Quine

Quine is a programming puzzle. It lays out a problem which Rosetta Code users are encouraged to solve, using languages and techniques they know. Multiple approaches are not discouraged, so long as the puzzle guidelines are followed. For other Puzzles, see Category:Puzzles.

Print out a program's own source code. Since this is a puzzle, shorter/more efficient versions are encouraged along side more obvious versions.

This task has been flagged for clarification. Code on this page in its current state may be flagged incorrect once this task has been clarified. See this page's Talk page for discussion.

Ada

with Ada.Text_Io; use Ada.Text_Io;

procedure Quine is
   Line   : String(1..80);
   Length : Natural;
   File   : File_Type;
begin
   Open(File => File, Name => "Quine.adb", Mode => In_File);
   while not End_Of_File(File) loop
      Get_Line(File => File, Item => Line, Last => Length);
      Put_Line(Line(1..Length));
   end loop;
end Quine;

The following example is a quine without reading the source file.

with Text_Io;
procedure Self is 
   Q:Character:='"';
   A:String(1..132):="with text_io;procedure self is q:character:=;a:string(1..132):=;begin text_io.put_line(a(1..45)&q&a(46..65)&q&a&q&a(66..132));end;"; begin 
   Text_Io.Put_Line(A(1..45)&Q&A(46..65)&Q&A&Q&A(66..132));
end;

Befunge

The code space is also the data space of a Befunge program. Programs can be read and modified on the fly. This quine works by reading and printing each character of the source. (This is a implicit loop, since the Befunge codespace wraps around.)

:0g,:66+`#@_1+

Forth

SOURCE TYPE

Haskell

The obvious solution, as a one-liner:

let q s = putStrLn $ s ++ show s in q "let q s = putStrLn $ s ++ show s in q "

Having the string at the end makes things a bit simpler than in generic version mentioned in the Wikipedia article.

Haskell does not keep the code in an uncompiled-equivalent form around at runtime, so the "quotation trick" has to be used.

Java

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class Quine{
	public static void main(String[] args){
		try{
			BufferedReader input = new BufferedReader(
					new FileReader("Quine.java"));
			String line;
			while((line = input.readLine())!=null){
				System.out.println(line);
			}
		}catch(FileNotFoundException e){
			e.printStackTrace();
		}catch(IOException e){
			e.printStackTrace();
		}
	}
}

Perl

This example retrieves the name of the source file from the $0 variable, which represents the file path and name used to invoke the script.

#!/usr/bin/perl
open FILE, "< $0" or die "Failed to open self\n";
map { print $_ } <FILE>;
close FILE;

Assuming the code is saved in the file quine.pl, this works when executed as

./quine.pl

or

perl quine.pl

but fails when fed to the perl interpreter's standard input as

cat quine.pl|perl

If we may assume that the source file is named "quine.pl", replacing

open FILE, "< $0" or die "Failed to open self\n";

with

open FILE, "< quine.pl" or die "Failed to open self\n";

will allow us to execute the code through the interpreter's standard input:

cat quine.pl|perl

PHP

This example obtains its own filename from the __FILE__ built-in variable.

<?
$fh = fopen( __FILE__, 'r' );
echo fread($fh, filesize(__FILE__));
fclose( $fh );
?>

Strictly speaking, however, the example prints more than its own source code. Because PHP is designed to service HTTP requests, the output looks like this:

X-Powered-By: PHP/5.2.3-1ubuntu6
Content-type: text/html

<?
$fh = fopen( __FILE__, 'r' );
echo fread($fh, filesize(__FILE__));
fclose( $fh );
?>

(The X-Powered-By line will vary from system to system.)

Seed7

$ include "seed7_05.s7i";
const array string: prog is [](
"$ include \"seed7_05.s7i\";",
"const array string: prog is [](",
"const proc: main is func",
"  local var integer: number is 0;",
"  begin",
"    for number range 1 to 2 do writeln(prog[number]); end for;",
"    for number range 1 to 11 do",
"      writeln(literal(prog[number]) <& \",\");",
"    end for;",
"    writeln(literal(prog[12]) <& \");\");",
"    for number range 3 to 12 do writeln(prog[number]); end for;",
"  end func;");
const proc: main is func
  local var integer: number is 0;
  begin
    for number range 1 to 2 do writeln(prog[number]); end for;
    for number range 1 to 11 do
      writeln(literal(prog[number]) <& ",");
    end for;
    writeln(literal(prog[12]) <& ");");
    for number range 3 to 12 do writeln(prog[number]); end for;
  end func;

Original source: [1]

UNIX Shell

#!/bin/sh
cat "$0"