strrev(&std::string(#t)[0])<<t;
char* strrev(char*p){char*t=p;char*q=p;while(q&&*q)++q;for(--q;p<q;++p,--q)*p=*p^*q,*q=*p^*q,*p=*p^*q;return t;}
int main(){p("(p{)(niam tni};t nruter;q*^p*=p*,q*^p*=q*,q*^p*=p*)q--,p++;q<p;q--(rof;q++)q*&&q(elihw;p=q*rahc;p=t*rahc{)p*rahc(verrts *rahc;t<<)]0[)t#(gnirts::dts&(verrts<<')'<<';'<<'}'<<tuoc::dts )t(p enifed#>h.gnirts<edulcni#>maertsoi<edulcni#");}

Answer 12

GolfScript, 12 chars

"-1%.`"-1%.`

This code takes the double-quoted string "-1%.`", reverses it (-1%), duplicates it (.) and un-evals (`) the second copy, restoring the double quotes around it.

Previous entry (13 chars):

{`'.~'+-1%}.~

Based on the 8-char quine {'.~'}.~ from this answer; the extra 5 chars are needed to stringify and reverse the output.

Ps. Note that GolfScript automatically appends a newline to the end of the output. If this is counted as part of the output, a corresponding newline can be prepended to either version of the code without affecting the output, for a cost of one extra char.

Answer 13

Befunge 98 - 10 chars

"8k,'!1+,@

This works if your interpreter does not interpret wrapped lines after " as adding an extra space. If your interpreter does interpret wrapped lines like that, then this 11 char solution works (because duplicate spaces in a string literal are interpreted as one):

"9k,'!1+,@ 

---

If I can use g without penalty, then these also work (7 and 8 chars respectively):

"5k,g,@

and

"6k,g,@ 

Answer 14

Fission, 6 bytes

A rare case of a generalised quine that is the same length as the normal quine:

"LO+!'

The idea is the same as that of the normal quine, but we're using a left-going atom (starting at the L) so that print mode traverses the code in the opposite order.

Answer 15

Ruby, 60

puts(2,s=<<2.chop.reverse,s)
puts(2,s=<<2.chop.reverse,s)
2

Based on a classic Ruby quine.

• Jon Purdy: Nice use of heredocs.

Answer 16

Perl, 41

$_=q{print~~reverse"\$_=q{$_};eval"};eval

Old 52 character answer (27+25 penalty)

open+0;print ~~ reverse <0>

Reads its own source, stores the reverse in a scalar, and prints that.

• breadbox: The scalar operator can be replaced by ~~. However, you need to add +25 to your score for reading your own source code.
• smcg: @breadbox noted
• Tomas: +1. I was about to post something like my shell solution: $_='say"lave;047円",~~reverse,"047円=_\$"';eval, but your solution is shorter :-) Note that you can golf it down to 39 characters using say. Hope you will beat all the esoteric weirdness :-)
• smcg: @Tomas are you suggesting replacing print with say? That ends up not printing anything.
• Tomas: Did you run perl with -Mfeature=say option?

Answer 17

J: 26

Standard quining (26 chars): by defining a function and passing it its own definition, in quotes:

|.(,],2#{:)'|.(,],2#{:)'''

Could probably be made shorter.

J-specific (33 chars): by defining a variable and asking what file the variable was defined in, i.e. this one, then printing out the contents of that file:

1!:2&2|.1!:1(4!:4 a=:<'a'){4!:3''

Must be saved & run from a script (i.e. not in the REPL, because then the answer to the question is "your argument wasn't defined in a file", so there's no file to read).

• Johannes Kuhn: The second one should get the + 25 bonus to read the own file.
• jazzpi: @JohannesKuhn: Penalty, but yeah.
• Johannes Kuhn: "Bonus" sounds nicer.

Answer 18

><>, 25 bytes

I was surprised to find this hadn't been done yet. :)

...yhsif sllems gnihtemoS

Paste code here and run it.

. is the Jump command, popping x and y off the stack, and moving the IP to (x, y) in the code box. In this case, the stack is empty, so the language's only error message is printed:

Something smells fishy...

• Insane: The best answer

Answer 19

Microscript, 11 bytes

I kind of had to do this.

0"Caxq"Caxq

Surprisingly, this is actually shorter than the language's shortest known true quine. q and a are otherwise equivalent, except q adds wrapping quotes while a does not.

Answer 20

Windows 10 .EXE, 98 bytes

.rehsilbup erawtfos eht htiw kcehc ,CP ruoy htiw noisrev a dnif oT
.CP ruoy no nur t'nac ppa sihT

enter image description here

• The Empty String Photographer: Is there a version for my PC?

Answer 21

PHP, 41 characters (+25)

Don't know if I understood the assignment correctly. But here's a PHP try:

while(!isset($s) || $s) echo isset($s) ? array_pop($s) : ($s = str_split(file_get_contents(__FILE__)) and null);

edit: this can be much shorter:

echo strrev(file_get_contents(__FILE__));

But since it can be that simple, this is probably not what is being asked...

