unknown(3Tcl)

NAME
     unknown - Handle attempts to use non-existent commands

SYNOPSIS
     unknown cmdName ?arg arg ...?


DESCRIPTION
     This command doesn't actually exist as part of Tcl, but Tcl will invoke
     it if it does exist.  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.


KEYWORDS
     error, non-existent command