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9.1 Bison Options

Bison supports both traditional single-letter options and mnemonic long option names. Long option names are indicated with ‘--’ instead of ‘-’. Abbreviations for option names are allowed as long as they are unique. When a long option takes an argument, like ‘--file-prefix’, connect the option name and the argument with ‘=’.

Here is a list of options that can be used with Bison, alphabetized by short option. It is followed by a cross key alphabetized by long option.

Operations modes:

-h
--help
Print a summary of the command-line options to Bison and exit.
-V
--version
Print the version number of Bison and exit.
--print-localedir
Print the name of the directory containing locale-dependent data.
--print-datadir
Print the name of the directory containing skeletons and XSLT.
-y
--yacc
Act more like the traditional Yacc command. This can cause different diagnostics to be generated, and may change behavior in other minor ways. Most importantly, imitate Yacc's output file name conventions, so that the parser implementation file is called y.tab.c, and the other outputs are called y.output and y.tab.h. Also, if generating a deterministic parser in C, generate #define statements in addition to an enum to associate token numbers with token names. Thus, the following shell script can substitute for Yacc, and the Bison distribution contains such a script for compatibility with POSIX:
          #! /bin/sh
          bison -y "$@"

The -y/--yacc option is intended for use with traditional Yacc grammars. If your grammar uses a Bison extension like ‘%glr-parser’, Bison might not be Yacc-compatible even if this option is specified.

-W [category]
--warnings[=category]
Output warnings falling in category. category can be one of:
midrule-values
Warn about mid-rule values that are set but not used within any of the actions of the parent rule. For example, warn about unused $2 in:
               exp: '1' { $$ = 1; } '+' exp { $$ = $1 + $4; };

Also warn about mid-rule values that are used but not set. For example, warn about unset $$ in the mid-rule action in:

               exp: '1' { $1 = 1; } '+' exp { $$ = $2 + $4; };

These warnings are not enabled by default since they sometimes prove to be false alarms in existing grammars employing the Yacc constructs $0 or $-n (where n is some positive integer).

yacc
Incompatibilities with POSIX Yacc.
conflicts-sr
conflicts-rr
S/R and R/R conflicts. These warnings are enabled by default. However, if the %expect or %expect-rr directive is specified, an unexpected number of conflicts is an error, and an expected number of conflicts is not reported, so -W and --warning then have no effect on the conflict report.
deprecated
Deprecated constructs whose support will be removed in future versions of Bison.
empty-rule
Empty rules without %empty. See Empty Rules. Disabled by default, but enabled by uses of %empty, unless -Wno-empty-rule was specified.
precedence
Useless precedence and associativity directives. Disabled by default.

Consider for instance the following grammar:

               %nonassoc "="
               %left "+"
               %left "*"
               %precedence "("
               %%
               stmt:
                 exp
               | "var" "=" exp
               ;
               
               exp:
                 exp "+" exp
               | exp "*" "num"
               | "(" exp ")"
               | "num"
               ;

Bison reports:

               warning: useless precedence and associativity for "="
                %nonassoc "="
                          ^^^
               warning: useless associativity for "*", use %precedence
                %left "*"
                      ^^^
               warning: useless precedence for "("
                %precedence "("
                            ^^^

One would get the exact same parser with the following directives instead:

               %left "+"
               %precedence "*"

other
All warnings not categorized above. These warnings are enabled by default.

This category is provided merely for the sake of completeness. Future releases of Bison may move warnings from this category to new, more specific categories.

all
All the warnings except yacc.
none
Turn off all the warnings.
error
See -Werror, below.

A category can be turned off by prefixing its name with ‘no-’. For instance, -Wno-yacc will hide the warnings about POSIX Yacc incompatibilities.

-Werror
Turn enabled warnings for every category into errors, unless they are explicitly disabled by -Wno-error=category.
-Werror=category
Enable warnings falling in category, and treat them as errors.

category is the same as for --warnings, with the exception that it may not be prefixed with ‘no-’ (see above).

Note that the precedence of the ‘=’ and ‘,’ operators is such that the following commands are not equivalent, as the first will not treat S/R conflicts as errors.

