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From: "David Allsopp" <dra-news AT metastack DOT com>
To: <cygwin AT cygwin DOT com>
References: <005c01d1a6e2$30270ba0$907522e0$@metastack.com> <CACoZoo1LObZ0zu9X5O6dV4cO4jN+GO28bdRbuDkTMdaKHXpVbQ AT mail DOT gmail DOT com>
In-Reply-To: <CACoZoo1LObZ0zu9X5O6dV4cO4jN+GO28bdRbuDkTMdaKHXpVbQ@mail.gmail.com>
Subject: RE: Formatting command line arguments when starting a Cygwin process from a native process
Date: Fri, 6 May 2016 10:03:22 +0200
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[With apologies if threading is broken; I erroneously thought as the list was not subscriber-only that replies would use reply-all and so wasn't subscribed]

On Thu, May 5, 2016 at 06:47 PM, Erik Soderquist wrote:
> On Thu, May 5, 2016 at 11:24 AM, David Allsopp wrote:
> >
> > 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.
> <snip>
> > For example:
> >
> >   argv[0] = "foo"
> >   argv[1] = "bar baz"
> >
> > then the resulting command line string should be:
> >
> >   lpCommandLine = "foo bar\" \"baz"
> 
> If I recall correctly, Windows cmd.exe uses the carrot (^) as the general
> escape from shell character, so
> 
> C:\cygwin64\bin>.\echo.exe -e ^"hello\nworld^"	
> hello
> world
> 
> works.

Indeed - but I'm not using cmd, or any shell for that matter (that's actually the point) - I am in a native Win32 process invoking a Cygwin process directly using the Windows API's CreateProcess call. As it happens, the program I have already has the arguments for the Cygwin process in an array, but Windows internally requires a single command line string (which is not in any related to Cmd).

> However, I've found Windows's interpretation to be inconsistent, so often
> have to play with it to find what the "right combination" is for a
> particular instance.
> 
> I find echoing the parameters to a temporary text file and then using the
> file as input to be more reliable and easier to troubleshoot, and it
> breaks apart whether it is Windows cli inconsistencies or receiving
> program issues very nicely with the text file content as an intermediary

This is an OK tack, but I don't wish to do this by experimentation and get caught out later by a case I didn't think of, so what I'm trying to determine is *exactly* how the Cygwin DLL processes the command line via its source code so that I can present it with my argv array converted to a single command line and be certain that the Cygwin will recover the same argv DLL.

My reading of the relevant sources suggests that with globbing disabled, backslash escape sequences are *never* interpreted (since the quote function returns early - dcrt0.cc, line 171). If there is no way of encoding the double quote character, then perhaps I have to run with globbing enabled but ensure that the globify function will never actually expand anything - but as that's a lot of work, I was wondering if I was missing something with the simpler "noglob" case.


David


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