unknown (n)

SYNOPSIS

unknown cmdName ?arg arg ...?

DESCRIPTION

This command is invoked by the Tcl interpreter whenever a script tries to invoke a command that doesn't exist. The implementation of unknown isn't part of the Tcl core; instead, it is a library procedure defined by default when Tcl starts up. You can override the default unknown to change its functionality.

If the Tcl interpreter encounters a command name for which there is not a defined command, then Tcl checks for the existence of a command named unknown. If there is no such command, then the interpreter returns an error. If the unknown command exists, then it is invoked with arguments consisting of the fully-substituted name and arguments for the original non-existent command. The unknown command typically does things like searching through library directories for a command procedure with the name cmdName, or expanding abbreviated command names to full-length, or automatically executing unknown commands as sub-processes. In some cases (such as expanding abbreviations) unknown will change the original command slightly and then (re-)execute it. The result of the unknown command is used as the result for the original non-existent command.

The default implementation of unknown behaves as follows. It first calls the auto_load library procedure to load the command. If this succeeds, then it executes the original command with its original arguments. If the auto-load fails then unknown calls auto_execok to see if there is an executable file by the name cmd. If so, it invokes the Tcl exec command with cmd and all the args as arguments. If cmd can't be auto-executed, unknown checks to see if the command was invoked at top-level and outside of any script. If so, then unknown takes two additional steps. First, it sees if cmd has one of the following three forms: !!, !event, or ^old^new?^?. If so, then unknown carries out history substitution in the same way that csh would for these constructs. Finally, unknown checks to see if cmd is a unique abbreviation for an existing Tcl command. If so, it expands the command name and executes the command with the original arguments. If none of the above efforts has been able to execute the command, unknown generates an error return. If the global variable auto_noload is defined, then the auto-load step is skipped. If the global variable auto_noexec is defined then the auto-exec step is skipped. Under normal circumstances the return value from unknown is the return value from the command that was eventually executed.

KEYWORDS

error, non-existent command '\" '\" Copyright (c) 1993 The Regents of the University of California. '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" '\" RCS: @(#) $Id: unset.n,v 1.2 1998/09/14 18:39:56 stanton Exp $ '\" '\" The definitions below are for supplemental macros used in Tcl/Tk '\" manual entries. '\" '\" .AP type name in/out ?indent? '\" Start paragraph describing an argument to a library procedure. '\" type is type of argument (int, etc.), in/out is either "in", "out", '\" or "in/out" to describe whether procedure reads or modifies arg, '\" and indent is equivalent to second arg of .IP (shouldn't ever be '\" needed; use .AS below instead) '\" '\" .AS ?type? ?name? '\" Give maximum sizes of arguments for setting tab stops. Type and '\" name are examples of largest possible arguments that will be passed '\" to .AP later. If args are omitted, default tab stops are used. '\" '\" .BS '\" Start box enclosure. From here until next .BE, everything will be '\" enclosed in one large box. '\" '\" .BE '\" End of box enclosure. '\" '\" .CS '\" Begin code excerpt. '\" '\" .CE '\" End code excerpt. '\" '\" .VS ?version? ?br? '\" Begin vertical sidebar, for use in marking newly-changed parts '\" of man pages. The first argument is ignored and used for recording '\" the version when the .VS was added, so that the sidebars can be '\" found and removed when they reach a certain age. If another argument '\" is present, then a line break is forced before starting the sidebar. '\" '\" .VE '\" End of vertical sidebar. '\" '\" .DS '\" Begin an indented unfilled display. '\" '\" .DE '\" End of indented unfilled display. '\" '\" .SO '\" Start of list of standard options for a Tk widget. The '\" options follow on successive lines, in four columns separated '\" by tabs. '\" '\" .SE '\" End of list of standard options for a Tk widget. '\" '\" .OP cmdName dbName dbClass '\" Start of description of a specific option. cmdName gives the '\" option's name as specified in the class command, dbName gives '\" the option's name in the option database, and dbClass gives '\" the option's class in the option database. '\" '\" .UL arg1 arg2 '\" Print arg1 underlined, then print arg2 normally. '\" '\" RCS: @(#) $Id: man.macros,v 1.2 1998/09/14 18:39:54 stanton Exp $ '\" '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. t .wh -1.3i ^B ^l \n(.l b '\" # Start an argument description AP !"\\$4"" .TP \\$4 \{\ !"\\$2"" .TP \\n()Cu .TP 15