Programs that print their own source code

[PM 2Ring]

It can be a fun exercise to write a program that prints its own source code. It gets you thinking about the language syntax in ways that are a bit different to the usual programming problems. I couldn't find a thread on this topic here, so I thought it might be a nice idea to create one where we can put examples in all the different languages we are familiar with.

Try to avoid using fancy library functions as much as possible.

To get the ball rolling, here's one in Python.

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#! /usr/bin/env python

s='#! /usr/bin/env python\n\ns=%s\nprint s%%repr(s)'
print s%repr(s)

And a one line version that runs in the interpreter.

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s='>>> s=%s;print s%%repr(s)';print s%repr(s)

If you think using the repr() function is cheating, feel free to post an alternative.

I'll post one or two in PostScript a bit later. I've got one in C here (written by someone else) that is also a palindrome!

[Xanthir]

You're looking for the term 'quine'. There are a bunch of them out there. ^_^

[PM 2Ring]

You're looking for the term 'quine'. There are a bunch of them out there. ^_^

"To quine a phrase", to quine a phrase. I was introduced to W. V. O. Quine via Godel, Escher, Bach, which I recently started re-reading. But I didn't realize the term "quine" has become common jargon for programs like this.

So has this topic already been done here? If so, I certainly don't mind if the moderators merge or kill this thread.

I realize that there are many such self-reproducing programs scattered around the Net, but it'd be nice to have a bunch of them in one place. And it could be a fun game, especially for those who haven't tried it before.

[Lightnix]

Simple one in PHP:

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<?
$file = "quine.php";
$fh = fopen($file, 'r');
$data = fread($fh, filesize($file));
$data = htmlspecialchars($data);
fclose($fh);
echo 'Source: ' . $data;
?>

It could be improved by: adding new lines (<br />) in comments and just parsing the php start and end tags out - though that would be removing some of the source code from the output making the quine incomplete. It could also be improved by parsing the URL to find out what its file name is rather than having it hardcoded in.

But I'm too lazy for that.

[HenryGifford]

Yeah in Python I did:

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quine=open("quine.py")
quine=quine.read()
print quine

[Why Two Kay]

I'm pretty sure a restriction on quines is that they are not supposed to use files.

[Ended]

...I don't think reading in and printing the source file is quite in the spirit of the challenge. (Although I don't think I can do any better )
[Edit: ninja'd]

For extra difficulty, try iterating quines:

Source file A is in language X.
When A compiled and run, it outputs source file B in language Y.
When B is compiled and run, it outputs A.

[jaap]

You're looking for the term 'quine'. There are a bunch of them out there. ^_^

Such as in this thread in the computer science forum.

[hotaru]

is this cheating?

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[ " dup pprint call" print ] dup pprint call

[sparkyb]

In college I had a class where we had to do something similar to this. They couldn't make it this easy though. Instead it worked as follows. Given a function that takes a string as input and produces some output, write a program that when run produces as output the same thing that the given function would produce if the source code to this program were passed to it as the input string (the normal quine would be the trivial case of this where the function just directly prints its input). Actually, the assignment was write a program than given as input the source code to a function as described above generates a program as described above to match that particular function. The way it was described was that if you call the function that takes the program as input "eat" and if you call the program "self" then self()==eat(self), roughly speaking. And the meta program that we were supposed to write that given some "eat" function generates the matching "self" program was called an autocannibalizer. Anyone else need an asprin now?

[PM 2Ring]

...I don't think reading in and printing the source file is quite in the spirit of the challenge.

Indeed.

You're looking for the term 'quine'. There are a bunch of them out there. ^_^

Such as in this thread in the computer science forum.

Thanks, guys.

[evilbeanfiend]

I'm pretty sure a restriction on quines is that they are not supposed to use files.

yes reading your source code from file is usually forbidden as its trivial in any language which allows it (so all useful ones). also empty programs are usually disallowed as these are also trivially quines in some languages e.g.

in TCL

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[HenryGifford]

I'm pretty sure a restriction on quines is that they are not supposed to use files.

Ah bummer.

[Filius Nullius]

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#include <stdio.h>
char *program = "#include <stdio.h>%cchar *program = %c%s%c;%cint main()%c{%c
printf(program, 10, 34, program, 34, 10, 10, 10, 10, 10, 10);%c    return 0;%c}%c";
int main()
{
        printf(program, 10, 34, program, 34, 10, 10, 10, 10, 10, 10);
        return 0;
}



I think the above is a standard solution to the problem of a program printing it's own source, this isn't my solution but I don't remember where I found it.

[Notch]

For extra difficulty, try iterating quines:

I once wrote a java program that, when run, spits out the source code for a brainfuck program that, when run, spits out the source code for the original java program.

[Main]

Here's some in Lisp. Being lisp code, they're more expressions that return their own source than programs that print it, but the idea is the same. Besides, "program" in lisp isn't well-defined.

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((lambda (x) (list x x)) (lambda (x) (list x x)))

I think this is valid Scheme. I like this one, it's very elegant.

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(let ((let '`(let ((let ',let)) ,let))) `(let ((let ',let)) ,let))

This one is in Common Lisp.

I think for Common Lisp, using #n# and #n= is probably cheating. Using '- is definitely cheating; (symbol-value '-) is the value of the expression currently being evaluated, so it makes quines really easy.

If anyone's got any more lisp quines, I'd like to see them.

[Berengal]

Probably doesn't count as a proper quine, but in prolog 'Quine = quine.' will produce "Quine = quine." in the interpreter. (Depending on which interpreter you're using it may also print "Yes" or "true" or something to that effect. It doesn't in mine).

I once wrote a python function that would redefine itself each time it was run, producing different results. It was something as simple as 'def foo(): global foo; s = "<foo source>"; <modify s>; foo = eval(s)' but with some additional effects thrown in.

[Cosmologicon]

Here's an impressive period-4 iterating quine in C that was an IOCCC winner in 2000. Each of the 4 programs has an interesting layout.

[Main]

There was a link in the other thread to a page full of them:
http://www.nyx.net/~gthompso/quine.htm
They're in various languages. Here's some of the more interesting common lisp ones:

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#1=(WRITE '#1# :CIRCLE T)
#1=(SETQ *PRINT-CIRCLE* '#1#)

#1='#1# ; Only if *print-circle* is already non-nil

These all use circular-object syntax.

This one's technically common lisp, but it's really written in FORMAT:

(format t "~@?" "(format t \"~~@?\" ~:*~S)")

Like the WRITE one above, it prints it's source.

[PM 2Ring]

I'll post one or two in PostScript a bit later. I've got one in C here (written by someone else) that is also a palindrome!

A PostScript program which outputs itself to the console:

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/s
(
[(/s)<28>s<29>(def)s]{=}forall
)
def
[(/s)<28>s<29>(def)s]{=}forall


And this PostScript one prints itself to the output device:

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/Times-Roman findfont 9 scalefont setfont 9 700 moveto
/s
(
[(/Times-Roman findfont 9 scalefont setfont 9 700 moveto)(/s)<28>s<29>(def)s]{gsave show grestore 0 -20 rmoveto}forall showpage
)
def
[(/Times-Roman findfont 9 scalefont setfont 9 700 moveto)(/s)<28>s<29>(def)s]{gsave show grestore 0 -9 rmoveto}forall showpage


Here's the palindrome in C, written by Thad Smith. Note: this is all on one line.

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/**/char q='"',*a="*//**/char q='%c',*a=%c%s%c*/};)b(stup;]d[b=]d-472[b)--d(elihw;)q,a,q,q,2+a,b(ftnirps;)b(stup{)(niam;731=d tni;]572[b,",b[275];int d=137;main(){puts(b);sprintf(b,a+2,q,q,a,q);while(d--)b[274-d]=b[d];puts(b);}/*c%s%c%=a*,'c%'=q rahc/**//*"=a*,'"'=q rahc/**/


[Random832]

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#!/bin/cat
Any text so it's not a blank file.

And, just to provide an entry that isn't cheating - a cheap trick is to provide a copy of most of the source code as a string literal, and then use that in the output along with code to convert it to a string literal for the bit where you put the strings.

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public class Hello1{static string[] s={"public class Hello1{stati
c string[] s={","};public static void Main(){System.Console.Write
Line(s[0]+\"\\\"\"+s[0].Replace(\"\\\\\",\"\\\\\\\\\").Replace(\"
\\\\\",\"\\\\\\\"\")+\"\\\",\\\"\"+s[1].Replace(\"\\\\\",\"\\\\\\
\\\").Replace(\"\\\\\",\"\\\\\\\\\")+\"\\\"\"+s[1]);}}"};public s
tatic void Main(){System.Console.WriteLine(s[0]+"\""+s[0].Replace
("\\","\\\\").Replace("\\","\\\"")+"\",\""+s[1].Replace("\\","\\\
\").Replace("\\","\\\\")+"\""+s[1]);}}

Remove all linebreaks.

[qbg]

Yet another Common Lisp solution I just came up with:

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(macrolet ((do-self (&body body)
             `(progv '(*self*) '((do-self ,@body))
                (eval '(progn ,@body)))))
  (do-self
   `(macrolet ((do-self (&body body)
                 `(progv '(*self*) '((do-self ,@body))
                    (eval '(progn ,@body)))))
      ,*self*)))


EDIT: Or something simpler:

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(let ((a '(lambda (a)
            `(let ((a ',a))
               (funcall (compile nil a) a)))))
  (funcall (compile nil a) a))


[FatPhil]

Stick this in your nearest shell:

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dc -e'[[dc -e]P39P91PP93P[dx]P39PAP]dx'

(I of course have a pure dc quine too, but that's too short and simple to be interesting.)

