Tcl_ParseCommand(3) Tcl Library Procedures Tcl_ParseCommand(3) ______________________________________________________________________________
NAME
Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces,
Tcl_ParseQuotedString, Tcl_ParseVarName, Tcl_ParseVar, Tcl_FreeParse,
Tcl_EvalTokens, Tcl_EvalTokensStandard - parse Tcl scripts and
expressions
SYNOPSIS
#include <tcl.h>
int
Tcl_ParseCommand(interp, start, numBytes, nested, parsePtr)
int
Tcl_ParseExpr(interp, start, numBytes, parsePtr)
int
Tcl_ParseBraces(interp, start, numBytes, parsePtr, append, termPtr)
int
Tcl_ParseQuotedString(interp, start, numBytes, parsePtr, append, termPtr)
int
Tcl_ParseVarName(interp, start, numBytes, parsePtr, append)
const char *
Tcl_ParseVar(interp, start, termPtr)
Tcl_FreeParse(usedParsePtr)
Tcl_Obj *
Tcl_EvalTokens(interp, tokenPtr, numTokens)
int
Tcl_EvalTokensStandard(interp, tokenPtr, numTokens)
ARGUMENTS
Tcl_Interp *interp (out) For procedures other than
Tcl_FreeParse, Tcl_EvalTokens
and Tcl_EvalTokensStandard, used
only for error reporting; if
NULL, then no error messages are
left after errors. For
Tcl_EvalTokens and
Tcl_EvalTokensStandard,
determines the context for
evaluating the script and also
is used for error reporting;
must not be NULL.
const char *start (in) Pointer to first character in
string to parse.
int numBytes (in) Number of bytes in string to
parse, not including any
terminating null character. If
less than 0 then the script
consists of all characters
following start up to the first
null character.
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.
int append (in) Non-zero means that *parsePtr
already contains valid tokens;
the new tokens should be
appended to those already
present. Zero means that
*parsePtr is uninitialized; any
information in it is ignored.
This argument is normally 0.
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
append is non-zero in a call to
Tcl_ParseBraces,
Tcl_ParseQuotedString, or
Tcl_ParseVarName.
const char **termPtr (out) If not NULL, points to a
location where Tcl_ParseBraces,
Tcl_ParseQuotedString, and
Tcl_ParseVar 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.
Tcl_Parse *usedParsePtr (in) Points to structure that was
filled in by a previous call to
Tcl_ParseCommand, Tcl_ParseExpr,
Tcl_ParseVarName, etc.
______________________________________________________________________________
DESCRIPTION
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 parsePtr with a collection of tokens describing the information that
was parsed. The procedures normally return TCL_OK. However, if an
error occurs then they return TCL_ERROR, leave an error message in
interp's result (if interp is not NULL), and leave nothing in parsePtr.
Tcl_ParseCommand 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, Tcl_ParseCommand returns TCL_OK
and fills in the structure pointed to by parsePtr with information
about the structure of the command (see below for details). If an
error occurred in parsing the command then TCL_ERROR is returned, an
error message is left in interp's result, and no information is left at
*parsePtr.
Tcl_ParseExpr parses Tcl expressions. Given a pointer to a script
containing an expression, Tcl_ParseExpr parses the expression. If the
expression was parsed successfully, Tcl_ParseExpr returns TCL_OK and
fills in the structure pointed to by parsePtr with information about
the structure of the expression (see below for details). If an error
occurred in parsing the command then TCL_ERROR is returned, an error
message is left in interp's result, and no information is left at
*parsePtr.
Tcl_ParseBraces parses a string or command argument enclosed in braces
such as {hello} or {string \t with \t tabs} from the beginning of its
argument start. The first character of start must be {. If the braced
string was parsed successfully, Tcl_ParseBraces returns TCL_OK, fills
in the structure pointed to by parsePtr with information about the
structure of the string (see below for details), and stores a pointer
to the character just after the terminating } in the location given by
*termPtr. If an error occurs while parsing the string then TCL_ERROR
is returned, an error message is left in interp's result, and no
information is left at *parsePtr or *termPtr.
