mjhjmtu

Method #1 - $DESKTOP_SESSION

I think you can find out by interrogating the environment variable $DESKTOP_SESSION. I'm not entirely positive how widely supported this is but in my limited testing it appears to be available on Fedora & Ubuntu.

$ echo $DESKTOP_SESSION
gnome

Another choice is the $XDG_SESSION_DESKTOP variable.

Method #2 - wmctrl

There is also this method that makes use of wmctrl.

$ wmctrl -m
Name: GNOME Shell
Class: N/A
PID: N/A
Window manager's "showing the desktop" mode: N/A

References

• How to determine which window manager is running

You can use this bash script. It can detect desktop environment name and version.

#!/bin/bash

function detect_gnome()

 ps -e 

function detect_kde()
 grep -m 1 'KDE' 

function detect_unity()

 ps -e 

function detect_xfce()

 ps -e 

function detect_cinnamon()
 grep -E '^.* cinnamon$' > /dev/null
 if [ $? -ne 0 ];
 then
 return 0
 fi
 VERSION=`cinnamon --version 

function detect_mate()
 grep -E '^.* mate-panel$' > /dev/null
 if [ $? -ne 0 ];
 then
 return 0
 fi
 VERSION=`mate-about --version 

function detect_lxde()

 ps -e 

function detect_sugar()

 if [ "$DESKTOP_SESSION" == "sugar" ];
 then
 VERSION=`python -c "from jarabe import config; print config.version"`
 DESKTOP="SUGAR"
 else
 return 0
 fi



DESKTOP="UNKNOWN"
if detect_unity;
then
 if detect_kde;
 then
 if detect_gnome;
 then
 if detect_xfce;
 then
 if detect_cinnamon;
 then
 if detect_mate;
 then
 if detect_lxde;
 then
 detect_sugar
 fi
 fi
 fi
 fi
 fi
 fi
fi


if [ "$1" == '-v' ];
then
 echo $VERSION
else
 if [ "$1" == '-n' ];
 then
 echo $DESKTOP
 else
 echo $DESKTOP $VERSION
 fi
fi

That probably depends on the situation. If you know which display manager is used then it may be that this one puts this information in a environment variable.

If that is not the case then I guess you have to check for every DE you want to be able to identify. All of them should introduce their own environment variables.

If the environmental variable XDG_CURRENT_DESKTOP is available, it should tell you.

# echo $XDG_CURRENT_DESKTOP
KDE

You could look for running Xorg processes. The parent of this should be your display manager. Its descendants should give an indication of what desktop environment is running. On my system, the display manager executes itself (with different parameters). This then spawns x-session-manager which is symlinked to xfce4-session. This may be enough, but all the children of this are related to my desktop environment. Finding them via the process tree should be the best way to exclude elements of other window systems started by various programs (or perhaps deliberately).

My first thought was that it would be be best to look for the window manager associated with your desktop environment, but often a different one can be configured to run (eg xmonad in Gnome) so this is not robust. The best one to look for is probably the one which manages the actual desktop, eg xfdesktop or whatever element of the desktop environment you actally need for your script to work :)

Example

Here is an example using procps-ng (-C and --ppid are not POSIX). It assumes the is only one instance of Xorg.

This is just an example that works for the xfce desktop. A full working example requires an investigation in to the processes that each desktop system uses, just as most of the other solutions require investigation into how environmental variables are set in various other desktop systems.

X=Xorg

search_descendants ()
another_desktop_process)$' &&
 return 0

 for pid in $(ps h -o pid --ppid $1)
 do
 search_descendants $pid && return 0
 done

 return 1


dm_pid=$(ps h -o ppid -C "$X")

case "$(search_descendants $dm_pid)" in
 xfdesktop)
 desktop=xfce
 ;;
 another_desktop_process)
 desktop=another_desktop
 ;;
 *)
 desktop=unknown
 ;;
esac

echo $desktop

From all the experimenting reported in the numerous comments, I think its my duty as the OP to come up with a consensus answer. (Rest assured, I would be happy to review this answer should contrasting data become available.)

For now, it seems best to take our lead from $XDG_CURRENT_DESKTOP when this variable is defined. If not, $XDG_DATA_DIRS may provide the desired information, more so than the first letter of $DESKTOP_SESSION:0:1.

This works on both Ubuntu 18.10 (cosmic) [lxqt type] and Mint 19 (tara) [cinnamon type]:

$ set | grep XDG_CURRENT_DESKTOP | tr '[:upper:]' '[:lower:]' | cut -d'=' -f2

Capture the result into a variable, and execute further necessary code via capable analytic logic (case stmt, if/then) which includes any/all recognized types from there; and/or function gracefully when unrecognized types are in use.