1parse-options API 2================= 3 4The parse-options API is used to parse and massage options in Git 5and to provide a usage help with consistent look. 6 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* 'stuck' and 'separate form' of options with arguments. 33 `-oArg` is stuck, `-o Arg` is separate form. 34 `--option=Arg` is stuck, `--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`. Conversely, 43 options that begin with `no-` can be 'negated' by removing it. 44 Other long options can be unset (e.g., set string to NULL, set 45 integer to 0) by prepending `no-`. 46 47* Options and non-option arguments can clearly be separated using the `--` 48 option, e.g. `-a -b --option -- --this-is-a-file` indicates that 49 `--this-is-a-file` must not be processed as an option. 50 51Steps to parse options 52---------------------- 53 54. `#include "parse-options.h"` 55 56. define a NULL-terminated 57 `static const char * const builtin_foo_usage[]` array 58 containing alternative usage strings 59 60. define `builtin_foo_options` array as described below 61 in section 'Data Structure'. 62 63. in `cmd_foo(int argc, const char **argv, const char *prefix)` 64 call 65 66 argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags); 67+ 68`parse_options()` will filter out the processed options of `argv[]` and leave the 69non-option arguments in `argv[]`. 70`argc` is updated appropriately because of the assignment. 71+ 72You can also pass NULL instead of a usage array as the fifth parameter of 73parse_options(), to avoid displaying a help screen with usage info and 74option list. This should only be done if necessary, e.g. to implement 75a limited parser for only a subset of the options that needs to be run 76before the full parser, which in turn shows the full help message. 77+ 78Flags are the bitwise-or of: 79 80`PARSE_OPT_KEEP_DASHDASH`:: 81 Keep the `--` that usually separates options from 82 non-option arguments. 83 84`PARSE_OPT_STOP_AT_NON_OPTION`:: 85 Usually the whole argument vector is massaged and reordered. 86 Using this flag, processing is stopped at the first non-option 87 argument. 88 89`PARSE_OPT_KEEP_ARGV0`:: 90 Keep the first argument, which contains the program name. It's 91 removed from argv[] by default. 92 93`PARSE_OPT_KEEP_UNKNOWN`:: 94 Keep unknown arguments instead of erroring out. This doesn't 95 work for all combinations of arguments as users might expect 96 it to do. E.g. if the first argument in `--unknown --known` 97 takes a value (which we can't know), the second one is 98 mistakenly interpreted as a known option. Similarly, if 99 `PARSE_OPT_STOP_AT_NON_OPTION` is set, the second argument in 100 `--unknown value` will be mistakenly interpreted as a 101 non-option, not as a value belonging to the unknown option, 102 the parser early. That's why parse_options() errors out if 103 both options are set. 104 105`PARSE_OPT_NO_INTERNAL_HELP`:: 106 By default, parse_options() handles `-h`, `--help` and 107 `--help-all` internally, by showing a help screen. This option 108 turns it off and allows one to add custom handlers for these 109 options, or to just leave them unknown. 110 111Data Structure 112-------------- 113 114The main data structure is an array of the `option` struct, 115say `static struct option builtin_add_options[]`. 116There are some macros to easily define options: 117 118`OPT__ABBREV(&int_var)`:: 119 Add `--abbrev[=<n>]`. 120 121`OPT__COLOR(&int_var, description)`:: 122 Add `--color[=<when>]` and `--no-color`. 123 124`OPT__DRY_RUN(&int_var, description)`:: 125 Add `-n, --dry-run`. 126 127`OPT__FORCE(&int_var, description)`:: 128 Add `-f, --force`. 129 130`OPT__QUIET(&int_var, description)`:: 131 Add `-q, --quiet`. 132 133`OPT__VERBOSE(&int_var, description)`:: 134 Add `-v, --verbose`. 135 136`OPT_GROUP(description)`:: 137 Start an option group. `description` is a short string that 138 describes the group or an empty string. 139 Start the description with an upper-case letter. 140 141`OPT_BOOL(short, long, &int_var, description)`:: 142 Introduce a boolean option. `int_var` is set to one with 143 `--option` and set to zero with `--no-option`. 144 145`OPT_COUNTUP(short, long, &int_var, description)`:: 146 Introduce a count-up option. 147 `int_var` is incremented on each use of `--option`, and 148 reset to zero with `--no-option`. 149 150`OPT_BIT(short, long, &int_var, description, mask)`:: 151 Introduce a boolean option. 152 If used, `int_var` is bitwise-ored with `mask`. 153 154`OPT_NEGBIT(short, long, &int_var, description, mask)`:: 155 Introduce a boolean option. 156 If used, `int_var` is bitwise-anded with the inverted `mask`. 157 158`OPT_SET_INT(short, long, &int_var, description, integer)`:: 159 Introduce an integer option. 160 `int_var` is set to `integer` with `--option`, and 161 reset to zero with `--no-option`. 162 163`OPT_STRING(short, long, &str_var, arg_str, description)`:: 164 Introduce an option with string argument. 165 The string argument is put into `str_var`. 166 167`OPT_INTEGER(short, long, &int_var, description)`:: 168 Introduce an option with integer argument. 169 The integer is put into `int_var`. 