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Subject:	Re: PATHEXT is fundamental to Windows and Should be recognised by CYGWIN
To:	cygwin AT cygwin DOT com
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From:	cyg Simple <cygsimple AT gmail DOT com>
Message-ID:	<8dc84987-802d-30d3-3ebb-2ba25871b561@gmail.com>
Date:	Tue, 9 Aug 2016 08:58:55 -0400
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On 8/8/2016 10:33 AM, Corinna Vinschen wrote:
> On Aug  8 09:43, cyg Simple wrote:
>> As for PATHEXT we can do the following scenario instead.
>>
>> export PATHEXT="$PATHEXT;.TXT"
>> vi foo.txt
>> :set ff=dos
>> i
>> a
>> b
>> c
>> <ESC>
>> :wq
>> cmd /c foo
> 
> As you show here, the PATHEXT definition is so that it also contains
> file suffixes which require to know the interpreters starting them.  To
> implement that, the lib would have to either read the registry to know
> the connection between suffix and interpreter (which is pretty
> convoluted), or it would have to "start the file", aka call ShellExecute
> on the file, without knowing what process will come up as child process.
> In your example that would be Notepad or Write.
> 
> The way this works is just not feasible to be used from inside the DLL,
> e.g.:
> 
> - ShellExecute does not return a handle to the called process, so the
>   parent can't wait(2) for it.
> 
> - ShellExecute does not allow to specify an environment for the child
>   process.  Cygwin's Windows environment is reduced to minimal size.
>   Cygwin children inherit the POSIX environment by a simple copy
>   process.  Only when starting a non-Cygwin process, this process gets
>   a full Windows environment by means of the matching CreateProcess
>   parameter.
> 

Sorry, it seems I confused the issue.  I was suggesting with this
example that as a Cygwin shell user I could use this technique to start
a file if I so choose without any modification to Cygwin.

> So, if we actually implement PATHEXT, its usage would be limited to
> suffixes of binary files and files starting with #!<interpreter>, or we
> would have to use a way to start an application which doesn't work well
> in a POSIX scenario, or we would have to search the registry for the
> suffix linkage.  Additionally to searching a variable number of files
> for each single file access.

I tried "chmod +x foo.txt; ./foo.txt" but that results in Cygwin
assuming the text file is a script and executing each line of the file.
If PATHEXT were used only to determine that the file should be passed to
ShellExecute instead it might be beneficial but since I can easily just
do "cmd /c foo.txt" then probably not so much.

> 
> Additionally I would (again?) like to stress that PATHEXT is a feature
> of CMD, aka, the shell.  It's not a feature of the underlying libs.

And other application type programs and libraries.  WSH for one makes
use of PATHEXT.
https://msdn.microsoft.com/en-us/library/fd7hxfdd(v=vs.84).aspx

-- 
cyg Simple

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