YACC(1) User Commands YACC(1)


yacc - yet another compiler-compiler


yacc [-dltVv] [-b file_prefix] [-Q [y | n]]
[-P parser] [-p sym_prefix] file


The yacc command converts a context-free grammar into a set of tables for
a simple automaton that executes an LALR(1) parsing algorithm. The
grammar can be ambiguous. Specified precedence rules are used to break

The output file, y.tab.c, must be compiled by the C compiler to produce a
function yyparse(). This program must be loaded with the lexical analyzer
program, yylex(), as well as main() and yyerror(), an error handling
routine. These routines must be supplied by the user. The lex(1) command
is useful for creating lexical analyzers usable by yacc.


The following options are supported:

-b file_prefix
Uses file_prefix instead of y as the prefix for all
output files. The code file y.tab.c, the header file
y.tab.h (created when -d is specified), and the
description file y.output (created when -v is
specified), is changed to file_prefix.tab.c,
file_prefix.tab.h, and file_prefix.output,

Generates the file y.tab.h with the #define statements
that associate the yacc user-assigned "token codes"
with the user-declared "token names". This association
allows source files other than y.tab.c to access the
token codes.

Specifies that the code produced in y.tab.c does not
contain any #line constructs. This option should only
be used after the grammar and the associated actions
are fully debugged.

-p sym_prefix
Uses sym_prefix instead of yy as the prefix for all
external names produced by yacc. The names affected
include the functions yyparse(), yylex() and yyerror(),
and the variables yylval, yychar and yydebug. (In the
remainder of this section, the six symbols cited are
referenced using their default names only as a
notational convenience.) Local names can also be
affected by the -p option. However, the -p option does
not affect #define symbols generated by yacc.

-P parser
Allows you to specify the parser of your choice instead
of /usr/share/lib/ccs/yaccpar. For example, you can

example% yacc -P ~/myparser parser.y

The -Qy option puts the version stamping information in
y.tab.c. This allows you to know what version of yacc
built the file. The -Qn option (the default) writes no
version information.

Compiles runtime debugging code by default. Runtime
debugging code is always generated in y.tab.c under
conditional compilation control. By default, this code
is not included when y.tab.c is compiled. Whether or
not the -t option is used, the runtime debugging code
is under the control of YYDEBUG , a preprocessor
symbol. If YYDEBUG has a non-zero value, then the
debugging code is included. If its value is 0, then the
code is not included. The size and execution time of a
program produced without the runtime debugging code is
smaller and slightly faster.

Prepares the file y.output, which contains a
description of the parsing tables and a report on
conflicts generated by ambiguities in the grammar.

Prints on the standard error output the version
information for yacc.


The following operand is required:

A path name of a file containing instructions for which a parser
is to be created.


Example 1: Accessing the yacc Library

Access to the yacc library is obtained with library search operands to
cc. To use the yacc library main:

example% cc y.tab.c -ly

Both the lex library and the yacc library contain main. To access the
yacc main:

example% cc y.tab.c lex.yy.c -ly -ll

This ensures that the yacc library is searched first, so that its main is

The historical yacc libraries have contained two simple functions that
are normally coded by the application programmer. These library functions
are similar to the following code:

#include <locale.h>
int main(void)
extern int yyparse();

setlocale(LC_ALL, "");

/* If the following parser is one created by lex, the
application must be careful to ensure that LC_CTYPE
and LC_COLLATE are set to the POSIX locale. */
(void) yyparse();
return (0);

#include <stdio.h>

int yyerror(const char *msg)
(void) fprintf(stderr, "%s\n", msg);
return (0);


See environ(7) for descriptions of the following environment variables
that affect the execution of yacc: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES,

yacc can handle characters from EUC primary and supplementary codesets as
one-token symbols. EUC codes can only be single character quoted terminal
symbols. yacc expects yylex() to return a wide character (wchar_t) value
for these one-token symbols.


The following exit values are returned:

Successful completion.

An error occurred.


state transitions of the generated parser

source code of the generated parser

header file for the generated parser

temporary file

temporary file

temporary file

parser prototype for C programs


See attributes(7) for descriptions of the following attributes:

|Interface Stability | Committed |
|Standard | See standards(7). |


lex(1), attributes(7), environ(7), standards(7)


The number of reduce-reduce and shift-reduce conflicts is reported on the
standard error output. A more detailed report is found in the y.output
file. Similarly, if some rules are not reachable from the start symbol,
this instance is also reported.


Because file names are fixed, at most one yacc process can be active in a
given directory at a given time.

Users are encouraged to avoid using $ as part of any identifier name.

August 24, 2009 YACC(1)