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From: "David Allsopp" <dra27@cantab.net>
To: "'Marco Atzeri'" <marco.atzeri@gmail.com>, <cygwin@cygwin.com>
References: <005c01d1a6e2$30270ba0$907522e0$@metastack.com> <CACoZoo1LObZ0zu9X5O6dV4cO4jN+GO28bdRbuDkTMdaKHXpVbQ@mail.gmail.com> <000101d1a76d$c37c6b80$4a754280$@metastack.com> <967954968.20160506172040@yandex.ru> <006301d1a834$6ccd1380$46673a80$@cantab.net> <6e1f2ba2-0c8e-4659-4c5a-d748e90c1ced@lysator.liu.se> <8d8fe966-caeb-491c-32e7-fc48ccd56d74@gmail.com> <008f01d1aa0a$6b163f30$4142bd90$@cantab.net> <21af49f2-f685-828c-6bd4-8d734eedf378@gmail.com>
In-Reply-To: <21af49f2-f685-828c-6bd4-8d734eedf378@gmail.com>
Subject: RE: Formatting command line arguments when starting a Cygwin process from a native process
Date: Mon, 9 May 2016 17:14:29 +0100
Message-ID: <009001d1aa0d$de667b50$9b3371f0$@cantab.net>
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Marco Atzeri wrote:
> On 09/05/2016 17:49, David Allsopp wrote:
> > Marco Atzeri wrote:
> >>
> >> Ultimate overview of MS escape howto :
> >>
> >> https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04
> >> /23/e veryone-quotes-command-line-arguments-the-wrong-way/
> >
> > This is a great article (which I'd not come across before), but this
> > relates to Microsoft's mechanisms for quoting which aren't applicable
> > here - it's definitely the Cygwin DLL which does it!
> >
> >
> > David
> >
> 
> Hi David,

Hi!

> I am puzzled, I had the impression you asked:
> "I am trying to work out the precise details for character escaping when
> starting a Cygwin process from a native (i.e. non-Cygwin) Windows
> process."
> 
> So the exec should be on "Windows process" side, why inside the Cygwin DLL
> ?

In Windows, there is no "exec" - the equivalent functions in Microsoft's C
runtime are themselves emulations boiling down to a CreateProcess call
(unlike on Unix, where the exec family are actual system calls). That
CreateProcess call takes exactly a single string for the entire command line
which the Cygwin DLL then has to convert to argc/argv in order to call the
main function in the Cygwin program started (Microsoft's C runtime has to do
the same thing which is part of what that blog explains). Any sane native
Windows program will use (or be compliant with) CommandLineToArgvW, but no
program has to do it that on Windows (indeed, Cygwin takes "advantage" of
this to do its own thing).

I have total control of my native call to CreateProcess, so it's definitely
about working out exactly what Cygwin does with the command line. AFAICT,
when a Cygwin program execs another Cygwin program, they actually
communicate argc and argv via memory, rather than through the process
invocation (although I'm really not sure that I've interpreted that
correctly) which is why this doesn't come up in pure Cygwin-land.

I think I'm there, it's just not as clean (or documented) as might be nice!


David


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