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 tell it? 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 $TERM, it is set to 'screen' in screen session.. (but not 100% guaranteed)

UPDATE

alternatively, you can utilize the fact that in screen, $TERMCAP contains screen substring:

[[ $TERMCAP =~ screen ]] && echo "in screen"

also not 100% guaranteed

UPDATE2

if neither approach works, you can find some inspiration in screen manual

Answer 2

Check variable $TERM

Answer 3

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

Answer 4

I've looked at the actual source code of GNU screen. There is absolutely no way to do this for all cases.