This is a script to inject environment variables into an already-running screen session. An example use case would be to set a new value for DISPLAY when you start a new X session, so that you can still start X11 programs from a shell in your screen session.
Note that any new environment variables would only take effect for
newly-spawned windows in screen. For tmux you could get creative with
a bash function that reads the output of tmux showenv and injects
the environment variables into an existing shell, but you'll still
have to do it manually.
To send the current value of $DISPLAY:
$ screen-sendenv.py DISPLAY
To send a specific value of $DISPLAY:
$ screen-sendenv.py DISPLAY=":2"