Extended Tcl has:
The following global variables are set and/or used by the Tcl shell (not to be confused with tclsh).
Contains the name of the Tcl program specified on the command line or the name that the Tcl shell was invoked under if no program was specified. argc Contains a count of the number of argv arguments (0 if none).
A list containing the arguments passed in from the command line, excluding arguments used by the Tcl shell. The first element is the first passed argument, not the program name.
Set to 1 if Tcl shell is invoked interactively, or 0 if the Tcl shell is directly executing a script. Normally checked by scripts so that they can function as a standalone application if specified on the command line, but merely load in and not execute if loaded during an interactive invocation of Tcl.
Path to search to locate Tcl autoload libraries. Used by the both the Tcl and TclX library autoloading facility.
Path to the TclX runtime library. If your running the TclX shell or an application based on it (like wishx). The TclX initialization file normally adds this to the auto_path.
Path to the TkX runtime library. This is set only if your application has called Tkx_Init. The TkX initialization file normally adds this to the auto_path.
Contains code to run to output the prompt used when interactively prompting for commands.
Contains code to run to output the prompt used when interactively prompting for continuation of an incomplete command.
Array that contains information used internally by various Tcl procedures that are part of the TclX shell.