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Subject: Re: How to query the value of %SystemDrive% in an empty environment?
To: cygwin AT cygwin DOT com
References: <089bb243-1dbb-048a-39aa-f54048a39e26 AT ssi-schaefer DOT com> <0f9d219c-a9ae-237a-afcf-9dcc5a13bc01 AT SystematicSw DOT ab DOT ca>
From: Michael Haubenwallner <michael DOT haubenwallner AT ssi-schaefer DOT com>
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Date: Wed, 7 Aug 2019 13:08:51 +0200
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On 8/7/19 4:33 AM, Brian Inglis wrote:
> On 2019-08-06 09:20, Michael Haubenwallner wrote:
>> using 'env -i' to create an empty environment, the SYSTEMROOT and WINDIR
>> environment variables are preserved (or recreated):
>>  $ /usr/bin/env -i /usr/bin/env
>>  SYSTEMROOT=C:\Windows
>>  WINDIR=C:\Windows
>> And with cygpath, there is the -A, -D, -H, -O, -P, -S, -W and even -F flags
>> to query the values for various directories.
>> Now what I've failed to find is how to query the value for the "SystemDrive"
>> environment variable.
>> The problem behind is that I'm using "vswhere.exe" to locate some Visual Studio
>> environment from within some scripts run via 'env -i', causing vswhere.exe to
>> create a directory named "%SystemDrive%" in the current working directory:
>> So I better ensure the SystemDrive environment variable is set for vswhere.exe.
>> Any ideas?
> 
> There is a reg entry:
> 
> $ head
> /proc/registry/HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control/SystemBootDevice;
> echo
> multi(0)disk(0)rdisk(1)partition(3)
> 
> but how do you convert that to a device letter?
> 
> SYSTEMDRIVE is a dynamic env var created at startup pointing to the boot drive
> letter. It is not instantiated anywhere else as far I could find. A number of
> low level reg entries use that env var. Only option is to pass it through:

Heck, even CreateEnvironmentBlock() relies on SYSTEMROOT env var being set,
otherwise returning things like ProgramData="%SystemDrive%\ProgramData".

> 
> $ /usr/bin/env -i SYSTEMDRIVE="$SYSTEMDRIVE" /usr/bin/env
> SYSTEMDRIVE=C:
> SYSTEMROOT=C:\WINDOWS
> WINDIR=C:\WINDOWS

Feels like the Cygwin DLL better should try to keep SYSTEMDRIVE being set, no?

/haubi/ (about to prepare some patch)

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