parsecmd.3

tcl是工具命令语言

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'\" Copyright (c) 1997 Sun Microsystems, Inc.
'\"
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'\" RCS: @(#) $Id: ParseCmd.3,v 1.10 2002/08/05 03:24:39 dgp Exp $
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.so man.macros
.TH Tcl_ParseCommand 3 8.3 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuotedString, Tcl_ParseVarName, Tcl_ParseVar, Tcl_FreeParse, Tcl_EvalTokens, Tcl_EvalTokensStandard \- parse Tcl scripts and expressions
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_ParseCommand\fR(\fIinterp, string, numBytes, nested, parsePtr\fR)
.sp
int
\fBTcl_ParseExpr\fR(\fIinterp, string, numBytes, parsePtr\fR)
.sp
int
\fBTcl_ParseBraces\fR(\fIinterp, string, numBytes, parsePtr, append, termPtr\fR)
.sp
int
\fBTcl_ParseQuotedString\fR(\fIinterp, string, numBytes, parsePtr, append, termPtr\fR)
.sp
int
\fBTcl_ParseVarName\fR(\fIinterp, string, numBytes, parsePtr, append\fR)
.sp
CONST char *
\fBTcl_ParseVar\fR(\fIinterp, string, termPtr\fR)
.sp
\fBTcl_FreeParse\fR(\fIusedParsePtr\fR)
.sp
Tcl_Obj *
\fBTcl_EvalTokens\fR(\fIinterp, tokenPtr, numTokens\fR)
.sp
Tcl_Obj *
\fBTcl_EvalTokensStandard\fR(\fIinterp, tokenPtr, numTokens\fR)
.SH ARGUMENTS
.AS Tcl_Interp *usedParsePtr
.AP Tcl_Interp *interp out
For procedures other than \fBTcl_FreeParse\fR, \fBTcl_EvalTokens\fR
and \fBTcl_EvalTokensStandard\fR, used only for error reporting;
if NULL, then no error messages are left after errors.
For \fBTcl_EvalTokens\fR and \fBTcl_EvalTokensStandard\fR,
determines the context for evaluating the
script and also is used for error reporting; must not be NULL.
.AP "CONST char" *string in
Pointer to first character in string to parse.
.AP int numBytes in
Number of bytes in \fIstring\fR, not including any terminating null
character.  If less than 0 then the script consists of all characters
in \fIstring\fR up to the first null character.
.AP int nested in
Non-zero means that the script is part of a command substitution so an
unquoted close bracket should be treated as a command terminator.  If zero,
close brackets have no special meaning. 
.AP int append in
Non-zero means that \fI*parsePtr\fR already contains valid tokens; the new
tokens should be appended to those already present.  Zero means that
\fI*parsePtr\fR is uninitialized; any information in it is ignored.
This argument is normally 0.
.AP Tcl_Parse *parsePtr out
Points to structure to fill in with information about the parsed
command, expression, variable name, etc.
Any previous information in this structure
is ignored, unless \fIappend\fR is non-zero in a call to
\fBTcl_ParseBraces\fR, \fBTcl_ParseQuotedString\fR,
or \fBTcl_ParseVarName\fR.
.AP "CONST char" **termPtr out
If not NULL, points to a location where
\fBTcl_ParseBraces\fR, \fBTcl_ParseQuotedString\fR, and
\fBTcl_ParseVar\fR will store a pointer to the character
just after the terminating character (the close-brace, the last
character of the variable name, or the close-quote (respectively))
if the parse was successful.
.AP Tcl_Parse *usedParsePtr in
Points to structure that was filled in by a previous call to
\fBTcl_ParseCommand\fR, \fBTcl_ParseExpr\fR, \fBTcl_ParseVarName\fR, etc.
.BE

