diff options
Diffstat (limited to 'doc/unknown.n')
| -rw-r--r-- | doc/unknown.n | 46 |
1 files changed, 31 insertions, 15 deletions
diff --git a/doc/unknown.n b/doc/unknown.n index 19f5ac1..cdfbe43 100644 --- a/doc/unknown.n +++ b/doc/unknown.n @@ -5,10 +5,8 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: unknown.n,v 1.2 1998/09/14 18:39:56 stanton Exp $ -'\" -.so man.macros .TH unknown n "" Tcl "Tcl Built-In Commands" +.so man.macros .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME @@ -16,21 +14,24 @@ unknown \- Handle attempts to use non-existent commands .SH SYNOPSIS \fBunknown \fIcmdName \fR?\fIarg arg ...\fR? .BE - .SH DESCRIPTION .PP This command is invoked by the Tcl interpreter whenever a script -tries to invoke a command that doesn't exist. The implementation -of \fBunknown\fR 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 \fBunknown\fR to change its functionality. +tries to invoke a command that does not exist. The default implementation +of \fBunknown\fR is a library procedure defined when Tcl initializes an +interpreter. You can override the default \fBunknown\fR to change its +functionality, or you can register a new handler for individual namespaces +using the \fBnamespace unknown\fR command. Note that there is no default +implementation of \fBunknown\fR in a safe interpreter. .PP 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 \fBunknown\fR. -If there is no such command, then the interpreter returns an -error. -If the \fBunknown\fR command exists, then it is invoked with +is not a defined command (in either the current namespace, or the +global namespace), then Tcl checks for the existence of +an unknown handler for the current namespace. By default, this +handler is a command named \fB::unknown\fR. If there is no such +command, then the interpreter returns an error. +If the \fBunknown\fR command exists (or a new handler has been +registered for the current namespace), then it is invoked with arguments consisting of the fully-substituted name and arguments for the original non-existent command. The \fBunknown\fR command typically does things like searching @@ -50,7 +51,7 @@ If the auto-load fails then \fBunknown\fR calls \fBauto_execok\fR to see if there is an executable file by the name \fIcmd\fR. If so, it invokes the Tcl \fBexec\fR command with \fIcmd\fR and all the \fIargs\fR as arguments. -If \fIcmd\fR can't be auto-executed, \fBunknown\fR checks to +If \fIcmd\fR cannot be auto-executed, \fBunknown\fR checks to see if the command was invoked at top-level and outside of any script. If so, then \fBunknown\fR takes two additional steps. First, it sees if \fIcmd\fR has one of the following three forms: @@ -70,6 +71,21 @@ auto-exec step is skipped. Under normal circumstances the return value from \fBunknown\fR is the return value from the command that was eventually executed. +.SH EXAMPLE +Arrange for the \fBunknown\fR command to have its standard behavior +except for first logging the fact that a command was not found: +.PP +.CS +# Save the original one so we can chain to it +rename \fBunknown\fR _original_unknown +# Provide our own implementation +proc \fBunknown\fR args { + puts stderr "WARNING: unknown command: $args" + uplevel 1 [list _original_unknown {*}$args] +} +.CE +.SH "SEE ALSO" +info(n), proc(n), interp(n), library(n), namespace(n) .SH KEYWORDS -error, non-existent command +error, non-existent command, unknown |