• nl-x: phpFiddle: phpfiddle.org/main/code/fuy-mv0
• Justin: When I click run, I get a whole bunch of useless nonsense (here is a short snippet of it: >? ;)llun dna ))__ELIF__(f$(tilps_rts = s$( : )s$(pop_yarra ? )s$(tessi ohce )s$ || )s$(tessi!(elihw ;"stnetnoc_"=.f$ ;'teg_elif'=f$ php?<>?}};ESLAF nruter;"ec6x\i66x02円x\e47x96円x\rw ; there is much much more). Also, include your character count; this is a code golf. Also, it seems that you are reading your source file, so add 25 to your character count and that is your score. Lowest score wins.
• nl-x: @Quincunx First off, it is backwards ... but secondly, this is the source code that phpfiddle generates! (but backwards...) They seem to escape a lot of thing, trying to keep things safe. Replace array_pop with array_shift to see the source code not backwards...
• Justin: Yes I can see the reversed source code, but what is with all the extraneous text? There are a lot of escape sequences, but there are some that aren't (eg: ESLAF nruter ie return FALSE).
• nl-x: @Quincunx Sorry, I'm not catching if you are showing interest in the way phpFiddle works, or if you are criticizing my code. If it's the latter, then in my defense, put my code in a .php file and run it in a browser, and it'll work cleanly. I just thought phpfiddle was a nice thing to let you see, so you can see a bit of it's inner workings.

Answer 22

UNIX shell, 31

Real solution at 52 characters:

A='printf "A$ lave;047円`echo $A|rev`047円=A"';eval $A

But beware! Honesty doesn't pay off in today's world! Penalty is too low!!

6 chars + 25 = 31:

rev 0ドル

• kenorb: On OSX rev 0ドル generates the error: rev: illegal option -- b.

Answer 23

MATLAB, 78 characters:

 
|
.snoisserpxe ro stnemetats BALTAM ni dilav ton si retcarahc tupni ehT :rorrE

Note that the solution requires you to begin with a special character (alt+0160) and that it prints exactly the reversed message. (Unlike the python solution)

Answer 24

JavaScript jQuery (削除) 119 (削除ここまで) (削除) 92 (削除ここまで) (削除) 74 (削除ここまで) 70 characters

alert($("#answer-16051 pre code").text().split("").reverse().join(""))

Now using jQuery, as minitech suggested in the comments, and manually wrapping with <pre><code> so I can use text() without fear of other code blocks in this post interfering. Manually wrapping with <h4> was incompatible with chromeium when I tested it, so now it should work in most browsers.

This program, if run from this page, finds the code block directly above, reverses its contents, and puts it in an alertbox.

Its easy enough to verify, just paste it into the dev console.

• Ry-: This is way longer than just using a function. And you should use jQuery (on this page) or at least querySelector anyways...
• AJMansfield: @minitech thanks for the tip, I swapped it for a querySelector now. I would like to look into the jQuery possibility, but it looks like it will take a little longer for me to figure out.
• AJMansfield: @minitech ok, thanks for the jQuery tip. (I only started learning javascript yesterday.)
• user36219: I like this solution; thinking outside the box.

Answer 25

MS-DOS, 24 bytes

eman elif ro dnammoc daB

Output:

Bad command or file name

Answer 26

Windows command prompt, 93 bytes

.elif hctab ro margorp elbarepo ,dnammoc lanretxe ro lanretni na sa dezingocer ton si 'file.'

enter image description here

Answer 27

JavaScript, 62

function f(){alert((f+'f()').split('').reverse().join(''))}f()

Works for me on latest Chrome (v 31.0.1650.63). Some other browsers may give a different output. (If you reverse that output, then it would work :P)

Answer 28

SmileBASIC, (削除) 118 (削除ここまで) 102 bytes

FOR I=-101TO.?MID$(("+CHR$(34))*3,30,102)[-I];:NEXTFOR I=-100TO.?MID$(("+CHR$(34))*3,30,102)[-I];:NEXT

Answer 29

Japt, 12 bytes

"iQ 2w"iQ 2w

Try it online!

Based off the standard Japt quine

Explanation

"iQ 2w" // Take this string. iQ 2w
 iQ // Insert a quote. "iQ 2w
 2 // Double. "iQ 2w"iQ 2w
 w // Reverse. w2 Qi"w2 Qi"
 // Implicitly output.

• Shaggy: Congrats on your 5th Japt solution; bounty on its way.
• ASCII-only: @Shaggy wait >_> I wasn't doing this for the bounty
• Shaggy: Happy coincidentally for you, so, that there's one going :)

Answer 30

JavaScript, 56

($=_=>_!=$._?_?$(_.slice(1))+_[0]:')':$('($='+$+')('))()

• George Reith: Please state your environment because this does not work in Chrome. Is this Rhino or what?
• Ry-: @GeorgeReith: Anything with ES6 arrow function support. All SpiderMonkeys should work fine, for example (Rhino included).