XSCHEM embeds a tcl shell, when running xschem the terminal will present a tcl prompt allowing to send / get commands through it. Most user actions done in the drawing window can be done by sending tcl commands through the tcl shell. Since I/O is simply done through stdin/stdout this allows XSCHEM to be controlled by another application, by piping XSCHEM commands to XSCHEM stdin and getting XSCHEM answers piped from XSCHEM stdout.

XSCHEM implements a TCL xschem command that accepts additional arguments. This command implements all the XSCHEM remote interface. Of course all Tck-Tk commands are available, for example, if this command is sent to XSCHEM: 'wm withdraw .' the xschem main window will be withdrawn by the window manager, while 'wm state . normal' will show again the window.
This command: 'puts $XSCHEM_LIBRARY_PATH' will print the content of the XSCHEM_LIBRARY_PATH tcl variable containing the search path.