Batch – how to correctly assign arbitrary percent-number (%1) or percent-asterisk (%*) arguments that may contain quotes?

Question

While working on my previous question, I faced a similar issue that I was solving initially.

Actually, I spent this month in attempts to create one universal .bat he

Answer 1

You can't solve it with normal percent expansion!
Proof:
The sample argument is "&"&.
To call a batch file with this argument, you have to escape the second ampersand.

test.bat "&"^&

It's not possible to handle this with normal commands, as you always get one unquoted ampersand.

set arg=%1
set "arg=%1"
set arg=%~1
set "arg=%~1"

Each line will fail with an error message.

Is there any command that will not fail with %1 or %*?
Yes, REM can handle them proper.

This works without erros.

REM %1

...

Funny, but how do you have any benefits from using a REM statement to get the content?
First you have to enable ECHO ON to see that it really works.

echo on
REM %1

Nice now you see the debug output

c:\temp>REM "&"&

Now you only need to redirect the debug output to a file.
There are many ways that doesn't work.

@echo on
> arg.txt REM %1
( REM %1 ) > arg.txt
call :func > arg.txt

..
:func 
REM %1

The call redirections itself works, but in the func itself you can't access the%1anymore.
But there is one solution to grab the output, with aFOR` loop

(
    @echo on
    for %%a in (42) do (
        rem %1
    ) 
) > arg.txt

Is it better to store the argument in a file instead of %1?
Yes, as a file can be read in a safe way independent of the content.

There are still some gotchas left, like /?, ^ or %%a in the argument.
But that can all be solved.

@echo off
setlocal DisableDelayedExpansion
set "prompt=X"
setlocal DisableExtensions
(
    @echo on
    for %%a in (4) do (
        rem #%1#
    ) 
) > XY.txt
@echo off
echo x
endlocal
for /F "delims=" %%a in (xy.txt) DO (
  set "param=%%a"
)
setlocal EnableDelayedExpansion
set param=!param:~7,-4!
echo param='!param!'

More about the topic at
SO:How to receive even the strangest command line parameters?
SO:Receive multiline arguments

And for Drag&Drop you need an even more complex solution SO:Drag and drop batch file for multiple files?

Edit: Solution for %*
The extensions has to be disabled, else arguments like %a--%~a will be modified.
But without extensions the %* expansion doesn't work anymore.
So the extensions are enabled just to expand the %* but before the FOR shows the content the extensions will be disabled.

@echo off
setlocal EnableExtensions DisableDelayedexpansion
set "prompt=-"
(
    setlocal DisableExtensions    
    @echo on
    for %%a in (%%a) do (
        rem # %*#
    )
) > args.tmp
@echo off
endlocal

set "args="
for /F "tokens=1* delims=#" %%G in (args.tmp) DO if not defined args set "args=%%H"
setlocal EnableDelayedExpansion
set "args=!args:~1,-4!"
echo('!args!'

This can fetch all arguments in a safe way, but for arguments from a drag&drop operations even this isn't enough, as windows have a bug (design flaw).
A file like Documents&More can't be fetched this way.