list client applications running on a display
xlsclients [-display displayname] [-a] [-l] [-m maxcmdlen] [-version]
Xlsclients is a utility for listing information about the client appli‐ cations running on a display. It may be used to generate scripts rep‐ resenting a snapshot of the user's current session.
-display displayname This option specifies the X server to contact. -a This option indicates that clients on all screens should be listed. By default, only those clients on the default screen are listed. -l List in long format, giving the window name, icon name, and class hints in addition to the machine name and command string shown in the default format. -m maxcmdlen This option specifies the maximum number of characters in a command to print out. The default is 10000. -version Print the program version and exit.
DISPLAY To get the default host, display number, and screen.
Jim Fulton, MIT X Consortium