Editing Polyglot (computing) (section)

==Examples==

===C, PHP, and Bash===

Two commonly used techniques for constructing a polyglot program are to make use of languages that use different [[Character (computing)|characters]] for [[comment (computer programming)|comments]], and to redefine various tokens as others in different languages. These are demonstrated in this [[public domain]] polyglot written in [[ANSI C]], [[PHP]] and [[Bash (Unix shell)|bash]]:
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'''Highlighted for Bash'''
<syntaxhighlight lang="bash">
 #define a /*
 #<?php
 echo "\010Hello, world!\n";// 2> /dev/null > /dev/null \ ;
 // 2> /dev/null; x=a;
 $x=5; // 2> /dev/null \ ;
 if (($x))
 // 2> /dev/null; then
 return 0;
 // 2> /dev/null; fi
 #define e ?>
 #define b */
 #include <stdio.h>
 #define main() int main(void)
 #define printf printf(
 #define true )
 #define function
 function main()
 {
 printf "Hello, world!\n"true/* 2> /dev/null | grep -v true*/;
 return 0;
 }
 #define c /*
 main
 #*/
</syntaxhighlight>
{{column}}
'''Highlighted for PHP'''
<syntaxhighlight lang="PHP">
 #define a /*
 #<?php
 echo "\010Hello, world!\n";// 2> /dev/null > /dev/null \ ;
 // 2> /dev/null; x=a;
 $x=5; // 2> /dev/null \ ;
 if (($x))
 // 2> /dev/null; then
 return 0;
 // 2> /dev/null; fi
 #define e ?>
 #define b */
 #include <stdio.h>
 #define main() int main(void)
 #define printf printf(
 #define true )
 #define function
 function main()
 {
 printf "Hello, world!\n"true/* 2> /dev/null | grep -v true*/;
 return 0;
 }
 #define c /*
 main
 #*/
</syntaxhighlight>
{{column}}
'''Highlighted for C'''
<syntaxhighlight lang="c">
 #define a /*
 #<?php
 echo "\010Hello, world!\n";// 2> /dev/null > /dev/null \ ;
 // 2> /dev/null; x=a;
 $x=5; // 2> /dev/null \ ;
 if (($x))
 // 2> /dev/null; then
 return 0;
 // 2> /dev/null; fi
 #define e ?>
 #define b */
 #include <stdio.h>
 #define main() int main(void)
 #define printf printf(
 #define true )
 #define function
 function main()
 {
 printf "Hello, world!\n"true/* 2> /dev/null | grep -v true*/;
 return 0;
 }
 #define c /*
 main
 #*/
</syntaxhighlight>
{{columns-end}}

Note the following:
*A hash sign marks a [[preprocessor]] statement in C, but is a comment in both bash and PHP.
*"//" is a comment in both PHP and C and the [[root directory]] in bash.
*Shell [[Redirection (computing)|redirection]] is used to eliminate undesirable outputs.
*Even on commented out lines, the "<code>&lt;?php</code>" and "<code>?&gt;</code>" PHP indicators still have effect.
*The statement "<code>function main()</code>" is valid in both PHP and bash; C #defines are used to convert it into "<code>int main(void)</code>" at compile time.
*Comment indicators can be combined to perform various operations.
*"<code>if (($x))</code>" is a valid statement in both bash and PHP.
*<code>[[printf (Unix)|printf]]</code> is a bash [[shell builtin]] which is identical to the [[printf format string|C printf]] except for its omission of brackets (which the [[C preprocessor]] adds if this is compiled with a [[C compiler]]).
*The final three lines are only used by bash, to call the <code>main</code> function. In PHP the <code>main</code> function is defined but not called and in C there is no need to explicitly call the <code>main</code> function.

===SNOBOL4, Win32Forth, PureBasicv4.x, and REBOL===

The following is written simultaneously in [[SNOBOL]]4, [[Forth (programming language)|Win32Forth]], [[PureBasic]]v4.x, and [[REBOL]]:

