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