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From: Andrew Schulman <schulman.andrew@epa.gov>
Subject: Re: Change PS1 when run as administrator
Date: Tue, 15 Mar 2016 12:33:32 -0400
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> I just came up with this recipe to change the default PS1 value to use red for the user@host part of the prompt and to change the $ character to a #:
> 
>     if id | grep -qi 'member of administrators group'
>     then
>         export PS1=$(echo "$PS1" | sed -e 's_32_31_' -e 's_\\\$_#_')
>     fi
> 
> I’m not certain the string match on the output of id(1) works everywhere.  Is there a better way to check for admin privileges under Cygwin?  You can’t check for UID or EUID == 0, for example, as you’d do on a true POSIX system.

Ha!  Yes, there is:  see
https://cygwin.com/ml/cygwin/2015-02/msg00057.html.  The magic test is

id -G | grep -qE '\<(544|0)\>'

where 544 is the Administrators group, and 0 is the root group in case the
old root group entry is present in /etc/group.

For example:

id -G | grep -qE '\<(544|0)\>' && echo admin || echo user


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