Documentation/technical/api-parse-options.txt - jrn/git - Git at Google

 parse-options API
 =================

 The parse-options API is used to parse and massage options in Git
 and to provide a usage help with consistent look.

 Basics
 ------

 The argument vector `argv[]` may usually contain mandatory or optional
 'non-option arguments', e.g. a filename or a branch, and 'options'.
 Options are optional arguments that start with a dash and
 that allow to change the behavior of a command.

 * There are basically three types of options:
   'boolean' options,
   options with (mandatory) 'arguments' and
   options with 'optional arguments'
   (i.e. a boolean option that can be adjusted).

 * There are basically two forms of options:
   'Short options' consist of one dash (`-`) and one alphanumeric
   character.
   'Long options' begin with two dashes (`--`) and some
   alphanumeric characters.

 * Options are case-sensitive.
   Please define 'lower-case long options' only.

 The parse-options API allows:

 * 'stuck' and 'separate form' of options with arguments.
   `-oArg` is stuck, `-o Arg` is separate form.
   `--option=Arg` is stuck, `--option Arg` is separate form.

 * Long options may be 'abbreviated', as long as the abbreviation
   is unambiguous.

 * Short options may be bundled, e.g. `-a -b` can be specified as `-ab`.

 * Boolean long options can be 'negated' (or 'unset') by prepending
   `no-`, e.g. `--no-abbrev` instead of `--abbrev`. Conversely,
   options that begin with `no-` can be 'negated' by removing it.
   Other long options can be unset (e.g., set string to NULL, set
   integer to 0) by prepending `no-`.

 * Options and non-option arguments can clearly be separated using the `--`
   option, e.g. `-a -b --option -- --this-is-a-file` indicates that
   `--this-is-a-file` must not be processed as an option.

 Steps to parse options
 ----------------------

 . `#include "parse-options.h"`

 . define a NULL-terminated
   `static const char * const builtin_foo_usage[]` array
   containing alternative usage strings

 . define `builtin_foo_options` array as described below
   in section 'Data Structure'.

 . in `cmd_foo(int argc, const char **argv, const char *prefix)`
   call

 	argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags);
 +
 `parse_options()` will filter out the processed options of `argv[]` and leave the
 non-option arguments in `argv[]`.
 `argc` is updated appropriately because of the assignment.
 +
 You can also pass NULL instead of a usage array as the fifth parameter of
 parse_options(), to avoid displaying a help screen with usage info and
 option list.  This should only be done if necessary, e.g. to implement
 a limited parser for only a subset of the options that needs to be run
 before the full parser, which in turn shows the full help message.
 +
 Flags are the bitwise-or of:

 `PARSE_OPT_KEEP_DASHDASH`::
 	Keep the `--` that usually separates options from
 	non-option arguments.

 `PARSE_OPT_STOP_AT_NON_OPTION`::
 	Usually the whole argument vector is massaged and reordered.
 	Using this flag, processing is stopped at the first non-option
 	argument.

 `PARSE_OPT_KEEP_ARGV0`::
 	Keep the first argument, which contains the program name.  It's
 	removed from argv[] by default.

 `PARSE_OPT_KEEP_UNKNOWN`::
 	Keep unknown arguments instead of erroring out.  This doesn't
 	work for all combinations of arguments as users might expect
 	it to do.  E.g. if the first argument in `--unknown --known`
 	takes a value (which we can't know), the second one is
 	mistakenly interpreted as a known option.  Similarly, if
 	`PARSE_OPT_STOP_AT_NON_OPTION` is set, the second argument in
 	`--unknown value` will be mistakenly interpreted as a
 	non-option, not as a value belonging to the unknown option,
 	the parser early.  That's why parse_options() errors out if
 	both options are set.

 `PARSE_OPT_NO_INTERNAL_HELP`::
 	By default, parse_options() handles `-h`, `--help` and
 	`--help-all` internally, by showing a help screen.  This option
 	turns it off and allows one to add custom handlers for these
 	options, or to just leave them unknown.

 Data Structure
 --------------

 The main data structure is an array of the `option` struct,
 say `static struct option builtin_add_options[]`.
 There are some macros to easily define options:

 `OPT__ABBREV(&int_var)`::
 	Add `--abbrev[=<n>]`.

 `OPT__COLOR(&int_var, description)`::
 	Add `--color[=<when>]` and `--no-color`.

 `OPT__DRY_RUN(&int_var, description)`::
 	Add `-n, --dry-run`.

 `OPT__FORCE(&int_var, description)`::
 	Add `-f, --force`.

