| YACC(1) | General Commands Manual | YACC(1) | 
yacc —
| yacc | [ -BdgilLPrtvVy] [-bfile_prefix] [-ooutput_file] [-psymbol_prefix] filename | 
yacc reads the grammar specification in the file
  filename and generates an LALR(1) parser for it. The
  parsers consist of a set of LALR(1) parsing tables and a driver routine
  written in the C programming language. yacc normally
  writes the parse tables and the driver routine to the file
  y.tab.c.
The following options are available:
-b
    file_prefix-b option changes the prefix prepended to the
      output file names to the string denoted by
      file_prefix. The default prefix is the character
      ‘y’.-Byacc).-d-d option causes the header file
      y.tab.h to be written. It contains
      #define's for the token identifiers.-g-g option causes a graphical description of
      the generated LALR(1) parser to be written to the file
      y.dot in graphviz format, ready to be processed by
      dot(1).-i-i option causes a supplementary header file
      y.tab.i to be written. It contains extern
      declarations and supplementary #define's as needed
      to map the conventional yacc
      yy-prefixed names to whatever the
      -p option may specify. The code file, e.g.,
      y.tab.c is modified to
      #include this file as well as the
      y.tab.h file, enforcing consistent usage of the
      symbols defined in those files. The supplementary header file makes it
      simpler to separate compilation of lex- and yacc-files.-l-l option is not specified,
      yacc will insert #line
      directives in the generated code. The #line
      directives let the C compiler relate errors in the generated code to the
      user's original code. If the -l option is
      specified, yacc will not insert the
      #line directives. #line
      directives specified by the user will be retained.-L%locations’ (compile-type
      configuration for yacc).-o
    output_file-b option.-P-P options instructs
      yacc to create a reentrant parser, like
      ‘%pure-parser’ does.-p
    symbol_prefix-p option changes the prefix prepended to
      yacc-generated symbols to the string denoted by
      symbol_prefix. The default prefix is the string
      ‘yy’.-r-r option causes yacc
      to produce separate files for code and tables. The code file is named
      y.code.c, and the tables file is named
      y.tab.c. The prefix
      ‘y’ can be overridden using the
      -b option.-s%token’ statement, to
      more closely match original yacc behavior.
    Normally when yacc sees a line such
      as
%token OP_ADD
      "ADD"it notices that the quoted “ADD” is a valid C
        identifier, and generates a #define not only for
        OP_ADD, but for ADD as
        well, e.g.,
#define OP_ADD 257
#define ADD 258
    
    The original yacc does not generate
        the second #define. The
        -s option suppresses this
        #define.
IEEE Std 1003.1
        (“POSIX.1”) documents only names and numbers for
        ‘%token’, though the original
        yacc and
        bison(1) also accept string
        literals.
-t-t option changes the preprocessor directives
      generated by yacc so that debugging statements
      will be incorporated in the compiled code.-V-V option prints the version number to the
      standard output.-v-v option causes a human-readable description
      of the generated parser to be written to the file
      y.output.-yyacc ignores this option, which
      bison(1) supports for
      ostensible POSIX compatibility.yacc provides some extensions for compatibility with
  bison(1) and other
  implementations of yacc. The
  ‘%destructor’ and
  ‘%locations’ features are available only
  if yacc has been configured and compiled to support
  the back-tracking functionality. The remaining features are always available:
%destructor
    { code }
    symbol+On encountering a parse error, the generated parser discards symbols on the stack and input tokens until it reaches a state that will allow parsing to continue. This error recovery approach results in a memory leak if the YYSTYPE value is, or contains, pointers to dynamically allocated memory.
The bracketed code is invoked whenever
        the parser discards one of the symbols. Within it
        ‘$$’ or
        ‘$<tag>$’
        designates the semantic value associated with the discarded symbol, and
        ‘@$’ designates its location (see
        ‘%locations’ directive).
A per-symbol destructor is defined by listing a grammar symbol
        in symbol+. A per-type destructor is defined by
        listing a semantic type tag (e.g.,
        ‘<some_tag>’)
        in symbol+; in this case, the parser will invoke
        code whenever it discards any grammar symbol that
        has that semantic type tag, unless that symbol has its own per-symbol
        destructor.
Two categories of default destructor are supported that are invoked when discarding any grammar symbol that has no per-symbol and no per-type destructor:
The code for ‘<*>’
        is used for grammar symbols that have an explicitly declared semantic
        type tag (via ‘%type’);
The code for ‘<>’
        is used for grammar symbols that have no declared semantic type tag.
