281 lines
9.5 KiB
Plaintext
281 lines
9.5 KiB
Plaintext
parse-options API
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=================
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The parse-options API is used to parse and massage options in Git
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and to provide a usage help with consistent look.
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Basics
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------
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The argument vector `argv[]` may usually contain mandatory or optional
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'non-option arguments', e.g. a filename or a branch, and 'options'.
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Options are optional arguments that start with a dash and
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that allow to change the behavior of a command.
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* There are basically three types of options:
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'boolean' options,
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options with (mandatory) 'arguments' and
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options with 'optional arguments'
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(i.e. a boolean option that can be adjusted).
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* There are basically two forms of options:
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'Short options' consist of one dash (`-`) and one alphanumeric
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character.
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'Long options' begin with two dashes (`--`) and some
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alphanumeric characters.
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* Options are case-sensitive.
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Please define 'lower-case long options' only.
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The parse-options API allows:
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* 'stuck' and 'separate form' of options with arguments.
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`-oArg` is stuck, `-o Arg` is separate form.
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`--option=Arg` is stuck, `--option Arg` is separate form.
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* Long options may be 'abbreviated', as long as the abbreviation
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is unambiguous.
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* Short options may be bundled, e.g. `-a -b` can be specified as `-ab`.
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* Boolean long options can be 'negated' (or 'unset') by prepending
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`no-`, e.g. `--no-abbrev` instead of `--abbrev`. Conversely,
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options that begin with `no-` can be 'negated' by removing it.
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Other long options can be unset (e.g., set string to NULL, set
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integer to 0) by prepending `no-`.
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* Options and non-option arguments can clearly be separated using the `--`
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option, e.g. `-a -b --option -- --this-is-a-file` indicates that
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`--this-is-a-file` must not be processed as an option.
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Steps to parse options
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----------------------
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. `#include "parse-options.h"`
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. define a NULL-terminated
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`static const char * const builtin_foo_usage[]` array
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containing alternative usage strings
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. define `builtin_foo_options` array as described below
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in section 'Data Structure'.
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. in `cmd_foo(int argc, const char **argv, const char *prefix)`
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call
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argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags);
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+
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`parse_options()` will filter out the processed options of `argv[]` and leave the
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non-option arguments in `argv[]`.
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`argc` is updated appropriately because of the assignment.
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+
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You can also pass NULL instead of a usage array as the fifth parameter of
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parse_options(), to avoid displaying a help screen with usage info and
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option list. This should only be done if necessary, e.g. to implement
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a limited parser for only a subset of the options that needs to be run
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before the full parser, which in turn shows the full help message.
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+
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Flags are the bitwise-or of:
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`PARSE_OPT_KEEP_DASHDASH`::
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Keep the `--` that usually separates options from
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non-option arguments.
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`PARSE_OPT_STOP_AT_NON_OPTION`::
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Usually the whole argument vector is massaged and reordered.
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Using this flag, processing is stopped at the first non-option
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argument.
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`PARSE_OPT_KEEP_ARGV0`::
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Keep the first argument, which contains the program name. It's
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removed from argv[] by default.
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`PARSE_OPT_KEEP_UNKNOWN`::
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Keep unknown arguments instead of erroring out. This doesn't
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work for all combinations of arguments as users might expect
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it to do. E.g. if the first argument in `--unknown --known`
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takes a value (which we can't know), the second one is
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mistakenly interpreted as a known option. Similarly, if
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`PARSE_OPT_STOP_AT_NON_OPTION` is set, the second argument in
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`--unknown value` will be mistakenly interpreted as a
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non-option, not as a value belonging to the unknown option,
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the parser early. That's why parse_options() errors out if
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both options are set.
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`PARSE_OPT_NO_INTERNAL_HELP`::
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By default, parse_options() handles `-h`, `--help` and
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`--help-all` internally, by showing a help screen. This option
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turns it off and allows one to add custom handlers for these
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options, or to just leave them unknown.
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Data Structure
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--------------
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The main data structure is an array of the `option` struct,
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say `static struct option builtin_add_options[]`.
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There are some macros to easily define options:
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`OPT__ABBREV(&int_var)`::
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Add `--abbrev[=<n>]`.
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`OPT__COLOR(&int_var, description)`::
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Add `--color[=<when>]` and `--no-color`.
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`OPT__DRY_RUN(&int_var, description)`::
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Add `-n, --dry-run`.
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`OPT__FORCE(&int_var, description)`::
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Add `-f, --force`.
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`OPT__QUIET(&int_var, description)`::
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Add `-q, --quiet`.
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`OPT__VERBOSE(&int_var, description)`::
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Add `-v, --verbose`.
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`OPT_GROUP(description)`::
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Start an option group. `description` is a short string that
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describes the group or an empty string.
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Start the description with an upper-case letter.
