4

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
]
Jeff Schaller
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user279540
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3 Answers3

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.

Kusalananda
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user279540
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    Actually it won't necessarily be ":0", but it will be something; so the usual idiom is if [[ -n "$DISPLAY" ]]; then. (The construction [[ -n "$DISPLAY" ]] checks for a string of length greater than zero.) – AlexP Jun 24 '18 at 00:47
  • I see, thank you very much for clarifying. – user279540 Jun 24 '18 at 01:09
  • ... and is subject to a false positive , as a tty login could set it. – Jeff Schaller Jun 24 '18 at 03:23
  • it could be missing as entirely, btw, even in X session. – ILMostro_7 Jun 24 '18 at 03:27
  • Does my edit fix it?...I am interested in why it won't always work as when I had tested it in my linux machine, it had worked as anticipated...thanks~ – user279540 Jun 24 '18 at 04:05
  • It could be given a different value, if say, someone wanted to run a (your) program in CLI/TUI mode instead of GUI mode, or if they wanted to run it on a X server when at a console. But those are valid use cases that you should be prepared for. – Ignacio Vazquez-Abrams Jun 24 '18 at 04:09
  • It had been working when I started my X server through startx through the console. I don't use a display manager so I frequently switch between my X applications and console. I wanted different behavior depending on whether I was in a graphical environment or not. Somehow before it rendered different behavior inside and outside of console. I am still wondering if I have implemented this correctly and what is the behavior that I should expect out of $DISPLAY. – user279540 Jun 24 '18 at 04:16
2

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.

Jeff Schaller
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0

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"
ctac_
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