Running xprop _NET_WM_PID from a terminal will put X into a special mode where you can click on a window to get that window's PID in the terminal.

Then run ls -l /proc/<pid>/exe and look at where the link is to to figure out what the program's file name is.

The following is a little python script take from a program I'm working on:

#! /usr/bin/env python



import os, subprocess



# Function based on code from apport

def get_window_pid():

    xprop = subprocess.Popen(['xprop', '_NET_WM_PID'],

            stdout=subprocess.PIPE, stderr=subprocess.PIPE)

    (out, err) = xprop.communicate()

    if xprop.returncode == 0:

        try:

            return int(out.split()[-1])

        except ValueError:

            return -1

    else:

        return -1



def get_window_exe():

    pid = get_window_pid()

    

    if pid == -1:

        return ''

        

    return os.path.realpath('/proc/' + str(pid) + '/exe')



if __name__=='__main__':

    exe = get_window_exe()

    if exe == '':

        print 'Unable to identify window's executable' 

    else:

        print exe

Save this into a file and run by typing python <filename>.py. Click on the window and it will print the program's name.