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YACC(1)				 User Commands			       YACC(1)

       Yacc - an LALR(1) parser generator

       yacc [ -dgilrtv ] [ -b file_prefix ] [ -p symbol_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 lan‐
       guage.  Yacc normally writes the parse tables and the driver routine to
       the file

       The following options are available:

       -b file_prefix
	    The	 -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.

       -d   The	 -d  option  causes the header file to be written.  It
	    contains #define's for the token identifiers.

       -g   The -g option causes a  graphical  description  of	the  generated
	    LALR(1) parser to be written to the file in graphviz format,
	    ready to be processed by dot(1).

       -i   The -i option causes a supplementary header	 file	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., is modified to #include this file as well as  the
	    file,  enforcing  consistent usage of the symbols defined in those

	    The supplementary header file makes it simpler to separate	compi‐
	    lation of lex- and yacc-files.

       -l   If	the  -l option is not specified, yacc will insert #line direc‐
	    tives in the generated code.  The #line directives let the C  com‐
	    piler  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

       -o output_file
	    specify the filename for the parser file.  If this option  is  not
	    given,  the	 output	 filename is the file prefix concatenated with
	    the file suffix, e.g.,  This overrides the -p option.

       -p symbol_prefix
	    The -p option changes the prefix prepended to yacc-generated  sym‐
	    bols  to  the string denoted by symbol_prefix.  The default prefix
	    is the string yy.

       -P   create a reentrant parser, e.g., "%pure-parser".

       -r   The -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  The prefix "y." can be  overridden	using  the  -b

       -s   suppress  "#define"	 statements generated for string literals in a
	    "%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 gen‐
	    erates 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".

	    POSIX (IEEE 1003.1 2004) documents	only  names  and  numbers  for
	    "%token", though original yacc and bison also accept string liter‐

       -t   The -t option changes the  preprocessor  directives	 generated  by
	    yacc so that debugging statements will be incorporated in the com‐
	    piled code.

       -v   The -v option causes a human-readable description of the generated
	    parser to be written to the file y.output.

       -V   print the version number to the standard output.

       -y   yacc  ignores  this	 option,  which	 bison supports for ostensible
	    POSIX compatibility.

       yacc provides some extensions for compatibility with  bison  and	 other
       implementations of yacc:

	%expect number
	      tell  yacc  the expected number of shift/reduce conflicts.  That
	      makes it only report the number if it differs.

	%expect-rr number
	      tell yacc the expected number of reduce/reduce conflicts.	  That
	      makes  it only report the number if it differs.  This is (unlike
	      bison) allowable in LALR parsers.

	%lex-param { argument-declaration }
	      By default, the lexer accepts no parameters, e.g., yylex().  Use
	      this directive to add parameter declarations for your customized

	%parse-param { argument-declaration }
	      By default, the parser accepts no parameters,  e.g.,  yyparse().
	      Use  this	 directive to add parameter declarations for your cus‐
	      tomized parser.

	      Most variables (other than yydebug and yynerrs) are allocated on
	      the  stack  within  yyparse,  making the parser reasonably reen‐

       According to Robert Corbett,

	       Berkeley Yacc is an LALR(1) parser generator.  Berkeley Yacc has been made
	   as compatible as possible with AT&T Yacc.  Berkeley Yacc can accept any input
	   specification that conforms to the AT&T Yacc documentation.	Specifications
	   that take advantage of undocumented features of AT&T Yacc will probably be

       The rationale in

       documents some features of AT&T yacc which are no longer	 required  for
       POSIX compliance.

       That  said,  you	 may be interested in reusing grammary files with some
       other implementation which is not strictly compatible with  AT&T	 yacc.
       For instance, there is bison.  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
			 = {

       ·   Yacc and bison emit code in	different  order,  and	in  particular
	   bison  makes	 forward  reference to common functions such as yylex,
	   yyparse and yyerror without providing prototypes.

       ·   Bison's support for "%expect" is broken in more than	 one  release.
	   For best results using bison, delete that directive.

       ·   Bison  has  no equivalent for some of yacc's commmand-line options,
	   relying on directives embedded in the grammar file.

       ·   Bison's "-y" option does not affect bison's	lack  of  support  for
	   features of AT&T yacc which were deemed obsolescent.

       If  there are rules that are never reduced, the number of such rules is
       reported on standard error.  If there are any  LALR(1)  conflicts,  the
       number of conflicts is reported on standard error.

Berkeley Yacc		       September 7, 2011		       YACC(1)

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