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, options, and subcommands. 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.

Subcommands are special in a couple of ways:

  • Subcommands only have long form, and they have no double dash prefix, no negated form, and no description, and they don’t take any arguments, and can’t be abbreviated.

  • There must be exactly one subcommand among the arguments, or zero if the command has a default operation mode.

  • All arguments following the subcommand are considered to be arguments of the subcommand, and, conversely, arguments meant for the subcommand may not precede the subcommand.

Therefore, if the options array contains at least one subcommand and parse_options() encounters the first dashless argument, it will either:

  • stop and return, if that dashless argument is a known subcommand, setting value to the function pointer associated with that subcommand, storing the name of the subcommand in argv[0], and leaving the rest of the arguments unprocessed, or

  • stop and return, if it was invoked with the PARSE_OPT_SUBCOMMAND_OPTIONAL flag and that dashless argument doesn’t match any subcommands, leaving value unchanged and the rest of the arguments unprocessed, or

  • show error and usage, and abort.

Steps to parse options

  1. #include "parse-options.h"

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

  3. define builtin_foo_options array as described below in section Data Structure.

  4. 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_OPT

    Keep unknown options 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. Note that non-option arguments are always kept, even without this flag.

    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.

    PARSE_OPT_SUBCOMMAND_OPTIONAL

    Don’t error out when no subcommand is specified.

Note that PARSE_OPT_STOP_AT_NON_OPTION is incompatible with subcommands; while PARSE_OPT_KEEP_DASHDASH and PARSE_OPT_KEEP_UNKNOWN_OPT can only be used with subcommands when combined with PARSE_OPT_SUBCOMMAND_OPTIONAL.

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, 10242 or 10243 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_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, &strvec_var, arg_str, description, flags)

Introduce an option where all instances of it on the command-line will be reconstructed into a strvec. 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. int_var is set to enum_val 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. In new commands consider using subcommands instead.

OPT_SUBCOMMAND(long, &fn_ptr, subcommand_fn)

Define a subcommand. subcommand_fn is put into fn_ptr when this subcommand is used.

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.