[TheChewanater]

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[You, sir, name?]

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#!/bin/bash
# fish in barrel, meet stick of dynamite:
cat $0

[tekk]

I'm surprised noone's used the best tool for this job, aside from the genius who first came up with using cat

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#!/usr/bin/perl

open(source, "./printsrc");
@src = <source>;
print(@src);


yay perl =D

[You, sir, name?]

:shock: I'm surprised noone's used the best tool for this job, aside from the genius who first came up with using cat

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#!/usr/bin/perl

open(source, "./printsrc");
@src = <source>;
print(@src);


yay perl =D

Ah, but that fails if you change the file name. Mine doesn't.

[tekk]

:shock: I'm surprised noone's used the best tool for this job, aside from the genius who first came up with using cat

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#!/usr/bin/perl

open(source, "./printsrc");
@src = <source>;
print(@src);


yay perl =D

Ah, but that fails if you change the file name. Mine doesn't.

I honestly just cannibalized my game for that code I'll have to think of a way to fix that

[Random832]

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#!/bin/cat
cat $0 is for weenies - cut out the middleman.

[Earlz]

Sadly I can't contribute(I'm not good at such problems) but I have a request.

Can someone please make a self-printing BF program? lol

[phlip]

Second link in Google.

[You, sir, name?]

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#!/bin/cat
cat $0 is for weenies - cut out the middleman.

But cat is an integral part of shell scripting! Okay, so how about this one.

Everything beyond the first line is valid C and valid bash code, and the bash code compiles itself as a C program that works like a limited version of cat, which can be used to print it's own sources.

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#!/bin/bash
#if 0
file=`mktemp`
tail -n+2 $0 | cc -o $file -x c -
$file < $0
rm $file
exit
#endif
#include <stdlib.h>
#include <stdio.h>

int main(int argc, char *argv[]) {
        for(;;) {
                int c = getchar();
                if(c == EOF) break;
                putchar(c);
        }

        return EXIT_SUCCESS;
}


[Squid Tamer]

I heard of some guy who won a competition like this just by his program being:

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hi

When it's run it has an error and returns the culprit line: the only one there.
I think that this competition had no official rules, no there was nothing to stop him.

Yes, I would count it as cheating, but still thought it was funny.

[phlip]

Hmm... in that vein, this file:

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tmp.c:1: error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token
tmp.c:1:41: warning: multi-character character constant
tmp.c:1:50: warning: character constant too long for its type

when saved as "tmp.c" and compiled with:

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LC_ALL=C gcc tmp.c 2>&1

(the LC_ALL=C is required in Unicode terminals, otherwise the error messages come out with smart quotes instead of ASCII quotes) comes out with the same output as its input. Sort of a GCC quine, rather than a C quine.

I'm interested to know what compiler you were using where an input of "hi" came out with an error message of merely "hi"... no other messages at all.

[PM 2Ring]

I'm interested to know what compiler you were using where an input of "hi" came out with an error message of merely "hi"... no other messages at all.

Me, too. Maybe this happened a long time ago on some odd interpreter-based system.

I could imagine a BASIC interpreter that used "hi" as the prompt, intstead of the usual Ok. And it could ignore "hi" alone on a line as a harmless syntax error.

Back in the day, most BASICs would spit out a simple message on a syntax error, and so if you typed the syntax error message at the interpreter, it'd spit it back out at you. This is the most likely scenario for the story above, IMHO, but the details have become altered as the tale was passed around.

[Random832]

Using the Microsoft C# compiler...

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Microsoft (R) Visual C# 2008 Compiler version 3.5.30729.1
for Microsoft (R) .NET Framework version 3.5
Copyright (C) Microsoft Corporation. All rights reserved.

foo.cs(1,23): error CS1040: Preprocessor directives must appear as the first
        non-whitespace character on a line
foo.cs(1,1): error CS0116: A namespace does not directly contain members such as
        fields or methods
foo.cs(7,45): error CS1514: { expected
foo.cs(10,40): error CS1513: } expected


[TheChewanater]

Creative, but a quine is "A program that prints it's own source code when run". These neither run nor print their source code (the compilers do).

[You, sir, name?]

Creative, but a quine is "A program that prints it's own source code when run". These neither run nor print their source code (the compilers do).

That's compiled langauges though. In interpreted languages, there is very little to distinguish between "the program caused the interpreter to print" and "the program prints".

[Random832]

How about...

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C:\foo.exe is not a valid Win32 application.

Save to the file "C:\foo.exe", or adjust the content accordingly.

[TheChewanater]

Creative, but a quine is "A program that prints it's own source code when run". These neither run nor print their source code (the compilers do).

That's compiled langauges though. In interpreted languages, there is very little to distinguish between "the program caused the interpreter to print" and "the program prints".

Well, it translates it into machine code, right? If it cannot do this and the interpreter prints this out, I don't think it's a quine.