YACC(1) BSD General Commands Manual YACC(1)NAMEyacc — an LALR(1) parser generator
SYNOPSISyacc [-dgilPrtVv] [-b prefix] [-o outputfile] [-p symbol_prefix] filename
DESCRIPTIONyacc 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) pars‐
ing 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 prefix The -b option changes the prefix prepended to the output
file names to the string denoted by prefix. The default
prefix is the character y.
-d The -d option causes the header file y.tab.h to be written.
It contains #define's for the token identifiers.
-g The -g option causes a graphical description of the gener‐
ated LALR(1) parser to be written to the file y.dot in
graphviz format, ready to be processed by dot(1).
-i The -i option causes a supplementary header file y.tab.i to
be written. It contains extern declarations and supplemen‐
tary #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 If the -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.
-o outputfile
The -o option specifies an explicit output file name should
be used instead of the default.
-P The -P options instructs yacc to create a reentrant parser,
like “%pure-parser” does.
-p symbol_prefix
The -p option changes the prefix prepended to yacc-gener‐
ated symbols to the string denoted by symbol_prefix. The
default prefix is the string yy.
-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 y.tab.c.
-t The -t option changes the preprocessor directives generated
by yacc so that debugging statements will be incorporated
in the compiled code.
-V The -V option prints the version number to the standard
output.
-v The -v option causes a human-readable description of the
generated parser to be written to the file y.output.
EXTENSIONSyacc provides some extensions for compatibility with bison(1) and other
implementations of yacc:
%expect number Tell yacc the expected number of shift/reduce con‐
flicts. That makes it only report the number if it
differs.
%expect-rr number Tell yacc the expected number of reduce/reduce con‐
flicts. That makes it only report the number if it
differs. This is (unlike bison(1)) allowable in
LALR(1) parsers.
%lex-param { argument-declaration }
By default, the lexer accepts no parameters, e.g.,
yylex(). Use this directive to add parameter declara‐
tions for your customized lexer.
%parse-param { argument-declaration }
By default, the parser accepts no parameters, e.g.,
yyparse(). Use this directive to add parameter decla‐
rations for your customized parser.
%pure-parser Most variables (other than yydebug and yynerrs) are
allocated on the stack within yyparse(), making the
parser reasonably reentrant.
ENVIRONMENT
The following environment variable is referenced by yacc:
TMPDIR If the environment variable TMPDIR is set, the string denoted by
TMPDIR will be used as the name of the directory where the tempo‐
rary files are created.
TABLES
The names of the tables generated by this version of 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.
FILES
y.code.c
y.tab.c
y.tab.h
y.output
/tmp/yacc.aXXXXXX
/tmp/yacc.tXXXXXX
/tmp/yacc.uXXXXXX
DIAGNOSTICS
If there are rules that are never reduced, the number of such rules is
written to the standard error. If there are any LALR(1) conflicts, the
number of conflicts is also written to the standard error.
STANDARDS
The yacc utility conforms to IEEE Std 1003.2 (“POSIX.2”).
BSD September 7, 2011 BSD
