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diff --git a/doc/unknown.n b/doc/unknown.n new file mode 100644 index 0000000..a7be942 --- /dev/null +++ b/doc/unknown.n @@ -0,0 +1,75 @@ +'\" +'\" 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. +'\" +'\" SCCS: @(#) unknown.n 1.8 96/10/09 08:29:28 +'\" +.so man.macros +.TH unknown n "" Tcl "Tcl Built-In Commands" +.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 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. +.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 +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 can't 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 KEYWORDS +error, non-existent command |