 `OPT__QUIET(&int_var, description)`::
 	Add `-q, --quiet`.

 `OPT__VERBOSE(&int_var, description)`::
 	Add `-v, --verbose`.

 `OPT_GROUP(description)`::
 	Start an option group. `description` is a short string that
 	describes the group or an empty string.
 	Start the description with an upper-case letter.

 `OPT_BOOL(short, long, &int_var, description)`::
 	Introduce a boolean option. `int_var` is set to one with
 	`--option` and set to zero with `--no-option`.

 `OPT_COUNTUP(short, long, &int_var, description)`::
 	Introduce a count-up option.
 	Each use of `--option` increments `int_var`, starting from zero
 	(even if initially negative), and `--no-option` resets it to
 	zero. To determine if `--option` or `--no-option` was encountered at
 	all, initialize `int_var` to a negative value, and if it is still
 	negative after parse_options(), then neither `--option` nor
 	`--no-option` was seen.

 `OPT_BIT(short, long, &int_var, description, mask)`::
 	Introduce a boolean option.
 	If used, `int_var` is bitwise-ored with `mask`.

 `OPT_NEGBIT(short, long, &int_var, description, mask)`::
 	Introduce a boolean option.
 	If used, `int_var` is bitwise-anded with the inverted `mask`.

 `OPT_SET_INT(short, long, &int_var, description, integer)`::
 	Introduce an integer option.
 	`int_var` is set to `integer` with `--option`, and
 	reset to zero with `--no-option`.

 `OPT_STRING(short, long, &str_var, arg_str, description)`::
 	Introduce an option with string argument.
 	The string argument is put into `str_var`.

 `OPT_STRING_LIST(short, long, &struct string_list, arg_str, description)`::
 	Introduce an option with string argument.
 	The string argument is stored as an element in `string_list`.
 	Use of `--no-option` will clear the list of preceding values.

 `OPT_INTEGER(short, long, &int_var, description)`::
 	Introduce an option with integer argument.
 	The integer is put into `int_var`.

 `OPT_MAGNITUDE(short, long, &unsigned_long_var, description)`::
 	Introduce an option with a size argument. The argument must be a
 	non-negative integer and may include a suffix of 'k', 'm' or 'g' to
 	scale the provided value by 1024, 1024^2 or 1024^3 respectively.
 	The scaled value is put into `unsigned_long_var`.

 `OPT_EXPIRY_DATE(short, long, &timestamp_t_var, description)`::
 	Introduce an option with expiry date argument, see `parse_expiry_date()`.
 	The timestamp is put into `timestamp_t_var`.

 `OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`::
 	Introduce an option with argument.
 	The argument will be fed into the function given by `func_ptr`
 	and the result will be put into `var`.
 	See 'Option Callbacks' below for a more elaborate description.

 `OPT_FILENAME(short, long, &var, description)`::
 	Introduce an option with a filename argument.
 	The filename will be prefixed by passing the filename along with
 	the prefix argument of `parse_options()` to `prefix_filename()`.

 `OPT_ARGUMENT(long, description)`::
 	Introduce a long-option argument that will be kept in `argv[]`.

 `OPT_NUMBER_CALLBACK(&var, description, func_ptr)`::
 	Recognize numerical options like -123 and feed the integer as
 	if it was an argument to the function given by `func_ptr`.
 	The result will be put into `var`.  There can be only one such
 	option definition.  It cannot be negated and it takes no
 	arguments.  Short options that happen to be digits take
 	precedence over it.

 `OPT_COLOR_FLAG(short, long, &int_var, description)`::
 	Introduce an option that takes an optional argument that can
 	have one of three values: "always", "never", or "auto".  If the
 	argument is not given, it defaults to "always".  The `--no-` form
 	works like `--long=never`; it cannot take an argument.  If
 	"always", set `int_var` to 1; if "never", set `int_var` to 0; if
 	"auto", set `int_var` to 1 if stdout is a tty or a pager,
 	0 otherwise.

 `OPT_NOOP_NOARG(short, long)`::
 	Introduce an option that has no effect and takes no arguments.
 	Use it to hide deprecated options that are still to be recognized
 	and ignored silently.

 `OPT_PASSTHRU(short, long, &char_var, arg_str, description, flags)`::
 	Introduce an option that will be reconstructed into a char* string,
 	which must be initialized to NULL. This is useful when you need to
 	pass the command-line option to another command. Any previous value
 	will be overwritten, so this should only be used for options where
 	the last one specified on the command line wins.

