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RedHat 9 (Linux i386) - man page for unknown (redhat section n)

unknown(n)			      Tcl Built-In Commands			       unknown(n)

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NAME
       unknown - Handle attempts to use non-existent commands

SYNOPSIS
       unknown cmdName ?arg arg ...?
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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 com-
       mand, 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_exe-
       cok 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  substi-
       tution  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  circum-
       stances	the return value from unknown is the return value from the command that was even-
       tually executed.

SEE ALSO
       info(n), proc(n)

KEYWORDS
       error, non-existent command

Tcl										       unknown(n)


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