Tcl_ParseQuotedString parses a double-quoted string such as "sum is
[expr {$a+$b}]" from the beginning of the argument start. The first
character of start must be ". If the double-quoted string was parsed
successfully, Tcl_ParseQuotedString returns TCL_OK, fills in the
structure pointed to by parsePtr with information about the structure
of the string (see below for details), and stores a pointer to the
character just after the terminating " in the location given by
*termPtr. If an error occurs while parsing the string then TCL_ERROR
is returned, an error message is left in interp's result, and no
information is left at *parsePtr or *termPtr.
Tcl_ParseVarName parses a Tcl variable reference such as $abc or
$x([expr {$index + 1}]) from the beginning of its start argument. The
first character of start must be $. If a variable name was parsed
successfully, Tcl_ParseVarName returns TCL_OK and fills in the
structure pointed to by parsePtr with information about the structure
of the variable name (see below for details). If an error occurs while
parsing the command then TCL_ERROR is returned, an error message is
left in interp's result (if interp is not NULL), and no information is
left at *parsePtr.
Tcl_ParseVar parses a Tcl variable reference such as $abc or $x([expr
{$index + 1}]) from the beginning of its start argument. The first
character of start must be $. If the variable name is parsed
successfully, Tcl_ParseVar 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 interp's result.
The information left at *parsePtr by Tcl_ParseCommand, Tcl_ParseExpr,
Tcl_ParseBraces, Tcl_ParseQuotedString, and Tcl_ParseVarName may
include dynamically allocated memory. If these five parsing procedures
return TCL_OK then the caller must invoke Tcl_FreeParse to release the
storage at *parsePtr. These procedures ignore any existing information
in *parsePtr (unless append is non-zero), so if repeated calls are
being made to any of them then Tcl_FreeParse must be invoked once after
each call.
Tcl_EvalTokensStandard 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. Tcl_EvalTokensStandard performs the substitutions
requested by the tokens and concatenates the resulting values. The
return value from Tcl_EvalTokensStandard is a Tcl completion code with
one of the values TCL_OK, TCL_ERROR, TCL_RETURN, TCL_BREAK, or
TCL_CONTINUE, or possibly some other integer value originating in an
extension. In addition, a result value or error message is left in
interp's result; it can be retrieved using Tcl_GetObjResult.
Tcl_EvalTokens differs from Tcl_EvalTokensStandard only in the return
convention used: it returns the result in a new Tcl_Obj. The reference
count of the value returned as result has been incremented, so the
caller must invoke Tcl_DecrRefCount when it is finished with the value.
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 interp's result. The use of
Tcl_EvalTokens is deprecated.
TCL_PARSE STRUCTURE
Tcl_ParseCommand, Tcl_ParseExpr, Tcl_ParseBraces,
Tcl_ParseQuotedString, and Tcl_ParseVarName return parse information in
two data structures, Tcl_Parse and Tcl_Token:
typedef struct Tcl_Parse {
const char *commentStart;
int commentSize;
const char *commandStart;
int commandSize;
int numWords;
Tcl_Token *tokenPtr;
int numTokens;
...
} Tcl_Parse;
typedef struct Tcl_Token {
int type;
const char *start;
int size;
int numComponents;
} Tcl_Token;
The first five fields of a Tcl_Parse structure are filled in only by
Tcl_ParseCommand. These fields are not used by the other parsing
procedures.
Tcl_ParseCommand fills in a Tcl_Parse structure with information that
describes one Tcl command and any comments that precede the command.
If there are comments, the commentStart field points to the # character
that begins the first comment and commentSize indicates the number of
bytes in all of the comments preceding the command, including the
newline character that terminates the last comment. If the command is
not preceded by any comments, commentSize is 0. Tcl_ParseCommand also
sets the commandStart field to point to the first character of the
first word in the command (skipping any comments and leading space) and
commandSize gives the total number of bytes in the command, including
the character pointed to by commandStart up to and including the
newline, close bracket, or semicolon character that terminates the
command. The numWords field gives the total number of words in the
command.
