yaauie/hello.jscript.bat

## hello.jscript.bat
0</* :hello
@ECHO Hello, batch!
@cscript /nologo /E:jscript %~f0 %*
@goto :EOF
*/0;
WScript.Echo('Hello, jscript!');

## hello.jscript.output
Hello, batch!
Hello, jscript!

## hello.jscript.readme.md

      
    Raw
  

              hello.jscript.readme.md
            
          
    Windows lacks anything quite like Unix's shebang, which provides a way for
a script to tell its interpreter how to interpret it, but polyglots can be
used to provide similar functionality.
A polyglot is a script that works in multiple interpreters, hiding
functionality and syntax specific to one language from another language's
interpreter by clever use of each language/interpreter's specific features.
Let's look at how each of our two interpreters deal with the above script:


BATCH allows redirection to occur anywhere in a command line, not just a
the tail. It does this by actually rearranging the command in pre-parsing,
turning our first line 0<*/ :hello into :hello 0<*/, which is a label
and is not executed. Line 2 is a hello from batch, Line 3 executes the
called script in cscript with the appropriate arguments (subtitute your
interpreter here), and line 4 sends us to :EOF, ignoring the rest of the
script.


JAVASCRIPT: Lines 1-5 are reduced to a single instruction once the
multi-line comment is ignored: 0<0;. This adds minimal weight and no
memory overhead, and the script continues as normal.
	0</* :hello
	@ECHO Hello, batch!
	@cscript /nologo /E:jscript %~f0 %*
	@goto :EOF
	*/0;
	WScript.Echo('Hello, jscript!');