add description parameter to OPT__QUIET
[git/git.git] / Documentation / technical / api-parse-options.txt
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1parse-options API
2=================
3
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4The parse-options API is used to parse and massage options in git
5and to provide a usage help with consistent look.
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7Basics
8------
9
10The argument vector `argv[]` may usually contain mandatory or optional
11'non-option arguments', e.g. a filename or a branch, and 'options'.
12Options are optional arguments that start with a dash and
13that allow to change the behavior of a command.
14
15* There are basically three types of options:
16 'boolean' options,
17 options with (mandatory) 'arguments' and
18 options with 'optional arguments'
19 (i.e. a boolean option that can be adjusted).
20
21* There are basically two forms of options:
22 'Short options' consist of one dash (`-`) and one alphanumeric
23 character.
24 'Long options' begin with two dashes (`\--`) and some
25 alphanumeric characters.
26
27* Options are case-sensitive.
28 Please define 'lower-case long options' only.
29
30The parse-options API allows:
31
32* 'sticked' and 'separate form' of options with arguments.
33 `-oArg` is sticked, `-o Arg` is separate form.
34 `\--option=Arg` is sticked, `\--option Arg` is separate form.
35
36* Long options may be 'abbreviated', as long as the abbreviation
37 is unambiguous.
38
39* Short options may be bundled, e.g. `-a -b` can be specified as `-ab`.
40
41* Boolean long options can be 'negated' (or 'unset') by prepending
42 `no-`, e.g. `\--no-abbrev` instead of `\--abbrev`.
43
44* Options and non-option arguments can clearly be separated using the `\--`
45 option, e.g. `-a -b \--option \-- \--this-is-a-file` indicates that
46 `\--this-is-a-file` must not be processed as an option.
47
48Steps to parse options
49----------------------
50
51. `#include "parse-options.h"`
52
53. define a NULL-terminated
54 `static const char * const builtin_foo_usage[]` array
55 containing alternative usage strings
56
57. define `builtin_foo_options` array as described below
58 in section 'Data Structure'.
59
60. in `cmd_foo(int argc, const char **argv, const char *prefix)`
61 call
62
37782920 63 argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags);
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64+
65`parse_options()` will filter out the processed options of `argv[]` and leave the
66non-option arguments in `argv[]`.
67`argc` is updated appropriately because of the assignment.
68+
37782920 69You can also pass NULL instead of a usage array as the fifth parameter of
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70parse_options(), to avoid displaying a help screen with usage info and
71option list. This should only be done if necessary, e.g. to implement
72a limited parser for only a subset of the options that needs to be run
73before the full parser, which in turn shows the full help message.
74+
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75Flags are the bitwise-or of:
76
77`PARSE_OPT_KEEP_DASHDASH`::
78 Keep the `\--` that usually separates options from
79 non-option arguments.
80
81`PARSE_OPT_STOP_AT_NON_OPTION`::
82 Usually the whole argument vector is massaged and reordered.
83 Using this flag, processing is stopped at the first non-option
84 argument.
85
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86`PARSE_OPT_KEEP_ARGV0`::
87 Keep the first argument, which contains the program name. It's
88 removed from argv[] by default.
89
90`PARSE_OPT_KEEP_UNKNOWN`::
91 Keep unknown arguments instead of erroring out. This doesn't
92 work for all combinations of arguments as users might expect
93 it to do. E.g. if the first argument in `--unknown --known`
94 takes a value (which we can't know), the second one is
95 mistakenly interpreted as a known option. Similarly, if
96 `PARSE_OPT_STOP_AT_NON_OPTION` is set, the second argument in
97 `--unknown value` will be mistakenly interpreted as a
98 non-option, not as a value belonging to the unknown option,
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99 the parser early. That's why parse_options() errors out if
100 both options are set.
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101
102`PARSE_OPT_NO_INTERNAL_HELP`::
103 By default, parse_options() handles `-h`, `--help` and
104 `--help-all` internally, by showing a help screen. This option
105 turns it off and allows one to add custom handlers for these
106 options, or to just leave them unknown.
107
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108Data Structure
109--------------
110
111The main data structure is an array of the `option` struct,
112say `static struct option builtin_add_options[]`.
113There are some macros to easily define options:
114
115`OPT__ABBREV(&int_var)`::
116 Add `\--abbrev[=<n>]`.
117
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118`OPT__COLOR(&int_var, description)`::
119 Add `\--color[=<when>]` and `--no-color`.
120
e21adb8c 121`OPT__DRY_RUN(&int_var, description)`::
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122 Add `-n, \--dry-run`.
123
d52ee6e6 124`OPT__QUIET(&int_var, description)`::
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125 Add `-q, \--quiet`.
126
fd03881a 127`OPT__VERBOSE(&int_var, description)`::
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128 Add `-v, \--verbose`.
129
130`OPT_GROUP(description)`::
131 Start an option group. `description` is a short string that
132 describes the group or an empty string.