.SH DESCRIPTION
.PP
These procedures parse Tcl commands or portions of Tcl commands such as
expressions or references to variables.
Each procedure takes a pointer to a script (or portion thereof)
and fills in the structure pointed to by \fIparsePtr\fR
with a collection of tokens describing the information that was parsed.
The procedures normally return \fBTCL_OK\fR.
However, if an error occurs then they return \fBTCL_ERROR\fR,
leave an error message in \fIinterp's\fR result
(if \fIinterp\fR is not NULL),
and leave nothing in \fIparsePtr\fR.
.PP
\fBTcl_ParseCommand\fR is a procedure that parses Tcl
scripts.  Given a pointer to a script, it
parses the first command from the script.  If the command was parsed
successfully, \fBTcl_ParseCommand\fR returns \fBTCL_OK\fR and fills in the
structure pointed to by \fIparsePtr\fR with information about the
structure of the command (see below for details).
If an error occurred in parsing the command then
\fBTCL_ERROR\fR is returned, an error message is left in \fIinterp\fR's
result, and no information is left at \fI*parsePtr\fR.
.PP
\fBTcl_ParseExpr\fR parses Tcl expressions.
Given a pointer to a script containing an expression,
\fBTcl_ParseCommand\fR parses the expression.
If the expression was parsed successfully,
\fBTcl_ParseExpr\fR returns \fBTCL_OK\fR and fills in the
structure pointed to by \fIparsePtr\fR with information about the
structure of the expression (see below for details).
If an error occurred in parsing the command then
\fBTCL_ERROR\fR is returned, an error message is left in \fIinterp\fR's
result, and no information is left at \fI*parsePtr\fR.
.PP
\fBTcl_ParseBraces\fR parses a string or command argument
enclosed in braces such as
\fB{hello}\fR or \fB{string \\t with \\t tabs}\fR
from the beginning of its argument \fIstring\fR.
The first character of \fIstring\fR must be \fB{\fR. 
If the braced string was parsed successfully,
\fBTcl_ParseBraces\fR returns \fBTCL_OK\fR,
fills in the structure pointed to by \fIparsePtr\fR
with information about the structure of the string
(see below for details),
and stores a pointer to the character just after the terminating \fB}\fR
in the location given by \fI*termPtr\fR.
If an error occurs while parsing the string
then \fBTCL_ERROR\fR is returned,
an error message is left in \fIinterp\fR's result,
and no information is left at \fI*parsePtr\fR or \fI*termPtr\fR.
.PP
\fBTcl_ParseQuotedString\fR parses a double-quoted string such as
\fB"sum is [expr $a+$b]"\fR
from the beginning of the argument \fIstring\fR.
The first character of \fIstring\fR must be \fB"\fR. 
If the double-quoted string was parsed successfully,
\fBTcl_ParseQuotedString\fR returns \fBTCL_OK\fR,
fills in the structure pointed to by \fIparsePtr\fR
with information about the structure of the string
(see below for details),
and stores a pointer to the character just after the terminating \fB"\fR
in the location given by \fI*termPtr\fR.
If an error occurs while parsing the string
then \fBTCL_ERROR\fR is returned,
an error message is left in \fIinterp\fR's result,
and no information is left at \fI*parsePtr\fR or \fI*termPtr\fR.
.PP
\fBTcl_ParseVarName\fR parses a Tcl variable reference such as
\fB$abc\fR or \fB$x([expr $index + 1])\fR from the beginning of its
\fIstring\fR argument.
The first character of \fIstring\fR must be \fB$\fR. 
If a variable name was parsed successfully, \fBTcl_ParseVarName\fR
returns \fBTCL_OK\fR and fills in the structure pointed to by
\fIparsePtr\fR with information about the structure of the variable name
(see below for details).  If an error
occurs while parsing the command then \fBTCL_ERROR\fR is returned, an
error message is left in \fIinterp\fR's result (if \fIinterp\fR isn't
NULL), and no information is left at \fI*parsePtr\fR.
.PP
\fBTcl_ParseVar\fR parse a Tcl variable reference such as \fB$abc\fR
or \fB$x([expr $index + 1])\fR from the beginning of its \fIstring\fR
argument.  The first character of \fIstring\fR must be \fB$\fR.  If
the variable name is parsed successfully, \fBTcl_ParseVar\fR returns a
pointer to the string value of the variable.  If an error occurs while
parsing, then NULL is returned and an error message is left in
\fIinterp\fR's result.
.PP
The information left at \fI*parsePtr\fR
by \fBTcl_ParseCommand\fR, \fBTcl_ParseExpr\fR, \fBTcl_ParseBraces\fR,
\fBTcl_ParseQuotedString\fR, and \fBTcl_ParseVarName\fR
may include dynamically allocated memory.
If these five parsing procedures return \fBTCL_OK\fR
then the caller must invoke \fBTcl_FreeParse\fR to release
the storage at \fI*parsePtr\fR.
These procedures ignore any existing information in
\fI*parsePtr\fR (unless \fIappend\fR is non-zero),
so if repeated calls are being made to any of them
then \fBTcl_FreeParse\fR must be invoked once after each call.
.PP
\fBTcl_EvalTokensStandard\fR evaluates a sequence of parse tokens from
a Tcl_Parse structure.  The tokens typically consist
of all the tokens in a word or all the tokens that make up the index for
a reference to an array variable.  \fBTcl_EvalTokensStandard\fR performs the
substitutions requested by the tokens and concatenates the
resulting values. 
The return value from \fBTcl_EvalTokensStandard\fR is a Tcl completion
code with one of the values \fBTCL_OK\fR, \fBTCL_ERROR\fR,
\fBTCL_RETURN\fR, \fBTCL_BREAK\fR, or \fBTCL_CONTINUE\fR.
In addition, a result value or error message is left in \fIinterp\fR's
result; it can be retrieved using \fBTcl_GetObjResult\fR.
.PP
\fBTcl_EvalTokens\fR differs from \fBTcl_EvalTokensStandard\fR only in
the return convention used: it returns the result in a new Tcl_Obj.
The reference count of the object returned as result has been
incremented, so the caller must
invoke \fBTcl_DecrRefCount\fR when it is finished with the object.
If an error or other exception occurs while evaluating the tokens
(such as a reference to a non-existent variable) then the return value
is NULL and an error message is left in \fIinterp\fR's result. The use
of \fBTcl_EvalTokens\fR is deprecated.

.SH "TCL_PARSE STRUCTURE"
.PP
\fBTcl_ParseCommand\fR, \fBTcl_ParseExpr\fR, \fBTcl_ParseBraces\fR,
\fBTcl_ParseQuotedString\fR, and \fBTcl_ParseVarName\fR
return parse information in two data structures, Tcl_Parse and Tcl_Token:
.CS
typedef struct Tcl_Parse {
	char *\fIcommentStart\fR;
	int \fIcommentSize\fR;
	char *\fIcommandStart\fR;
	int \fIcommandSize\fR;
	int \fInumWords\fR;
	Tcl_Token *\fItokenPtr\fR;
	int \fInumTokens\fR;
	...
} Tcl_Parse;

typedef struct Tcl_Token {
    int \fItype\fR;
    char *\fIstart\fR;