parseopt: add OPT_NEGBIT
[git/git.git] / Documentation / technical / api-parse-options.txt
1 parse-options API
2 =================
3
4 The parse-options API is used to parse and massage options in git
5 and to provide a usage help with consistent look.
6
7 Basics
8 ------
9
10 The argument vector `argv[]` may usually contain mandatory or optional
11 'non-option arguments', e.g. a filename or a branch, and 'options'.
12 Options are optional arguments that start with a dash and
13 that 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
30 The 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
48 Steps 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
63 argc = parse_options(argc, argv, builtin_foo_options, builtin_foo_usage, flags);
64 +
65 `parse_options()` will filter out the processed options of `argv[]` and leave the
66 non-option arguments in `argv[]`.
67 `argc` is updated appropriately because of the assignment.
68 +
69 You can also pass NULL instead of a usage array as fourth parameter of
70 parse_options(), to avoid displaying a help screen with usage info and
71 option list. This should only be done if necessary, e.g. to implement
72 a limited parser for only a subset of the options that needs to be run
73 before the full parser, which in turn shows the full help message.
74 +
75 Flags 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
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,
99 the parser early. That's why parse_options() errors out if
100 both options are set.
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
108 Data Structure
109 --------------
110
111 The main data structure is an array of the `option` struct,
112 say `static struct option builtin_add_options[]`.
113 There are some macros to easily define options:
114
115 `OPT__ABBREV(&int_var)`::
116 Add `\--abbrev[=<n>]`.
117
118 `OPT__DRY_RUN(&int_var)`::
119 Add `-n, \--dry-run`.
120
121 `OPT__QUIET(&int_var)`::
122 Add `-q, \--quiet`.
123
124 `OPT__VERBOSE(&int_var)`::
125 Add `-v, \--verbose`.
126
127 `OPT_GROUP(description)`::
128 Start an option group. `description` is a short string that
129 describes the group or an empty string.
130 Start the description with an upper-case letter.
131
132 `OPT_BOOLEAN(short, long, &int_var, description)`::
133 Introduce a boolean option.
134 `int_var` is incremented on each use.
135
136 `OPT_BIT(short, long, &int_var, description, mask)`::
137 Introduce a boolean option.
138 If used, `int_var` is bitwise-ored with `mask`.
139
140 `OPT_NEGBIT(short, long, &int_var, description, mask)`::
141 Introduce a boolean option.
142 If used, `int_var` is bitwise-anded with the inverted `mask`.
143
144 `OPT_SET_INT(short, long, &int_var, description, integer)`::
145 Introduce a boolean option.
146 If used, set `int_var` to `integer`.
147
148 `OPT_SET_PTR(short, long, &ptr_var, description, ptr)`::
149 Introduce a boolean option.
150 If used, set `ptr_var` to `ptr`.
151
152 `OPT_STRING(short, long, &str_var, arg_str, description)`::
153 Introduce an option with string argument.
154 The string argument is put into `str_var`.
155
156 `OPT_INTEGER(short, long, &int_var, description)`::
157 Introduce an option with integer argument.
158 The integer is put into `int_var`.
159
160 `OPT_DATE(short, long, &int_var, description)`::
161 Introduce an option with date argument, see `approxidate()`.
162 The timestamp is put into `int_var`.
163
164 `OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`::
165 Introduce an option with argument.
166 The argument will be fed into the function given by `func_ptr`
167 and the result will be put into `var`.
168 See 'Option Callbacks' below for a more elaborate description.
169
170 `OPT_ARGUMENT(long, description)`::
171 Introduce a long-option argument that will be kept in `argv[]`.
172
173
174 The last element of the array must be `OPT_END()`.
175
176 If not stated otherwise, interpret the arguments as follows:
177
178 * `short` is a character for the short option
179 (e.g. `\'e\'` for `-e`, use `0` to omit),
180
181 * `long` is a string for the long option
182 (e.g. `"example"` for `\--example`, use `NULL` to omit),
183
184 * `int_var` is an integer variable,
185
186 * `str_var` is a string variable (`char *`),
187
188 * `arg_str` is the string that is shown as argument
189 (e.g. `"branch"` will result in `<branch>`).
190 If set to `NULL`, three dots (`...`) will be displayed.
191
192 * `description` is a short string to describe the effect of the option.
193 It shall begin with a lower-case letter and a full stop (`.`) shall be
194 omitted at the end.
195
196 Option Callbacks
197 ----------------
198
199 The function must be defined in this form:
200
201 int func(const struct option *opt, const char *arg, int unset)
202
203 The callback mechanism is as follows:
204
205 * Inside `funct`, the only interesting member of the structure
206 given by `opt` is the void pointer `opt->value`.
207 `\*opt->value` will be the value that is saved into `var`, if you
208 use `OPT_CALLBACK()`.
209 For example, do `*(unsigned long *)opt->value = 42;` to get 42
210 into an `unsigned long` variable.
211
212 * Return value `0` indicates success and non-zero return
213 value will invoke `usage_with_options()` and, thus, die.
214
215 * If the user negates the option, `arg` is `NULL` and `unset` is 1.
216
217 Sophisticated option parsing
218 ----------------------------
219
220 If you need, for example, option callbacks with optional arguments
221 or without arguments at all, or if you need other special cases,
222 that are not handled by the macros above, you need to specify the
223 members of the `option` structure manually.
224
225 This is not covered in this document, but well documented
226 in `parse-options.h` itself.
227
228 Examples
229 --------
230
231 See `test-parse-options.c` and
232 `builtin-add.c`,
233 `builtin-clone.c`,
234 `builtin-commit.c`,
235 `builtin-fetch.c`,
236 `builtin-fsck.c`,
237 `builtin-rm.c`
238 for real-world examples.