tclvars

tclvars, a page in the official documentation, describes the built-in Tcl variables

Documentation edit

$argc: the number of arguments the script was called with.
$argv: a list of arguments passed to the script. Unlike C, $argv does not include the name of the application itself among the argument list. For that, there is $argv0.
$argv0: the name of the interpreter itself
$auto_execs: Used by auto_execok to record information about whether particular commands exist as executable files.
$auto_index: Used by auto_load to save the index information read from disk.
$auto_noexec
$auto_noload
$auto_oldpath
$auto_path
$dir
$env
$env(TCL_LIBRARY)
$env(TCLLIBPATH)
$errorCode
$errorInfo
$tclDefaultLibrary: on unix
$tcl_interactive
$tcl_libpath
$tcl_library: The name of the directory containing the scripts that compose the Tcl system of the current application. Not to be confused with $env(TCL_LIBRARY). The initial value of this variable is determined by finding a directory that contains an appropriate Tcl startup script. Locations from the following sources are searched, in order: $env(TCL_LIBRARY), some other directories based on an internal algorithm, the location of the application executable file, and the current working directory.
$tcl_patchLevel
$tcl_pkgPath
$tcl_platform
$tcl_precision
$tcl_rcFileName
$tcl_rcRsrcName
$tcl_traceCompile
$tcl_traceExec
$tcl_version
$unknown_pending
$tcl_wordchars and $tcl_nonwordchars

There are also a number of special shell environment variables which can influence Tcl behavior. These include: