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)`:: 122 Add `-n, \--dry-run`. 123 124`OPT__QUIET(&int_var)`:: 125 Add `-q, \--quiet`. 126 127`OPT__VERBOSE(&int_var)`:: 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`. 142 143`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`. 146 147`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. 172 173`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()`. 177 178`OPT_ARGUMENT(long, description)`:: 179 Introduce a long-option argument that will be kept in `argv[]`. 180 181`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. 188 189`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. 197 198 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 204 (e.g. `\'e\'` for `-e`, use `0` to omit), 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: 229 230* Inside `func`, the only interesting member of the structure 231 given by `opt` is the void pointer `opt->value`. 232 `\*opt->value` will be the value that is saved into `var`, if you 233 use `OPT_CALLBACK()`. 234 For example, do `*(unsigned long *)opt->value = 42;` to get 42 235 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.