 `OPT_PASSTHRU_ARGV(short, long, &argv_array_var, arg_str, description, flags)`::
 	Introduce an option where all instances of it on the command-line will
 	be reconstructed into an argv_array. This is useful when you need to
 	pass the command-line option, which can be specified multiple times,
 	to another command.

 `OPT_CMDMODE(short, long, &int_var, description, enum_val)`::
 	Define an "operation mode" option, only one of which in the same
 	group of "operating mode" options that share the same `int_var`
 	can be given by the user. `enum_val` is set to `int_var` when the
 	option is used, but an error is reported if other "operating mode"
 	option has already set its value to the same `int_var`.


 The last element of the array must be `OPT_END()`.

 If not stated otherwise, interpret the arguments as follows:

 * `short` is a character for the short option
   (e.g. `'e'` for `-e`, use `0` to omit),

 * `long` is a string for the long option
   (e.g. `"example"` for `--example`, use `NULL` to omit),

 * `int_var` is an integer variable,

 * `str_var` is a string variable (`char *`),

 * `arg_str` is the string that is shown as argument
   (e.g. `"branch"` will result in `<branch>`).
   If set to `NULL`, three dots (`...`) will be displayed.

 * `description` is a short string to describe the effect of the option.
   It shall begin with a lower-case letter and a full stop (`.`) shall be
   omitted at the end.

 Option Callbacks
 ----------------

 The function must be defined in this form:

 	int func(const struct option *opt, const char *arg, int unset)

 The callback mechanism is as follows:

 * Inside `func`, the only interesting member of the structure
   given by `opt` is the void pointer `opt->value`.
   `*opt->value` will be the value that is saved into `var`, if you
   use `OPT_CALLBACK()`.
   For example, do `*(unsigned long *)opt->value = 42;` to get 42
   into an `unsigned long` variable.

 * Return value `0` indicates success and non-zero return
   value will invoke `usage_with_options()` and, thus, die.

 * If the user negates the option, `arg` is `NULL` and `unset` is 1.

 Sophisticated option parsing
 ----------------------------

 If you need, for example, option callbacks with optional arguments
 or without arguments at all, or if you need other special cases,
 that are not handled by the macros above, you need to specify the
 members of the `option` structure manually.

 This is not covered in this document, but well documented
 in `parse-options.h` itself.

 Examples
 --------

 See `test-parse-options.c` and
 `builtin/add.c`,
 `builtin/clone.c`,
 `builtin/commit.c`,
 `builtin/fetch.c`,
 `builtin/fsck.c`,
 `builtin/rm.c`
 for real-world examples.
	parse-options API
	=================

	The parse-options API is used to parse and massage options in Git
	and to provide a usage help with consistent look.

	Basics
	------

	The argument vector `argv[]` may usually contain mandatory or optional
	'non-option arguments', e.g. a filename or a branch, and 'options'.
	Options are optional arguments that start with a dash and
	that allow to change the behavior of a command.

	* There are basically three types of options:
	'boolean' options,
	options with (mandatory) 'arguments' and
	options with 'optional arguments'
	(i.e. a boolean option that can be adjusted).

	* There are basically two forms of options:
	'Short options' consist of one dash (`-`) and one alphanumeric
	character.
	'Long options' begin with two dashes (`--`) and some
	alphanumeric characters.

	* Options are case-sensitive.
	Please define 'lower-case long options' only.

	The parse-options API allows:

	* 'stuck' and 'separate form' of options with arguments.
	`-oArg` is stuck, `-o Arg` is separate form.
	`--option=Arg` is stuck, `--option Arg` is separate form.

	* Long options may be 'abbreviated', as long as the abbreviation
	is unambiguous.

	* Short options may be bundled, e.g. `-a -b` can be specified as `-ab`.

	* Boolean long options can be 'negated' (or 'unset') by prepending
	`no-`, e.g. `--no-abbrev` instead of `--abbrev`. Conversely,
	options that begin with `no-` can be 'negated' by removing it.
	Other long options can be unset (e.g., set string to NULL, set
	integer to 0) by prepending `no-`.

	* Options and non-option arguments can clearly be separated using the `--`
	option, e.g. `-a -b --option -- --this-is-a-file` indicates that
	`--this-is-a-file` must not be processed as an option.

	Steps to parse options
	----------------------

	. `#include "parse-options.h"`

	. define a NULL-terminated
	`static const char * const builtin_foo_usage[]` array
	containing alternative usage strings

	. define `builtin_foo_options` array as described below
	in section 'Data Structure'.

