unknown(1tcl)

unknown -- handle attempts to use non-existent commands

Synopsis

unknown cmdName [arg arg ...]

Description

This command is not a core part of Tcl, but Tcl will invoke it if it does exist (that is, if a function called unknown has been written and linked to Tcl in the current application). 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.