All parsing procedures set the remaining fields, tokenPtr and
numTokens. The tokenPtr field points to the first in an array of
Tcl_Token structures that describe the components of the entity being
parsed. The numTokens field gives the total number of tokens present
in the array. Each token contains four fields. The type field selects
one of several token types that are described below. The start field
points to the first character in the token and the size field gives the
total number of characters in the token. Some token types, such as
TCL_TOKEN_WORD and TCL_TOKEN_VARIABLE, consist of several component
tokens, which immediately follow the parent token; the numComponents
field describes how many of these there are. The type field has one of
the following values:
TCL_TOKEN_WORD This token ordinarily describes one word of a
command but it may also describe a quoted or braced
string in an expression. The token describes a
component of the script that is the result of
concatenating together a sequence of subcomponents,
each described by a separate subtoken. The token
starts with the first non-blank character of the
component (which may be a double-quote or open
brace) and includes all characters in the component
up to but not including the space, semicolon, close
bracket, close quote, or close brace that
terminates the component. The numComponents field
counts the total number of sub-tokens that make up
the word, including sub-tokens of
TCL_TOKEN_VARIABLE and TCL_TOKEN_BS tokens.
TCL_TOKEN_SIMPLE_WORD
This token has the same meaning as TCL_TOKEN_WORD,
except that the word is guaranteed to consist of a
single TCL_TOKEN_TEXT sub-token. The numComponents
field is always 1.
TCL_TOKEN_EXPAND_WORD
This token has the same meaning as TCL_TOKEN_WORD,
except that the command parser notes this word
began with the expansion prefix {*}, indicating
that after substitution, the list value of this
word should be expanded to form multiple arguments
in command evaluation. This token type can only be
created by Tcl_ParseCommand.
TCL_TOKEN_TEXT The token describes a range of literal text that is
part of a word. The numComponents field is always
0.
TCL_TOKEN_BS The token describes a backslash sequence such as \n
or \0xA3. The numComponents field is always 0.
TCL_TOKEN_COMMAND The token describes a command whose result must be
substituted into the word. The token includes the
square brackets that surround the command. The
numComponents field is always 0 (the nested command
is not parsed; call Tcl_ParseCommand recursively if
you want to see its tokens).
TCL_TOKEN_VARIABLE The token describes a variable substitution,
including the $, variable name, and array index (if
there is one) up through the close parenthesis that
terminates the index. This token is followed by
one or more additional tokens that describe the
variable name and array index. If numComponents
is 1 then the variable is a scalar and the next
token is a TCL_TOKEN_TEXT token that gives the
variable name. If numComponents is greater than 1
then the variable is an array: the first sub-token
is a TCL_TOKEN_TEXT token giving the array name and
the remaining sub-tokens are TCL_TOKEN_TEXT,
TCL_TOKEN_BS, TCL_TOKEN_COMMAND, and
TCL_TOKEN_VARIABLE tokens that must be concatenated
to produce the array index. The numComponents field
includes nested sub-tokens that are part of
TCL_TOKEN_VARIABLE tokens in the array index.
TCL_TOKEN_SUB_EXPR The token describes one subexpression of an
expression (or an entire expression). A
subexpression may consist of a value such as an
integer literal, variable substitution, or
parenthesized subexpression; it may also consist of
an operator and its operands. The token starts
with the first non-blank character of the
subexpression up to but not including the space,
brace, close-paren, or bracket that terminates the
subexpression. This token is followed by one or
more additional tokens that describe the
subexpression. If the first sub-token after the
TCL_TOKEN_SUB_EXPR token is a TCL_TOKEN_OPERATOR
token, the subexpression consists of an operator
and its token operands. If the operator has no
operands, the subexpression consists of just the
TCL_TOKEN_OPERATOR token. Each operand is
described by a TCL_TOKEN_SUB_EXPR token.
Otherwise, the subexpression is a value described
by one of the token types TCL_TOKEN_WORD,
TCL_TOKEN_TEXT, TCL_TOKEN_BS, TCL_TOKEN_COMMAND,
TCL_TOKEN_VARIABLE, and TCL_TOKEN_SUB_EXPR. The
numComponents field counts the total number of sub-
tokens that make up the subexpression; this
includes the sub-tokens for any nested
TCL_TOKEN_SUB_EXPR tokens.
TCL_TOKEN_OPERATOR The token describes one operator of an expression
such as && or hypot. A TCL_TOKEN_OPERATOR token is
always preceded by a TCL_TOKEN_SUB_EXPR token that
describes the operator and its operands; the
TCL_TOKEN_SUB_EXPR token's numComponents field can
be used to determine the number of operands. A
binary operator such as * is followed by two
TCL_TOKEN_SUB_EXPR tokens that describe its
operands. A unary operator like - is followed by a
single TCL_TOKEN_SUB_EXPR token for its operand.
