How to detect availability of GUI in Bash/Shell?

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I'm writing a CLI in NodeJS. As I can easily run bash/shell commands using the child_process, I'd like to know the easiest most cross platform way to detect GUI availability in bash/shell.

Thanks!

On macOS, there's not a clearly appropriate way to check this from a shell, as such. There's a programmatic way, and we can use an interpreted language to take advantage of that.

Here's a little script that outputs one of three states, Mac GUI, Mac non-GUI, or X11:

#!/bin/bash
if [ `uname` = "Darwin" ]
then
    if which swift >/dev/null && swift <(cat <<"EOF"
import Security
var attrs = SessionAttributeBits(rawValue:0)
let result = SessionGetInfo(callerSecuritySession, nil, &attrs)
exit((result == 0 && attrs.contains(.sessionHasGraphicAccess)) ? 0 : 1)
EOF
)
    then
        echo "Mac GUI session"
    elif [ -n "$DISPLAY" ]
    then
        echo "Mac X11 GUI session"
    else
        echo "Mac non-GUI session"
    fi
elif [ -n "$DISPLAY" ]
then
    echo "X11 GUI session"
fi

Macs can have an X server installed, in which case DISPLAY is defined. However, I don't know if your Electron app will work properly in that configuration. So, I detected it separately.

how to detect availability of GUI, For Linux: I have a text mode installation (bash) script and a graphical mode setup program (a Free Pascal binary). I'd like to run the graphical setup when a GUI� The if command checks the exit code of the following command (the ping). If the exit code is zero (which means that the command exited successfully) the then block will be executed. If it return a non-zero exit code, then the else block will be executed.

Check if DISPLAY is set in the environment. If it is, you have an Xserver running. If not, you don't. Pretty sure that wayland sets it too.

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Here is a working example:

if [ x$DISPLAY != x ] ; then
  echo "GUI Enabled"

else
  echo "GUI Disabled"

fi

All this does is checks the $DISPLAY variable.

16 Linux server monitoring commands you should know | HPE, That's because Linux GUIs take up system resources that could be better used elsewhere. turn off the GUI and use these tools from the Linux command shell. For day-to-day server monitoring, I find nmon to be the single most useful Corporate Responsibility Global Diversity & Inclusion Supply Chain� The system I'm working on is quite minimal, all I can see are xterm windows, from where I can open applications (in separate windows). I can open new xterm window by right click in a free area on the desktop.

Try this : echo $XDG_CURRENT_DESKTOP Or this : echo $DESKTOP_SESSION

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Comments
  • If you're writing a CLI, why do you need GUI availability?
  • Because I want to launch an alternative electron app if GUI is available, it's fency :D
  • Probably checking for existence of the environment variable DISPLAY is the best bet. Not sure it's 100% reliable check on MacOS, though.
  • Indeed, the DISPLAY variable does not exist on OSX :/
  • Just launch your app. If there is a GUI, it will run. If not, it will fail in a predictable way. If you detect that predictable way, move into CLI operation - otherwise fail in error?
  • Why swift <(cat <<"EOF" instead of swift - <<"EOF"?
  • @CharlesDuffy If it receives its input from stdin rather than a filename argument, it behaves as though it's interactive and exits with 0 status regardless of what's passed to exit(). Also, it produces annoying extraneous output.
  • I wonder if we have different releases. swift - <<<'import Security; exit(3)'; echo $? emits no output at all (prior to the echo) and shows exit status 3 for me -- that's with Apple Swift version 4.2.1 (swiftlang-1000.11.42 clang-1000.11.45.1)
  • ...or perhaps the behavior you mention above is without the explicit - specifying stdin?
  • Yeah, the explicit - seems to make the difference. For the record, I'm currently testing on Sierra with Xcode 8, so: Apple Swift version 3.1 (swiftlang-802.0.51 clang-802.0.41).
  • He tagged it as MacOS as well. Not sure DISPLAY will be set unless Xquartz is installed.
  • I missed that. I'm not sure, either.