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.

Answer 1

huh?, 5 characters

!hcuO

I actually have NO idea how it works, but 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!

Answer 2

Mathematica, 3 chars

a 2

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

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.

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!

Answer 5

Javascript: 34 characters

reifitnedi detcepxenU :rorrExatnyS

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

Answer 6

Python, 43 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

Answer 9

BASIC, 22 12 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: $!.

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.

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.

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).

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...

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

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...

Answer 21

UNIX shell, 31

Real solution at 52 characters:

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

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

6 chars + 25 = 31:

rev $0

Answer 22

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

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 119 92 74 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.

Answer 25

MS-DOS, 24 bytes

eman elif ro dnammoc daB

Output:

Bad command or file name

Answer 26

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 27

SmileBASIC, 118 102 bytes

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

Answer 28

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.

Answer 29

Windows command prompt, 93 bytes

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

Answer 30

JavaScript, 56

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