How to check if the current shell session is in the gui or the tty

Question

Which environment setting in the zsh shell will allow me to find whether I am in the x-server or if I am in the console? I am trying to find a way to implement having different setting in my .zshrc for whenever I am in my terminal emulator and whenever I am in my tty/console.

Basically I will have,

(pseudocode)

if(current shell session is in console)
[
    implement PROMPT x
]else[
    implement PROMPT Y
] 

Answer 1

I think it would be more straightforward to check if the current tty is named like the local consoles:

case $(tty) in 
  (/dev/tty[1-9]) PS1='console version';; 
              (*) PS1='not console version';; 
esac

That's just one way to check the result; you could use grep or parameter expansion, but it shows the idea.

You could additionally check $DISPLAY, but that's not a guarantee, and I can't imagine what you would be doing in a shell prompt that would require an X11 environment.

Answer 2

Thanks to @Ignacio Vazquez-Abrams and @Jeff Schaller (and other commenters below), I realized that $DISPLAY was the enviormental variable I needed. If you are in a display server the value held by $DISPLAY will be 0 will be returned (as something). Hence, the following code (should?) works--

if [[ -n $DISPLAY ]];
then
    PROMPT = (etc)
else 
    PROMPT = (etc2)
fi

Thanks to all.

Answer 3

When you work on console, you first login.
So if you look for login, you can know where you are.

You can try this :

[ "$(ps -t $(ps -o comm= -o tty= | \
awk '$1=="ps"{print $2}') | \
grep [l]ogin)" ] && \
echo "console" || echo "terminal"