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YACC(1) General Commands Manual YACC(1)

yaccan LALR(1) parser generator

yacc [-dlrtv] [-b file_prefix] [-o output_file] [-p symbol_prefix] file

yacc reads the grammar specification in file and generates an LR(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

The options are as follows:

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.
The -d option causes the header file to be written.
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.
The -o option specifies an explicit name for the parser's output file name instead of the default. The names of the other output files are constructed from output_file as described under the -d and -v options.
The -p option changes the prefix prepended to yacc-generated symbols to the string denoted by symbol_prefix. The default prefix is the string yy.
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 -t option changes the preprocessor directives generated by yacc so that debugging statements will be incorporated in the compiled code.
The -v option causes a human-readable description of the generated parser to be written to the file y.output.

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.


The yacc utility exits 0 on success, and >0 if an error occurs.

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.


S. C. Johnson, Yacc — Yet Another Compiler-Compiler, AT&T Bell Laboratories, Computing Science Technical Report, 32, July 1975.

F. DeRemer and T. J. Pennello, Efficient Computation of LALR(1) Look-Ahead Sets, TOPLAS, Issue 4, Volume 4, pp. 615–649, 1982.

The yacc utility is compliant with the IEEE Std 1003.1-2008 (“POSIX.1”) specification, though its presence is optional.

The flags [-or] are extensions to that specification.

yacc was originally developed at AT&T by Stephen C. Johnson.

Berkeley yacc was originally developed using PCC on a VAX with the intent of being as compatible as possible with AT&T UNIX yacc. Much is owed to the unflagging efforts of Keith Bostic. His badgering kept me working on yacc long after I was ready to quit.

Berkeley yacc is based on the excellent algorithm for computing LALR(1) lookaheads developed by Tom Pennello and Frank DeRemer. The algorithm is described in their almost impenetrable article in TOPLAS (see above).

Finally, much credit must go to those who pointed out deficiencies of earlier releases. Among the most prolific contributors were Benson I. Margulies, Dave Gentzel, Antoine Verheijen, Peter S. Housel, Dale Smith, Ozan Yigit, John Campbell, Bill Sommerfeld, Paul Hilfinger, Gary Bridgewater, Dave Bakken, Dan Lanciani, Richard Sargent, and Parag Patel.

The yacc utility was written by Robert Corbett.

March 8, 2021 OpenBSD-current