unknown(n) - phpMan

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



_________________________________________________________________________________________________

NAME
       unknown - Handle attempts to use non-existent commands

SYNOPSIS
       unknown cmdName ?arg arg ...?
_________________________________________________________________

DESCRIPTION
       This command is invoked by the Tcl interpreter whenever a script tries to invoke a command
       that does not exist.  The default implementation of unknown is a library procedure defined
       when  Tcl  initializes an interpreter.  You can override the default unknown to change its
       functionality, or you can register a new  handler  for  individual  namespaces  using  the
       namespace  unknown  command.  Note that there is no default implementation of unknown in a
       safe interpreter.

       If the Tcl interpreter encounters a command name for which there is not a defined  command
       (in  either the current namespace, or the global namespace), then Tcl checks for the exis-
       tence of an unknown handler for the current namespace. By default, this handler is a  com-
       mand named ::unknown.  If there is no such command, then the interpreter returns an error.
       If the unknown command exists (or a new handler has been registered for the current names-
       pace),  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 cannot 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.

EXAMPLE
       Arrange for the unknown command to have its standard behavior except for first logging the
       fact that a command was not found:

              # Save the original one so we can chain to it
              rename unknown _original_unknown

              # Provide our own implementation
              proc unknown args {
                  puts stderr "WARNING: unknown command: $args"
                  uplevel 1 [list _original_unknown {*}$args]
              }

SEE ALSO
       info(n), proc(n), interp(n), library(n), namespace(n)

KEYWORDS
       error, non-existent command



Tcl                                                                                    unknown(n)

Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2024-04-19 22:21 @18.218.129.100 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)