If the operator is a math function such as log10,
the TCL_TOKEN_OPERATOR token will give its name and
the following TCL_TOKEN_SUB_EXPR tokens will
describe its operands; if there are no operands (as
with rand), no TCL_TOKEN_SUB_EXPR tokens follow.
There is one trinary operator, ?, that appears in
if-then-else subexpressions such as x?y:z; in this
case, the ? TCL_TOKEN_OPERATOR token is followed by
three TCL_TOKEN_SUB_EXPR tokens for the operands x,
y, and z. The numComponents field for a
TCL_TOKEN_OPERATOR token is always 0.
After Tcl_ParseCommand returns, the first token pointed to by the
tokenPtr field of the Tcl_Parse structure always has type
TCL_TOKEN_WORD or TCL_TOKEN_SIMPLE_WORD or TCL_TOKEN_EXPAND_WORD. It
is followed by the sub-tokens that must be concatenated to produce the
value of that word. The next token is the TCL_TOKEN_WORD or
TCL_TOKEN_SIMPLE_WORD of TCL_TOKEN_EXPAND_WORD token for the second
word, followed by sub-tokens for that word, and so on until all
numWords have been accounted for.
After Tcl_ParseExpr returns, the first token pointed to by the tokenPtr
field of the Tcl_Parse structure always has type TCL_TOKEN_SUB_EXPR.
It is followed by the sub-tokens that must be evaluated to produce the
value of the expression. Only the token information in the Tcl_Parse
structure is modified: the commentStart, commentSize, commandStart, and
commandSize fields are not modified by Tcl_ParseExpr.
After Tcl_ParseBraces returns, the array of tokens pointed to by the
tokenPtr field of the Tcl_Parse structure will contain a single
TCL_TOKEN_TEXT token if the braced string does not contain any
backslash-newlines. If the string does contain backslash-newlines, the
array of tokens will contain one or more TCL_TOKEN_TEXT or TCL_TOKEN_BS
sub-tokens that must be concatenated to produce the value of the
string. If the braced string was just {} (that is, the string was
empty), the single TCL_TOKEN_TEXT token will have a size field
containing zero; this ensures that at least one token appears to
describe the braced string. Only the token information in the
Tcl_Parse structure is modified: the commentStart, commentSize,
commandStart, and commandSize fields are not modified by
Tcl_ParseBraces.
After Tcl_ParseQuotedString returns, the array of tokens pointed to by
the tokenPtr field of the Tcl_Parse structure depends on the contents
of the quoted string. It will consist of one or more TCL_TOKEN_TEXT,
TCL_TOKEN_BS, TCL_TOKEN_COMMAND, and TCL_TOKEN_VARIABLE sub-tokens.
The array always contains at least one token; for example, if the
argument start is empty, the array returned consists of a single
TCL_TOKEN_TEXT token with a zero size field. Only the token
information in the Tcl_Parse structure is modified: the commentStart,
commentSize, commandStart, and commandSize fields are not modified.
After Tcl_ParseVarName returns, the first token pointed to by the
tokenPtr field of the Tcl_Parse structure always has type
TCL_TOKEN_VARIABLE. It is followed by the sub-tokens that make up the
variable name as described above. The total length of the variable
name is contained in the size field of the first token. As in
Tcl_ParseExpr, only the token information in the Tcl_Parse structure is
modified by Tcl_ParseVarName: the commentStart, commentSize,
commandStart, and commandSize fields are not modified.
All of the character pointers in the Tcl_Parse and Tcl_Token structures
refer to characters in the start argument passed to Tcl_ParseCommand,
Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuotedString, and
Tcl_ParseVarName.
There are additional fields in the Tcl_Parse structure after the
numTokens field, but these are for the private use of Tcl_ParseCommand,
Tcl_ParseExpr, Tcl_ParseBraces, Tcl_ParseQuotedString, and
Tcl_ParseVarName; they should not be referenced by code outside of
these procedures.
KEYWORDS
backslash substitution, braces, command, expression, parse, token,
variable substitution
Tcl 8.3 Tcl_ParseCommand(3)
tcl 8.6.14 - Generated Sun Mar 3 06:27:45 CST 2024