How do you tell if the current terminal session is in GNU screen?

Question

I have a command I want to execute in .bashrc only when the current terminal window is managed by GNU screen. How do I do this? Is there an environment variable for it? I used to have

if [ -n "$WINDOW" ]; then
    command
fi

But from what I can tell, $WINDOW may or may not be defined across all screen managed sessions.

Answer 1

Check for the environment variable $STY (contains info about the screen) or for $TERM being 'screen' (probably less reliable).

Answer 2

signine is correct

See the doc

http://www.gnu.org/software/screen/manual/html_node/Environment.html

STY

Alternate socket name. If screen is invoked, and the environment variable STY is set, then it creates only a window in the running screen session rather than starting a new session.