%expect
    numberyacc the expected number of shift/reduce
      conflicts. That makes it only report the number if it differs.%expect-rr
    numberyacc the expected number of reduce/reduce
      conflicts. That makes it only report the number if it differs. This is,
      unlike bison(1), allowable in
      LALR(1) parsers.%locationsyacc to enable management of position
      information associated with each token, provided by the lexer in the
      global variable yylloc, similar to management of
      semantic value information provided in yylval.
    As for semantic values, locations can be referenced within
        actions using ‘@$’ to refer to the
        location of the left hand side symbol, and
        ‘@N’
        (N an integer) to refer to the location of one of
        the right hand side symbols. Also as for semantic values, when a rule is
        matched, a default action is used the compute the location represented
        by ‘@$’ as the beginning of the
        first symbol and the end of the last symbol in the right hand side of
        the rule. This default computation can be overridden by explicit
        assignment to ‘@$’ in a rule
        action.
The type of yylloc is YYLTYPE, which is defined by default as:
typedef struct YYLTYPE {
    int first_line;
    int first_column;
    int last_line;
    int last_column;
} YYLTYPE;
    
    YYLTYPE can be redefined by the user
        (YYLTYPE_IS_DEFINED must be defined, to inhibit
        the default) in the declarations section of the specification file. As
        in bison(1), the macro
        YYLLOC_DEFAULT is invoked each time a rule is
        matched to calculate a position for the left hand side of the rule,
        before the associated action is executed; this macro can be redefined by
        the user.
This directive adds a YYLTYPE parameter
        to yyerror(). If the
        ‘%pure-parser’ directive is
        present, a YYLTYPE parameter is added to
        yylex() calls.
%lex-param
    { argument-declaration
    }yylex(). Use this directive to add parameter
      declarations for your customized lexer.%parse-param
    { argument-declaration
    }yyparse(). Use this directive to add parameter
      declarations for your customized parser.%pure-parseryyparse(), making the parser reasonably
    reentrant.%token-tableyacc
      yacc does not predefine “$end”, “$error” or
      “$undefined” in this array.The rationale in http://pubs.opengroup.org/onlinepubs/9699919799/utilities/yacc.html documents some features of AT&T yacc which are no longer required for POSIX compliance.
That said, you may be interested in reusing grammar files with some other implementation which is not strictly compatible with AT&T yacc. For instance, there is bison(1). Here are a few differences:
yacc accepts an equals mark preceding the
    left curly brace of an action (as in the original grammar file
    ftp.y):
    |	STAT CRLF
	= {
		statcmd();
	}
yacc and
    bison(1) emit code in different
    order, and in particular
    bison(1) makes forward
    reference to common functions such as yylex(),
    yyparse() and yyerror()
    without providing prototypes.
bison(1) support for
    ‘%expect’ is broken in more than one
    release. For best results using
    bison(1), delete that
    directive.
bison(1) has no
    equivalent for some of yacc's command-line options,
    relying on directives embedded in the grammar file.
bison(1)
    -y option does not affect bison's lack of support
    for features of AT&T yacc which were deemed obsolescent.
yacc accepts multiple parameters with
    ‘%lex-param’ and
    ‘%parse-param’ in two forms
{type1 name1} {type2 name2} ...
{type1 name1,  type2 name2 ...}
bison(1) accepts the latter (though undocumented), but depending on the release may generate bad code.
Like bison(1),
    yacc will add parameters specified via
    ‘%parse-param’ to
    yyparse(), yyerror() and (if
    configured for back-tracking) to the destructor declared using
    ‘%destructor’.
bison(1) puts the
    additional parameters first for
    yyparse() and yyerror() but
    last for destructors. yacc matches
    this behavior.
yacc:
TMPDIRTMPDIR is set, the
      string denoted by TMPDIR will be used as the name
      of the directory where the temporary files are created.yacc are yylhs,
  yylen, yydefred,
  yydgoto, yysindex,
  yyrindex, yygindex,
  yytable, and yycheck. Two
  additional tables, yyname and
  yyrule, are created if YYDEBUG
  is defined and non-zero.
yacc utility conforms to IEEE Std
  1003.2 (“POSIX.2”).
| October 5, 2014 | NetBSD 10.0 |