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`OPT_BOOL(short, long, &int_var, description)`::
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Introduce a boolean option. `int_var` is set to one with
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`--option` and set to zero with `--no-option`.
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`OPT_COUNTUP(short, long, &int_var, description)`::
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Introduce a count-up option.
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`int_var` is incremented on each use of `--option`, and
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reset to zero with `--no-option`.
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`OPT_BIT(short, long, &int_var, description, mask)`::
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Introduce a boolean option.
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If used, `int_var` is bitwise-ored with `mask`.
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`OPT_NEGBIT(short, long, &int_var, description, mask)`::
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Introduce a boolean option.
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If used, `int_var` is bitwise-anded with the inverted `mask`.
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`OPT_SET_INT(short, long, &int_var, description, integer)`::
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Introduce an integer option.
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`int_var` is set to `integer` with `--option`, and
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reset to zero with `--no-option`.
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`OPT_STRING(short, long, &str_var, arg_str, description)`::
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Introduce an option with string argument.
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The string argument is put into `str_var`.
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`OPT_INTEGER(short, long, &int_var, description)`::
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Introduce an option with integer argument.
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The integer is put into `int_var`.
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`OPT_DATE(short, long, &int_var, description)`::
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Introduce an option with date argument, see `approxidate()`.
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The timestamp is put into `int_var`.
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`OPT_EXPIRY_DATE(short, long, &int_var, description)`::
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Introduce an option with expiry date argument, see `parse_expiry_date()`.
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The timestamp is put into `int_var`.
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`OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`::
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Introduce an option with argument.
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The argument will be fed into the function given by `func_ptr`
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and the result will be put into `var`.
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See 'Option Callbacks' below for a more elaborate description.
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`OPT_FILENAME(short, long, &var, description)`::
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Introduce an option with a filename argument.
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The filename will be prefixed by passing the filename along with
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the prefix argument of `parse_options()` to `prefix_filename()`.
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`OPT_ARGUMENT(long, description)`::
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Introduce a long-option argument that will be kept in `argv[]`.
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`OPT_NUMBER_CALLBACK(&var, description, func_ptr)`::
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Recognize numerical options like -123 and feed the integer as
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if it was an argument to the function given by `func_ptr`.
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The result will be put into `var`. There can be only one such
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option definition. It cannot be negated and it takes no
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arguments. Short options that happen to be digits take
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precedence over it.
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`OPT_COLOR_FLAG(short, long, &int_var, description)`::
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Introduce an option that takes an optional argument that can
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have one of three values: "always", "never", or "auto". If the
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argument is not given, it defaults to "always". The `--no-` form
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works like `--long=never`; it cannot take an argument. If
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"always", set `int_var` to 1; if "never", set `int_var` to 0; if
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"auto", set `int_var` to 1 if stdout is a tty or a pager,
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0 otherwise.
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`OPT_NOOP_NOARG(short, long)`::
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Introduce an option that has no effect and takes no arguments.
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Use it to hide deprecated options that are still to be recognized
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and ignored silently.
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The last element of the array must be `OPT_END()`.
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If not stated otherwise, interpret the arguments as follows:
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* `short` is a character for the short option
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(e.g. `'e'` for `-e`, use `0` to omit),
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* `long` is a string for the long option
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(e.g. `"example"` for `--example`, use `NULL` to omit),
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* `int_var` is an integer variable,
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* `str_var` is a string variable (`char *`),
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* `arg_str` is the string that is shown as argument
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(e.g. `"branch"` will result in `<branch>`).
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If set to `NULL`, three dots (`...`) will be displayed.
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* `description` is a short string to describe the effect of the option.
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It shall begin with a lower-case letter and a full stop (`.`) shall be
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omitted at the end.
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Option Callbacks
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----------------
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The function must be defined in this form:
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int func(const struct option *opt, const char *arg, int unset)
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The callback mechanism is as follows:
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* Inside `func`, the only interesting member of the structure
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given by `opt` is the void pointer `opt->value`.
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`*opt->value` will be the value that is saved into `var`, if you
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use `OPT_CALLBACK()`.
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For example, do `*(unsigned long *)opt->value = 42;` to get 42
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into an `unsigned long` variable.
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* Return value `0` indicates success and non-zero return
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value will invoke `usage_with_options()` and, thus, die.
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* If the user negates the option, `arg` is `NULL` and `unset` is 1.
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Sophisticated option parsing
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----------------------------
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If you need, for example, option callbacks with optional arguments
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or without arguments at all, or if you need other special cases,
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that are not handled by the macros above, you need to specify the
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members of the `option` structure manually.
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This is not covered in this document, but well documented
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in `parse-options.h` itself.
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Examples
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--------
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See `test-parse-options.c` and
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`builtin/add.c`,
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`builtin/clone.c`,
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`builtin/commit.c`,
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`builtin/fetch.c`,
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`builtin/fsck.c`,
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`builtin/rm.c`
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for real-world examples.
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