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'''Highlighted for SNOBOL'''
<syntaxhighlight lang="snobol">
 *BUFFER : A.A ; .( Hello, world !) @ To Including?
 Macro SkipThis; OUTPUT = Char(10) "Hello, World !"
 ;OneKeyInput  Input('Char', 1, '[-f2-q1]')  ; Char
 End; SNOBOL4 + PureBASIC + Win32Forth + REBOL = <3
 EndMacro: OpenConsole() : PrintN("Hello, world !")
 Repeat : Until Inkey() :  Macro SomeDummyMacroHere
 REBOL  [ Title:  "'Hello, World !' in 4 languages"
 CopyLeft:  "Developed in 2010 by Society" ]  Print
 "Hello, world !"  EndMacro:  func  [][]  set-modes
 system/ports/input [binary: true] Input  set-modes
 system/ports/input  [binary: false] NOP:: EndMacro
 ; Wishing to refine it with new language ? Go on !
</syntaxhighlight>
{{column}}
'''Highlighted for Forth'''
<syntaxhighlight lang="forth">
 *BUFFER : A.A ; .( Hello, world !) @ To Including?
 Macro SkipThis; OUTPUT = Char(10) "Hello, World !"
 ;OneKeyInput  Input('Char', 1, '[-f2-q1]')  ; Char
 End; SNOBOL4 + PureBASIC + Win32Forth + REBOL = <3
 EndMacro: OpenConsole() : PrintN("Hello, world !")
 Repeat : Until Inkey() :  Macro SomeDummyMacroHere
 REBOL  [ Title:  "'Hello, World !' in 4 languages"
 CopyLeft:  "Developed in 2010 by Society" ]  Print
 "Hello, world !"  EndMacro:  func  [][]  set-modes
 system/ports/input [binary: true] Input  set-modes
 system/ports/input  [binary: false] NOP:: EndMacro
 ; Wishing to refine it with new language ? Go on !
</syntaxhighlight>
{{column}}
'''Highlighted for BASIC'''
<syntaxhighlight lang="basic">
 *BUFFER : A.A ; .( Hello, world !) @ To Including?
 Macro SkipThis; OUTPUT = Char(10) "Hello, World !"
 ;OneKeyInput  Input('Char', 1, '[-f2-q1]')  ; Char
 End; SNOBOL4 + PureBASIC + Win32Forth + REBOL = <3
 EndMacro: OpenConsole() : PrintN("Hello, world !")
 Repeat : Until Inkey() :  Macro SomeDummyMacroHere
 REBOL  [ Title:  "'Hello, World !' in 4 languages"
 CopyLeft:  "Developed in 2010 by Society" ]  Print
 "Hello, world !"  EndMacro:  func  [][]  set-modes
 system/ports/input [binary: true] Input  set-modes
 system/ports/input  [binary: false] NOP:: EndMacro
 ; Wishing to refine it with new language ? Go on !
</syntaxhighlight>
{{column}}
'''Highlighted for REBOL'''
<syntaxhighlight lang="rebol">
 *BUFFER : A.A ; .( Hello, world !) @ To Including?
 Macro SkipThis; OUTPUT = Char(10) "Hello, World !"
 ;OneKeyInput  Input('Char', 1, '[-f2-q1]')  ; Char
 End; SNOBOL4 + PureBASIC + Win32Forth + REBOL = <3
 EndMacro: OpenConsole() : PrintN("Hello, world !")
 Repeat : Until Inkey() :  Macro SomeDummyMacroHere
 REBOL  [ Title:  "'Hello, World !' in 4 languages"
 CopyLeft:  "Developed in 2010 by Society" ]  Print
 "Hello, world !"  EndMacro:  func  [][]  set-modes
 system/ports/input [binary: true] Input  set-modes
 system/ports/input  [binary: false] NOP:: EndMacro
 ; Wishing to refine it with new language ? Go on !
</syntaxhighlight>
{{columns-end}}

===DOS batch file and Perl===

The following file runs as a [[DOS]] batch file, then re-runs itself in [[Perl]]:

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'''Highlighted for DOS batch'''
<syntaxhighlight lang="dosbatch">
 @rem = ' --PERL--
 @echo off
 perl "%~dpnx0" %*
 goto endofperl
 @rem ';
 #!perl
 print "Hello, world!\n";
 __END__
 :endofperl
</syntaxhighlight>
{{column}}
'''Highlighted for Perl'''
<syntaxhighlight lang="perl">
 @rem = ' --PERL--
 @echo off
 perl "%~dpnx0" %*
 goto endofperl
 @rem ';
 #!perl
 print "Hello, world!\n";
 __END__
 :endofperl
</syntaxhighlight>
{{columns-end}}

This allows creating Perl scripts that can be run on DOS systems with minimal effort. Note that there is no requirement for a file to perform exactly the same function in the different interpreters.