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From: Brian Inglis <Brian DOT Inglis AT SystematicSw DOT ab DOT ca>
Subject: Re: How to query the value of %SystemDrive% in an empty environment?
Reply-To: Brian DOT Inglis AT SystematicSw DOT ab DOT ca
To: cygwin AT cygwin DOT com
References: <089bb243-1dbb-048a-39aa-f54048a39e26 AT ssi-schaefer DOT com>
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Message-ID: <0f9d219c-a9ae-237a-afcf-9dcc5a13bc01@SystematicSw.ab.ca>
Date: Tue, 6 Aug 2019 20:33:20 -0600
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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:

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

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

This email may be disturbing to some readers as it contains
too much technical detail. Reader discretion is advised.

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