yacc -- yet another compiler-compiler


yacc [-vVcdltw] [-P driver_file] [-b file_prefix] [-p sym_prefix] [-Q[y|n]] file


The yacc command converts a context-free grammar into a set of tables for a simple automaton that executes a Look Ahead Left-to-Right (LALR (1)) parsing algorithm. The grammar may be ambiguous; specified precedence rules are used to break ambiguities. yacc processes supplementary code set characters in program comments and strings, and single-byte supplementary code set characters in tokens, according to the locale specified in the LC_CTYPE environment variable (see LANG on environ(5)).

The output file,, must be compiled by the C compiler to produce a program 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.

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

-b file_prefix
Change to use file_prefix instead of y as the prefix for the output filenames.

Causes extern "C" { ... } to surround the C++ only declarations of the functions yyerror, yylex, and yyparse.

Generates the file with the #define statements that associate the yacc-assigned ``token codes'' with the user-declared ``token names.'' This association allows source files other than to access the token codes.

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

-P driver_file
Supplies the path name of an alternate parser prototype.

-p sym_prefix
Change to use sym_prefix instead of yy as the prefix for the external linkage names.

The -Qy option puts the version stamping information in 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 under conditional compilation control. By default, this code is not included when 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 zero, then the code will not be included. The size and execution time of a program produced without the runtime debugging code will be smaller and slightly faster.

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

Generates writable yacc tables. These tables are read-only by default.


defines for token names

yacc.tmp, yacc.debug, yacc.acts
temporary files

parser prototype for C programs

usually /usr/ccs/lib

language-specific message file. (See LANG on environ(5).)


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 without -b or with the same -b prefix can be active in a given directory at a given time.


environ(5), lex(1)
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004