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.

The parse-options API allows:

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

    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)

Add -n, \--dry-run.

OPT__QUIET(&int_var)

Add -q, \--quiet.

OPT__VERBOSE(&int_var)

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_BOOLEAN(short, long, &int_var, description)

Introduce a boolean option. int_var is incremented on each use.

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 a boolean option. If used, set int_var to integer.

OPT_SET_PTR(short, long, &ptr_var, description, ptr)

Introduce a boolean option. If used, set ptr_var to ptr.

OPT_STRING(short, long, &str_var, arg_str, description)

Introduce an option with string argument. The string argument is put into str_var.

OPT_INTEGER(short, long, &int_var, description)

Introduce an option with integer argument. The integer is put into int_var.

OPT_DATE(short, long, &int_var, description)

Introduce an option with date argument, see approxidate(). The timestamp is put into int_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.

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

If not stated otherwise, interpret the arguments as follows:

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:

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.