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Date:	Wed, 7 Aug 2019 13:19:43 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	Michael Haubenwallner <michael DOT haubenwallner AT ssi-schaefer DOT com>
Cc:	cygwin AT cygwin DOT com
Subject:	Re: How to query the value of %SystemDrive% in an empty environment?
Message-ID:	<20190807111943.GC11632@calimero.vinschen.de>
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On Aug  7 13:08, Michael Haubenwallner wrote:
> 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 WIND=
IR
> >> environment variables are preserved (or recreated):
> >>  $ /usr/bin/env -i /usr/bin/env
> >>  SYSTEMROOT=3DC:\Windows
> >>  WINDIR=3DC:\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 "System=
Drive"
> >> environment variable.
> >> The problem behind is that I'm using "vswhere.exe" to locate some Visu=
al Studio
> >> environment from within some scripts run via 'env -i', causing vswhere=
.exe to
> >> create a directory named "%SystemDrive%" in the current working direct=
ory:
> >> So I better ensure the SystemDrive environment variable is set for vsw=
here.exe.
> >> Any ideas?
> >=20
> > There is a reg entry:
> >=20
> > $ head
> > /proc/registry/HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control/Syst=
emBootDevice;
> > echo
> > multi(0)disk(0)rdisk(1)partition(3)
> >=20
> > but how do you convert that to a device letter?
> >=20
> > SYSTEMDRIVE is a dynamic env var created at startup pointing to the boo=
t drive
> > letter. It is not instantiated anywhere else as far I could find. A num=
ber of
> > low level reg entries use that env var. Only option is to pass it throu=
gh:
>=20
> Heck, even CreateEnvironmentBlock() relies on SYSTEMROOT env var being se=
t,
> otherwise returning things like ProgramData=3D"%SystemDrive%\ProgramData".

So, what does this have to do with Cygwin in case you clean out the
environment?  This is nothing you want to do if you plan to start
a non-Cygwin executable.


Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

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