170 171`OPT_MAGNITUDE(short, long, &unsigned_long_var, description)`:: 172 Introduce an option with a size argument. The argument must be a 173 non-negative integer and may include a suffix of 'k', 'm' or 'g' to 174 scale the provided value by 1024, 1024^2 or 1024^3 respectively. 175 The scaled value is put into `unsigned_long_var`. 176 177`OPT_DATE(short, long, &int_var, description)`:: 178 Introduce an option with date argument, see `approxidate()`. 179 The timestamp is put into `int_var`. 180 181`OPT_EXPIRY_DATE(short, long, &int_var, description)`:: 182 Introduce an option with expiry date argument, see `parse_expiry_date()`. 183 The timestamp is put into `int_var`. 184 185`OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`:: 186 Introduce an option with argument. 187 The argument will be fed into the function given by `func_ptr` 188 and the result will be put into `var`. 189 See 'Option Callbacks' below for a more elaborate description. 190 191`OPT_FILENAME(short, long, &var, description)`:: 192 Introduce an option with a filename argument. 193 The filename will be prefixed by passing the filename along with 194 the prefix argument of `parse_options()` to `prefix_filename()`. 195 196`OPT_ARGUMENT(long, description)`:: 197 Introduce a long-option argument that will be kept in `argv[]`. 198 199`OPT_NUMBER_CALLBACK(&var, description, func_ptr)`:: 200 Recognize numerical options like -123 and feed the integer as 201 if it was an argument to the function given by `func_ptr`. 202 The result will be put into `var`. There can be only one such 203 option definition. It cannot be negated and it takes no 204 arguments. Short options that happen to be digits take 205 precedence over it. 206 207`OPT_COLOR_FLAG(short, long, &int_var, description)`:: 208 Introduce an option that takes an optional argument that can 209 have one of three values: "always", "never", or "auto". If the 210 argument is not given, it defaults to "always". The `--no-` form 211 works like `--long=never`; it cannot take an argument. If 212 "always", set `int_var` to 1; if "never", set `int_var` to 0; if 213 "auto", set `int_var` to 1 if stdout is a tty or a pager, 214 0 otherwise. 215 216`OPT_NOOP_NOARG(short, long)`:: 217 Introduce an option that has no effect and takes no arguments. 218 Use it to hide deprecated options that are still to be recognized 219 and ignored silently. 220 221`OPT_PASSTHRU(short, long, &char_var, arg_str, description, flags)`:: 222 Introduce an option that will be reconstructed into a char* string, 223 which must be initialized to NULL. This is useful when you need to 224 pass the command-line option to another command. Any previous value 225 will be overwritten, so this should only be used for options where 226 the last one specified on the command line wins. 227 228`OPT_PASSTHRU_ARGV(short, long, &argv_array_var, arg_str, description, flags)`:: 229 Introduce an option where all instances of it on the command-line will 230 be reconstructed into an argv_array. This is useful when you need to 231 pass the command-line option, which can be specified multiple times, 232 to another command. 233 234 235The last element of the array must be `OPT_END()`. 236 237If not stated otherwise, interpret the arguments as follows: 238 239* `short` is a character for the short option 240 (e.g. `'e'` for `-e`, use `0` to omit), 241 242* `long` is a string for the long option 243 (e.g. `"example"` for `--example`, use `NULL` to omit), 244 245* `int_var` is an integer variable, 246 247* `str_var` is a string variable (`char *`), 248 249* `arg_str` is the string that is shown as argument 250 (e.g. `"branch"` will result in `<branch>`). 251 If set to `NULL`, three dots (`...`) will be displayed. 252 253* `description` is a short string to describe the effect of the option. 254 It shall begin with a lower-case letter and a full stop (`.`) shall be 255 omitted at the end. 256 257Option Callbacks 258---------------- 259 260The function must be defined in this form: 261 262 int func(const struct option *opt, const char *arg, int unset) 263 264The callback mechanism is as follows: 265 266* Inside `func`, the only interesting member of the structure 267 given by `opt` is the void pointer `opt->value`. 268 `*opt->value` will be the value that is saved into `var`, if you 269 use `OPT_CALLBACK()`. 270 For example, do `*(unsigned long *)opt->value = 42;` to get 42 271 into an `unsigned long` variable. 272 273* Return value `0` indicates success and non-zero return 274 value will invoke `usage_with_options()` and, thus, die. 275 276* If the user negates the option, `arg` is `NULL` and `unset` is 1. 277 278Sophisticated option parsing 279---------------------------- 280 281If you need, for example, option callbacks with optional arguments 282or without arguments at all, or if you need other special cases, 283that are not handled by the macros above, you need to specify the 284members of the `option` structure manually. 285 286This is not covered in this document, but well documented 287in `parse-options.h` itself. 288 289Examples 290-------- 291 292See `test-parse-options.c` and 293`builtin/add.c`, 294`builtin/clone.c`, 295`builtin/commit.c`, 296`builtin/fetch.c`, 297`builtin/fsck.c`, 298`builtin/rm.c` 299for real-world examples.