Bash script that reports the currently set KDE Plasma wallpaper, on the specified (or current) activity and screen. Supports the Image and Slideshow plugins and can complain correctly about the POTD plugin.

read-plasma-wallpaper

#!/bin/bash

##
# Helper to find the user configured name of an activity, by its ID
function getActivityName() {
  qdbus org.kde.ActivityManager /ActivityManager/Activities \
    org.kde.ActivityManager.Activities.ActivityName "$1"
}

##
# Helper to list all the currently configured activities by their ID
function listActivityIds() {
  qdbus org.kde.ActivityManager /ActivityManager/Activities \
    org.kde.ActivityManager.Activities.ListActivities
}

##
# Helper to get the ID of the current activity
function currentActivity() {
  qdbus org.kde.ActivityManager /ActivityManager/Activities \
    org.kde.ActivityManager.Activities.CurrentActivity
}

activity="$1" ## allow the user to choose the activity to look at
screen="${2:-0}" ## allow the user to choose the screen to look at
# but default to the first screen, if they didn't specify

grep -qi plasma <<<"$DESKTOP_SESSION" || { echo "Not running under a Plasma desktop!">&2; exit 1; }

# if the user did not specify an activity, use the current one
[ -z "$activity" ] && activity=$(currentActivity)

# if the user specified the activity by name, locate the ID
if [ -z "$(getActivityName "$activity")" ]; then
	activities=( $(listActivityIds) )
	aname="$activity"
	activity=
	for aid in "${activities[@]}"; do
		if [ "$aname" == "$(getActivityName $aid)" ]; then
			activity=$aid
		fi
	done
fi

[ -z "$activity" ] && { echo "Activity '$activity' was not found!">&2; exit 1; }

# The meat of the thing - ask Plasma to run our script
qdbus org.kde.plasmashell /PlasmaShell org.kde.PlasmaShell.evaluateScript "
  var actId = '$activity';
  var scr = $screen;
  var ds = desktops(); // load the containments
  for (let d of ds) { // and walk through them
    // skip any containment that does not match activity and screen
    if (d.readConfig('activityId') != actId ||
        d.readConfig('lastScreen') != scr)
      continue;
    // prepare to read the General configuration (where plugins normally
    // put the current image)
    d.currentConfigGroup = Array('Wallpaper',d.wallpaperPlugin,'General');
    // identify the wallpaper plugin so we can read it properly
    if (d.wallpaperPlugin == 'org.kde.slideshow') {
      print(d.readConfig('Image').replace('file://',''));
    } else if (d.wallpaperPlugin == 'org.kde.image') {
      print(d.readConfig('Image').replace('file://',''));
    } else if (d.wallpaperPlugin == 'org.kde.potd') {
      print('Picture of the Day (Provider: ' + d.readConfig('Provider') +
          ') does not support reading the current image');
    } else {
      print('Unsupported wallpaper plugin: '+d.wallpaperPlugin+'\n');
    }
    break;
  }"