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Diffstat (limited to 'tcl8.6/doc/unknown.n')
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1 files changed, 91 insertions, 0 deletions
diff --git a/tcl8.6/doc/unknown.n b/tcl8.6/doc/unknown.n new file mode 100644 index 0000000..82dcefc --- /dev/null +++ b/tcl8.6/doc/unknown.n @@ -0,0 +1,91 @@ +'\" +'\" Copyright (c) 1993 The Regents of the University of California. +'\" Copyright (c) 1994-1996 Sun Microsystems, Inc. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +.TH unknown n "" Tcl "Tcl Built-In Commands" +.so man.macros +.BS +'\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +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 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 (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 +through library directories for a command procedure with the name +\fIcmdName\fR, or expanding abbreviated command names to full-length, +or automatically executing unknown commands as sub-processes. +In some cases (such as expanding abbreviations) \fBunknown\fR will +change the original command slightly and then (re-)execute it. +The result of the \fBunknown\fR command is used as the result for +the original non-existent command. +.PP +The default implementation of \fBunknown\fR behaves as follows. +It first calls the \fBauto_load\fR 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 \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 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: +\fB!!\fR, \fB!\fIevent\fR, or \fB^\fIold\fB^\fInew\fR?\fB^\fR?. +If so, then \fBunknown\fR carries out history substitution +in the same way that \fBcsh\fR would for these constructs. +Finally, \fBunknown\fR checks to see if \fIcmd\fR 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, \fBunknown\fR generates an error return. +If the global variable \fBauto_noload\fR is defined, then the auto-load +step is skipped. +If the global variable \fBauto_noexec\fR is defined then the +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, unknown |