133 Start the description with an upper-case letter.
134
135`OPT_BOOLEAN(short, long, &int_var, description)`::
136 Introduce a boolean option.
137 `int_var` is incremented on each use.
138
139`OPT_BIT(short, long, &int_var, description, mask)`::
140 Introduce a boolean option.
141 If used, `int_var` is bitwise-ored with `mask`.
142
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143`OPT_NEGBIT(short, long, &int_var, description, mask)`::
144 Introduce a boolean option.
145 If used, `int_var` is bitwise-anded with the inverted `mask`.
146
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147`OPT_SET_INT(short, long, &int_var, description, integer)`::
148 Introduce a boolean option.
149 If used, set `int_var` to `integer`.
150
151`OPT_SET_PTR(short, long, &ptr_var, description, ptr)`::
152 Introduce a boolean option.
153 If used, set `ptr_var` to `ptr`.
154
155`OPT_STRING(short, long, &str_var, arg_str, description)`::
156 Introduce an option with string argument.
157 The string argument is put into `str_var`.
158
159`OPT_INTEGER(short, long, &int_var, description)`::
160 Introduce an option with integer argument.
161 The integer is put into `int_var`.
162
163`OPT_DATE(short, long, &int_var, description)`::
164 Introduce an option with date argument, see `approxidate()`.
165 The timestamp is put into `int_var`.
166
167`OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`::
168 Introduce an option with argument.
169 The argument will be fed into the function given by `func_ptr`
170 and the result will be put into `var`.
171 See 'Option Callbacks' below for a more elaborate description.
172
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173`OPT_FILENAME(short, long, &var, description)`::
174 Introduce an option with a filename argument.
175 The filename will be prefixed by passing the filename along with
176 the prefix argument of `parse_options()` to `prefix_filename()`.
177
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178`OPT_ARGUMENT(long, description)`::
179 Introduce a long-option argument that will be kept in `argv[]`.
180
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181`OPT_NUMBER_CALLBACK(&var, description, func_ptr)`::
182 Recognize numerical options like -123 and feed the integer as
183 if it was an argument to the function given by `func_ptr`.
184 The result will be put into `var`. There can be only one such
185 option definition. It cannot be negated and it takes no
186 arguments. Short options that happen to be digits take
187 precedence over it.
188
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189`OPT_COLOR_FLAG(short, long, &int_var, description)`::
190 Introduce an option that takes an optional argument that can
191 have one of three values: "always", "never", or "auto". If the
192 argument is not given, it defaults to "always". The `--no-` form
193 works like `--long=never`; it cannot take an argument. If
194 "always", set `int_var` to 1; if "never", set `int_var` to 0; if
195 "auto", set `int_var` to 1 if stdout is a tty or a pager,
196 0 otherwise.
197
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198
199The last element of the array must be `OPT_END()`.
200
201If not stated otherwise, interpret the arguments as follows:
202
203* `short` is a character for the short option
6dcca4d0 204 (e.g. `{apostrophe}e{apostrophe}` for `-e`, use `0` to omit),
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205
206* `long` is a string for the long option
207 (e.g. `"example"` for `\--example`, use `NULL` to omit),
208
209* `int_var` is an integer variable,
210
211* `str_var` is a string variable (`char *`),
212
213* `arg_str` is the string that is shown as argument
214 (e.g. `"branch"` will result in `<branch>`).
215 If set to `NULL`, three dots (`...`) will be displayed.
216
217* `description` is a short string to describe the effect of the option.
218 It shall begin with a lower-case letter and a full stop (`.`) shall be
219 omitted at the end.
220
221Option Callbacks
222----------------
223
224The function must be defined in this form:
225
226 int func(const struct option *opt, const char *arg, int unset)
227
228The callback mechanism is as follows:
229
ca156cfc 230* Inside `func`, the only interesting member of the structure
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231 given by `opt` is the void pointer `opt\->value`.
232 `\*opt\->value` will be the value that is saved into `var`, if you
224712e5 233 use `OPT_CALLBACK()`.
6dcca4d0 234 For example, do `*(unsigned long *)opt\->value = 42;` to get 42
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235 into an `unsigned long` variable.
236
237* Return value `0` indicates success and non-zero return
238 value will invoke `usage_with_options()` and, thus, die.
239
240* If the user negates the option, `arg` is `NULL` and `unset` is 1.
241
242Sophisticated option parsing
243----------------------------
244
245If you need, for example, option callbacks with optional arguments
246or without arguments at all, or if you need other special cases,
247that are not handled by the macros above, you need to specify the
248members of the `option` structure manually.
249
250This is not covered in this document, but well documented
251in `parse-options.h` itself.
252
253Examples
254--------
255
256See `test-parse-options.c` and
257`builtin-add.c`,
258`builtin-clone.c`,
259`builtin-commit.c`,
260`builtin-fetch.c`,
261`builtin-fsck.c`,
262`builtin-rm.c`
263for real-world examples.