A combination of wmctrl and xprop offers many possibilities.

Example 1:

running_gui_apps() {



    # loop through all open windows (ids)

    for win_id in $( wmctrl -l | cut -d' ' -f1 ); do 



        # test if window is a normal window

        if  $( xprop -id $win_id _NET_WM_WINDOW_TYPE | grep -q _NET_WM_WINDOW_TYPE_NORMAL ) ; then 



            echo "$( xprop -id $win_id WM_CLASS | cut -d" " -f4- )"", window id: $win_id"



        fi



    done

}

The output could look in this case similar like this:

"Firefox", window id: 0x032000a9

"Gnome-terminal", window id: 0x03a0000c

"Thunar", window id: 0x03600004

"Geany", window id: 0x03c00003

"Thunar", window id: 0x0360223e

"Mousepad", window id: 0x02c00003

"Mousepad", window id: 0x02c00248

"Xfce4-terminal", window id: 0x03e00004

Example 2:

running_gui_apps() {

    applications=()



    # loop through all open windows (ids)

    for win_id in $( wmctrl -l | cut -d' ' -f1 ); do 



        # test if window is a normal window

        if  $( xprop -id $win_id _NET_WM_WINDOW_TYPE | grep -q _NET_WM_WINDOW_TYPE_NORMAL ) ; then 



            # filter application name and remove double-quote at beginning and end

            appname=$( xprop -id $win_id WM_CLASS | cut -d" " -f4 )

            appname=${appname#?}

            appname=${appname%?}



            # add to result list

            applications+=( "$appname" ) 



        fi



    done



    # sort result list and remove duplicates  

    readarray -t applications < <(printf '%s0' "${applications[@]}" | sort -z | xargs -0n1 | uniq)



    printf -- '%s

' "${applications[@]}" 

}

Output example:

Firefox

Geany

Gnome-terminal

Mousepad

Thunar

Xfce4-terminal

You can add the function to your ~/.bashrc or run it from an script file.