          $ bison -Werror=yacc,conflicts-sr input.y
          $ bison -Werror=yacc,error=conflicts-sr input.y

-Wno-error
Do not turn enabled warnings for every category into errors, unless they are explicitly enabled by -Werror=category.
-Wno-error=category
Deactivate the error treatment for this category. However, the warning itself won't be disabled, or enabled, by this option.
-f [feature]
--feature[=feature]
Activate miscellaneous feature. feature can be one of:
caret
diagnostics-show-caret
Show caret errors, in a manner similar to GCC's -fdiagnostics-show-caret, or Clang's -fcaret-diagnotics. The location provided with the message is used to quote the corresponding line of the source file, underlining the important part of it with carets (^). Here is an example, using the following file in.y:
               %type <ival> exp
               %%
               exp: exp '+' exp { $exp = $1 + $2; };

When invoked with -fcaret (or nothing), Bison will report:

               in.y:3.20-23: error: ambiguous reference: '$exp'
                exp: exp '+' exp { $exp = $1 + $2; };
                                   ^^^^
               in.y:3.1-3:       refers to: $exp at $$
                exp: exp '+' exp { $exp = $1 + $2; };
                ^^^
               in.y:3.6-8:       refers to: $exp at $1
                exp: exp '+' exp { $exp = $1 + $2; };
                     ^^^
               in.y:3.14-16:     refers to: $exp at $3
                exp: exp '+' exp { $exp = $1 + $2; };
                             ^^^
               in.y:3.32-33: error: $2 of 'exp' has no declared type
                exp: exp '+' exp { $exp = $1 + $2; };
                                               ^^

Whereas, when invoked with -fno-caret, Bison will only report:

               in.y:3.20-23: error: ambiguous reference: ‘$exp’
               in.y:3.1-3:       refers to: $exp at $$
               in.y:3.6-8:       refers to: $exp at $1
               in.y:3.14-16:     refers to: $exp at $3
               in.y:3.32-33: error: $2 of ‘exp’ has no declared type

This option is activated by default.

Tuning the parser:

-t
--debug
In the parser implementation file, define the macro YYDEBUG to 1 if it is not already defined, so that the debugging facilities are compiled. See Tracing Your Parser.
-D name[=value]
--define=name[=value]
-F name[=value]
--force-define=name[=value]
Each of these is equivalent to ‘%define name "value"’ (see %define Summary) except that Bison processes multiple definitions for the same name as follows:

You should avoid using -F and --force-define in your make files unless you are confident that it is safe to quietly ignore any conflicting %define that may be added to the grammar file.

-L language
--language=language
Specify the programming language for the generated parser, as if %language was specified (see Bison Declaration Summary). Currently supported languages include C, C++, and Java. language is case-insensitive.
--locations
Pretend that %locations was specified. See Decl Summary.
-p prefix
--name-prefix=prefix
Pretend that %name-prefix "prefix" was specified (see Decl Summary). Obsoleted by -Dapi.prefix=prefix. See Multiple Parsers in the Same Program.
-l
--no-lines
Don't put any #line preprocessor commands in the parser implementation file. Ordinarily Bison puts them in the parser implementation file so that the C compiler and debuggers will associate errors with your source file, the grammar file. This option causes them to associate errors with the parser implementation file, treating it as an independent source file in its own right.
-S file
--skeleton=file
Specify the skeleton to use, similar to %skeleton (see Bison Declaration Summary).

If file does not contain a /, file is the name of a skeleton file in the Bison installation directory. If it does, file is an absolute file name or a file name relative to the current working directory. This is similar to how most shells resolve commands.

-k
--token-table
Pretend that %token-table was specified. See Decl Summary.

Adjust the output:

--defines[=file]
Pretend that %defines was specified, i.e., write an extra output file containing macro definitions for the token type names defined in the grammar, as well as a few other declarations. See Decl Summary.
-d
This is the same as --defines except -d does not accept a file argument since POSIX Yacc requires that -d can be bundled with other short options.
-b file-prefix
--file-prefix=prefix
Pretend that %file-prefix was specified, i.e., specify prefix to use for all Bison output file names. See Decl Summary.
-r things
--report=things
Write an extra output file containing verbose description of the comma separated list of things among:
state
Description of the grammar, conflicts (resolved and unresolved), and parser's automaton.
itemset
Implies state and augments the description of the automaton with the full set of items for each state, instead of its core only.
lookahead
Implies state and augments the description of the automaton with each rule's lookahead set.
solved
Implies state. Explain how conflicts were solved thanks to precedence and associativity directives.
all
Enable all the items.
none
Do not generate the report.

--report-file=file
Specify the file for the verbose description.
-v
--verbose
Pretend that %verbose was specified, i.e., write an extra output file containing verbose descriptions of the grammar and parser. See Decl Summary.
-o file
--output=file
Specify the file for the parser implementation file.

The other output files' names are constructed from file as described under the ‘-v’ and ‘-d’ options.

-g [file]
--graph[=file]
Output a graphical representation of the parser's automaton computed by Bison, in Graphviz DOT format. file is optional. If omitted and the grammar file is foo.y, the output file will be foo.dot.
-x [file]
--xml[=file]
Output an XML report of the parser's automaton computed by Bison. file is optional. If omitted and the grammar file is foo.y, the output file will be foo.xml. (The current XML schema is experimental and may evolve. More user feedback will help to stabilize it.)