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* '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 63 argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags); 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+ 69You can also pass NULL instead of a usage array as the fifth parameter of 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+ 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 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 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>]`. 117 118`OPT__COLOR(&int_var, description)`:: 119 Add `\--color[=<when>]` and `--no-color`. 120 121`OPT__DRY_RUN(&int_var, description)`:: 122 Add `-n, \--dry-run`. 123 124`OPT__FORCE(&int_var, description)`:: 125 Add `-f, \--force`. 126 127`OPT__QUIET(&int_var, description)`:: 128 Add `-q, \--quiet`. 129 130`OPT__VERBOSE(&int_var, description)`:: 131 Add `-v, \--verbose`. 132 133`OPT_GROUP(description)`:: 134 Start an option group. `description` is a short string that 135 describes the group or an empty string. 136 Start the description with an upper-case letter. 137 138`OPT_BOOLEAN(short, long, &int_var, description)`:: 139 Introduce a boolean option. 140 `int_var` is incremented on each use. 141 142`OPT_BIT(short, long, &int_var, description, mask)`:: 143 Introduce a boolean option. 144 If used, `int_var` is bitwise-ored with `mask`. 145 146`OPT_NEGBIT(short, long, &int_var, description, mask)`:: 147 Introduce a boolean option. 148 If used, `int_var` is bitwise-anded with the inverted `mask`. 149 150`OPT_SET_INT(short, long, &int_var, description, integer)`:: 151 Introduce a boolean option. 152 If used, set `int_var` to `integer`. 153 154`OPT_SET_PTR(short, long, &ptr_var, description, ptr)`:: 155 Introduce a boolean option. 156 If used, set `ptr_var` to `ptr`. 157 158`OPT_STRING(short, long, &str_var, arg_str, description)`:: 159 Introduce an option with string argument. 160 The string argument is put into `str_var`. 161 162`OPT_INTEGER(short, long, &int_var, description)`:: 163 Introduce an option with integer argument. 164 The integer is put into `int_var`. 165 166`OPT_DATE(short, long, &int_var, description)`:: 167 Introduce an option with date argument, see `approxidate()`. 168 The timestamp is put into `int_var`. 169 170`OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`:: 171 Introduce an option with argument. 172 The argument will be fed into the function given by `func_ptr` 173 and the result will be put into `var`. 174 See 'Option Callbacks' below for a more elaborate description. 175 176`OPT_FILENAME(short, long, &var, description)`:: 177 Introduce an option with a filename argument. 178 The filename will be prefixed by passing the filename along with 179 the prefix argument of `parse_options()` to `prefix_filename()`. 180 181`OPT_ARGUMENT(long, description)`:: 182 Introduce a long-option argument that will be kept in `argv[]`. 183 184`OPT_NUMBER_CALLBACK(&var, description, func_ptr)`:: 185 Recognize numerical options like -123 and feed the integer as 186 if it was an argument to the function given by `func_ptr`. 187 The result will be put into `var`. There can be only one such 188 option definition. It cannot be negated and it takes no 189 arguments. Short options that happen to be digits take 190 precedence over it. 191 192`OPT_COLOR_FLAG(short, long, &int_var, description)`:: 193 Introduce an option that takes an optional argument that can 194 have one of three values: "always", "never", or "auto". If the 195 argument is not given, it defaults to "always". The `--no-` form 196 works like `--long=never`; it cannot take an argument. If 197 "always", set `int_var` to 1; if "never", set `int_var` to 0; if 198 "auto", set `int_var` to 1 if stdout is a tty or a pager, 199 0 otherwise. 200 201 202The last element of the array must be `OPT_END()`. 203 204If not stated otherwise, interpret the arguments as follows: 205 206* `short` is a character for the short option 207 (e.g. `{apostrophe}e{apostrophe}` for `-e`, use `0` to omit), 208 209* `long` is a string for the long option 210 (e.g. `"example"` for `\--example`, use `NULL` to omit), 211 212* `int_var` is an integer variable, 213 214* `str_var` is a string variable (`char *`), 215 216* `arg_str` is the string that is shown as argument 217 (e.g. `"branch"` will result in `<branch>`). 218 If set to `NULL`, three dots (`...`) will be displayed. 219 220* `description` is a short string to describe the effect of the option. 221 It shall begin with a lower-case letter and a full stop (`.`) shall be 222 omitted at the end. 223 224Option Callbacks 225---------------- 226 227The function must be defined in this form: 228 229 int func(const struct option *opt, const char *arg, int unset) 230 231The callback mechanism is as follows: 232 233* Inside `func`, the only interesting member of the structure 234 given by `opt` is the void pointer `opt\->value`. 235 `\*opt\->value` will be the value that is saved into `var`, if you 236 use `OPT_CALLBACK()`. 237 For example, do `*(unsigned long *)opt\->value = 42;` to get 42 238 into an `unsigned long` variable. 239 240* Return value `0` indicates success and non-zero return 241 value will invoke `usage_with_options()` and, thus, die. 242 243* If the user negates the option, `arg` is `NULL` and `unset` is 1. 244 245Sophisticated option parsing 246---------------------------- 247 248If you need, for example, option callbacks with optional arguments 249or without arguments at all, or if you need other special cases, 250that are not handled by the macros above, you need to specify the 251members of the `option` structure manually. 252 253This is not covered in this document, but well documented 254in `parse-options.h` itself. 255 256Examples 257-------- 258 259See `test-parse-options.c` and 260`builtin-add.c`, 261`builtin-clone.c`, 262`builtin-commit.c`, 263`builtin-fetch.c`, 264`builtin-fsck.c`, 265`builtin-rm.c` 266for real-world examples.