How to use groups from the command line (or at all)?

[Tim Landscheidt]

Hi,

background: I use Screen 4.09.00 to control Emacs either in
a local GUI terminal or an SSH client from my phone by using
a command à la:

| screen -dRS emacs_gnus sh -c 'pidof emacs || emacs -nw -f gnus'

I want to customize Emacs's browse-url et al. so that they
do the Right Thing™ depending on which device I'm controll-
ing Emacs from.  My current game plan is to enhance the com-
mand above so that prior to executing Screen, it notes the
controlling device in some file /var/run/user/…  that I can
then read in Emacs and act upon its contents.  But it would
be more appropriate and better reusable code to consider
this information a "property" of the Screen session.  Look-
ing at the Screen manual, at first I thought I might store
the information in a register, but groups ("local", "de-
vice1", "device2", etc.) appear to be more fitting.

So I launch a test session:

| $ screen -dRS test

and, in another terminal, I try to assign the session to a
group and (unsuccessfully) query its name:

| $ screen -S test -X group local
| $ screen -S test -X group
| $

Rereading the manual, I note that it says: "Once a new group
is created, it will act as a container for windows and even
other groups."  So I assume that I need to create the group
before using it:

| $ screen -S test -X screen -t local //group
| $

This causes the "test" session to show a screen with the
title "Group: local" and leaves me without a clue how to re-
turn to my shell prompt.  But even though it did something,
it did not succeed to assign the session to something query-
able from the command line:

| $ screen -S test -X group local
| $ screen -S test -X group
| $ screen -S test -ls
| There is a screen on:
|         64047.test      (Attached)
| 1 Socket in /run/screen/S-tim.
| $

So (how) can I create a group, assign a session to it, and
query the group a session is assigned to?

TIA,
Tim