	. in `cmd_foo(int argc, const char *argv, const char prefix)`
	call

	argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags);
	+
	`parse_options()` will filter out the processed options of `argv[]` and leave the
	non-option arguments in `argv[]`.
	`argc` is updated appropriately because of the assignment.
	+
	You can also pass NULL instead of a usage array as the fifth parameter of
	parse_options(), to avoid displaying a help screen with usage info and
	option list. This should only be done if necessary, e.g. to implement
	a limited parser for only a subset of the options that needs to be run
	before the full parser, which in turn shows the full help message.
	+
	Flags are the bitwise-or of:

	`PARSE_OPT_KEEP_DASHDASH`::
	Keep the `--` that usually separates options from
	non-option arguments.

	`PARSE_OPT_STOP_AT_NON_OPTION`::
	Usually the whole argument vector is massaged and reordered.
	Using this flag, processing is stopped at the first non-option
	argument.

	`PARSE_OPT_KEEP_ARGV0`::
	Keep the first argument, which contains the program name. It's
	removed from argv[] by default.

	`PARSE_OPT_KEEP_UNKNOWN`::
	Keep unknown arguments instead of erroring out. This doesn't
	work for all combinations of arguments as users might expect
	it to do. E.g. if the first argument in `--unknown --known`
	takes a value (which we can't know), the second one is
	mistakenly interpreted as a known option. Similarly, if
	`PARSE_OPT_STOP_AT_NON_OPTION` is set, the second argument in
	`--unknown value` will be mistakenly interpreted as a
	non-option, not as a value belonging to the unknown option,
	the parser early. That's why parse_options() errors out if
	both options are set.

	`PARSE_OPT_NO_INTERNAL_HELP`::
	By default, parse_options() handles `-h`, `--help` and
	`--help-all` internally, by showing a help screen. This option
	turns it off and allows one to add custom handlers for these
	options, or to just leave them unknown.

	Data Structure
	--------------

	The main data structure is an array of the `option` struct,
	say `static struct option builtin_add_options[]`.
	There are some macros to easily define options:

	`OPT__ABBREV(&int_var)`::
	Add `--abbrev[=<n>]`.

	`OPT__COLOR(&int_var, description)`::
	Add `--color[=<when>]` and `--no-color`.

	`OPT__DRY_RUN(&int_var, description)`::
	Add `-n, --dry-run`.

	`OPT__FORCE(&int_var, description)`::
	Add `-f, --force`.

	`OPT__QUIET(&int_var, description)`::
	Add `-q, --quiet`.

	`OPT__VERBOSE(&int_var, description)`::
	Add `-v, --verbose`.

	`OPT_GROUP(description)`::
	Start an option group. `description` is a short string that
	describes the group or an empty string.
	Start the description with an upper-case letter.

	`OPT_BOOL(short, long, &int_var, description)`::
	Introduce a boolean option. `int_var` is set to one with
	`--option` and set to zero with `--no-option`.

	`OPT_COUNTUP(short, long, &int_var, description)`::
	Introduce a count-up option.
	Each use of `--option` increments `int_var`, starting from zero
	(even if initially negative), and `--no-option` resets it to
	zero. To determine if `--option` or `--no-option` was encountered at
	all, initialize `int_var` to a negative value, and if it is still
	negative after parse_options(), then neither `--option` nor
	`--no-option` was seen.

	`OPT_BIT(short, long, &int_var, description, mask)`::
	Introduce a boolean option.
	If used, `int_var` is bitwise-ored with `mask`.

	`OPT_NEGBIT(short, long, &int_var, description, mask)`::
	Introduce a boolean option.
	If used, `int_var` is bitwise-anded with the inverted `mask`.

	`OPT_SET_INT(short, long, &int_var, description, integer)`::
	Introduce an integer option.
	`int_var` is set to `integer` with `--option`, and
	reset to zero with `--no-option`.

	`OPT_STRING(short, long, &str_var, arg_str, description)`::
	Introduce an option with string argument.
	The string argument is put into `str_var`.

	`OPT_STRING_LIST(short, long, &struct string_list, arg_str, description)`::
	Introduce an option with string argument.
	The string argument is stored as an element in `string_list`.
	Use of `--no-option` will clear the list of preceding values.

	`OPT_INTEGER(short, long, &int_var, description)`::
	Introduce an option with integer argument.
	The integer is put into `int_var`.

	`OPT_MAGNITUDE(short, long, &unsigned_long_var, description)`::
	Introduce an option with a size argument. The argument must be a
	non-negative integer and may include a suffix of 'k', 'm' or 'g' to
	scale the provided value by 1024, 1024^2 or 1024^3 respectively.
	The scaled value is put into `unsigned_long_var`.

