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Date: Mon, 22 Apr 2024 10:54:33 +0200
To: cygwin AT cygwin DOT com
Subject: Re: /usr/bin/sg in Cygwin?
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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Cc: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
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On Apr 22 07:55, Cedric Blancher via Cygwin wrote:
> On Mon, 22 Apr 2024 at 01:20, Dan Shelton via Cygwin <cygwin AT cygwin DOT com> wrote:
> >
> > On Sat, 20 Apr 2024 at 07:39, Brian Inglis via Cygwin <cygwin AT cygwin DOT com> wrote:
> > >
> > > On 2024-04-19 17:47, Dan Shelton via Cygwin wrote:
> > > > On Fri, 23 Feb 2024 at 22:25, Dan Shelton wrote:
> > > >> Is there a package which provides /usr/bin/sg (execute shell commands
> > > >> in a different group)?
> > >
> > > The POSIX standard command is newgrp - install cygwin-doc to see Cygwin (and
> > > newlib libc) man pages (and info, html, PDF docs), man-pages-posix to see POSIX
> > > man pages, and man-pages-linux if you want to see recent Linux release man pages.
> > >
> > > To see possibly relevant commands, run:
> > >
> > > $ apropos -s 1,1p group
> > > chgrp (1)            - change group ownership
> > > chgrp (1p)           - change the file group ownership
> > > chown (1)            - change file owner and group
> > > g3topbm (1)          - convert a Group 3 fax file into a PBM image
> > > groups (1)           - print the groups a user is in
> > > id (1)               - print real and effective user and group IDs
> > > make (1)             - GNU Make utility to maintain groups of programs
> > > make (1p)            - maintain, update, and regenerate groups of programs
> > > mkgroup (1)          - Write /etc/group-like output to stdout
> > > newgrp (1)           - change primary group for a command
> > > newgrp (1p)          - change to a new group
> > > pbmtog3 (1)          - convert a PBM image into a Group 3 MH fax file
> >
> > newgrp(1) is USELESS. It only opens an interactive shell, but does not
> > allow the user to execute a non-interactive script with the requested
> > group like bash -c does.
> 
> Linux /usr/bin/sg source is in
> https://github.com/shadow-maint/shadow/blob/master/src/newgrp.c
> So this is just a packaging issue that whoever does the Cygwin newgrp
> package has to package /usr/bin/sg too

newgrp(1) is a Cygwin util from the base package:

  $ cygcheck -f /usr/bin/newgrp
  cygwin-3.6.0-0.109.ga0a25849f9dd

Reason being that the functionality under Windows is pretty limited
compared to "real" POSIX systems...

https://cygwin.com/cygwin-ug-net/newgrp.html

...and fetching the default environment of the user (to implement the
dash option '-') is pretty different from any other known POSIX system,
having to use Windows functions:

  https://cygwin.com/cgit/newlib-cygwin/tree/winsup/utils/newgrp.c

If anybody thinks he or she can provide a useful shadow-utils
package, feel free.  But it might not be worth the effort, probably.


Corinna

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