This global variable is provided by tclsh and wish. It gives you the arguments the app was called with as a list, similar to C's argv, but without the app name itself (you get that in ''::[argv0]''). We don't need ''argc'' as we can always determine [[llength $argv]]. 

'''DGP''' -- It is true that we do not need ''::argc'', but
'''tclsh''' and '''wish''' and any application embedding Tcl
that calls ''Tcl_Main()'' provide it anyway.

argv0 describes the name of the top-level script that was invoked via tclsh or wish.

http://purl.org/tcl/home/man/tcl8.3.2/UserCmd/tclsh.htm

http://purl.org/tcl/home/man/tcl8.3.2/UserCmd/wish.htm

See [command options] for a discussion of various options one has
in parsing the argv (and argv-like) information.

Also, note that [[[info] script]] describes the name of the currently executing script and this name even gets set by [source].  ''::argc Technically, it is set by Tcl_EvalFile(), for those using the Tcl C API.''

'''Technically, it's set by Tcl_EvalFile(), for those using Tcl's C API.'''

The command [[[info] nameofexecutable]] describes the name of the executing binary, and might be thought more like the C level argv[[0]].


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