	`OPT_EXPIRY_DATE(short, long, &timestamp_t_var, description)`::
	Introduce an option with expiry date argument, see `parse_expiry_date()`.
	The timestamp is put into `timestamp_t_var`.

	`OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`::
	Introduce an option with argument.
	The argument will be fed into the function given by `func_ptr`
	and the result will be put into `var`.
	See 'Option Callbacks' below for a more elaborate description.

	`OPT_FILENAME(short, long, &var, description)`::
	Introduce an option with a filename argument.
	The filename will be prefixed by passing the filename along with
	the prefix argument of `parse_options()` to `prefix_filename()`.

	`OPT_ARGUMENT(long, description)`::
	Introduce a long-option argument that will be kept in `argv[]`.

	`OPT_NUMBER_CALLBACK(&var, description, func_ptr)`::
	Recognize numerical options like -123 and feed the integer as
	if it was an argument to the function given by `func_ptr`.
	The result will be put into `var`. There can be only one such
	option definition. It cannot be negated and it takes no
	arguments. Short options that happen to be digits take
	precedence over it.

	`OPT_COLOR_FLAG(short, long, &int_var, description)`::
	Introduce an option that takes an optional argument that can
	have one of three values: "always", "never", or "auto". If the
	argument is not given, it defaults to "always". The `--no-` form
	works like `--long=never`; it cannot take an argument. If
	"always", set `int_var` to 1; if "never", set `int_var` to 0; if
	"auto", set `int_var` to 1 if stdout is a tty or a pager,
	0 otherwise.

	`OPT_NOOP_NOARG(short, long)`::
	Introduce an option that has no effect and takes no arguments.
	Use it to hide deprecated options that are still to be recognized
	and ignored silently.

	`OPT_PASSTHRU(short, long, &char_var, arg_str, description, flags)`::
	Introduce an option that will be reconstructed into a char* string,
	which must be initialized to NULL. This is useful when you need to
	pass the command-line option to another command. Any previous value
	will be overwritten, so this should only be used for options where
	the last one specified on the command line wins.

	`OPT_PASSTHRU_ARGV(short, long, &argv_array_var, arg_str, description, flags)`::
	Introduce an option where all instances of it on the command-line will
	be reconstructed into an argv_array. This is useful when you need to
	pass the command-line option, which can be specified multiple times,
	to another command.

	`OPT_CMDMODE(short, long, &int_var, description, enum_val)`::
	Define an "operation mode" option, only one of which in the same
	group of "operating mode" options that share the same `int_var`
	can be given by the user. `enum_val` is set to `int_var` when the
	option is used, but an error is reported if other "operating mode"
	option has already set its value to the same `int_var`.


	The last element of the array must be `OPT_END()`.

	If not stated otherwise, interpret the arguments as follows:

	* `short` is a character for the short option
	(e.g. `'e'` for `-e`, use `0` to omit),

	* `long` is a string for the long option
	(e.g. `"example"` for `--example`, use `NULL` to omit),

	* `int_var` is an integer variable,

	* `str_var` is a string variable (`char *`),

	* `arg_str` is the string that is shown as argument
	(e.g. `"branch"` will result in `<branch>`).
	If set to `NULL`, three dots (`...`) will be displayed.

	* `description` is a short string to describe the effect of the option.
	It shall begin with a lower-case letter and a full stop (`.`) shall be
	omitted at the end.

	Option Callbacks
	----------------

	The function must be defined in this form:

	int func(const struct option opt, const char arg, int unset)

	The callback mechanism is as follows:

	* Inside `func`, the only interesting member of the structure
	given by `opt` is the void pointer `opt->value`.
	`*opt->value` will be the value that is saved into `var`, if you
	use `OPT_CALLBACK()`.
	For example, do `(unsigned long )opt->value = 42;` to get 42
	into an `unsigned long` variable.

	* Return value `0` indicates success and non-zero return
	value will invoke `usage_with_options()` and, thus, die.

	* If the user negates the option, `arg` is `NULL` and `unset` is 1.

	Sophisticated option parsing
	----------------------------

	If you need, for example, option callbacks with optional arguments
	or without arguments at all, or if you need other special cases,
	that are not handled by the macros above, you need to specify the
	members of the `option` structure manually.

	This is not covered in this document, but well documented
	in `parse-options.h` itself.

	Examples
	--------

	See `test-parse-options.c` and
	`builtin/add.c`,
	`builtin/clone.c`,
	`builtin/commit.c`,
	`builtin/fetch.c`,
	`builtin/fsck.c`,
	`builtin/rm.c`
	for real-world examples.