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, 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 fourth 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__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_SET_INT(short, long, &int_var, description, integer)`:: 141 Introduce a boolean option. 142 If used, set `int_var` to `integer`. 143 144`OPT_SET_PTR(short, long, &ptr_var, description, ptr)`:: 145 Introduce a boolean option. 146 If used, set `ptr_var` to `ptr`. 147 148`OPT_STRING(short, long, &str_var, arg_str, description)`:: 149 Introduce an option with string argument. 150 The string argument is put into `str_var`. 151 152`OPT_INTEGER(short, long, &int_var, description)`:: 153 Introduce an option with integer argument. 154 The integer is put into `int_var`. 155 156`OPT_DATE(short, long, &int_var, description)`:: 157 Introduce an option with date argument, see `approxidate()`. 158 The timestamp is put into `int_var`. 159 160`OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)`:: 161 Introduce an option with argument. 162 The argument will be fed into the function given by `func_ptr` 163 and the result will be put into `var`. 164 See 'Option Callbacks' below for a more elaborate description. 165 166`OPT_ARGUMENT(long, description)`:: 167 Introduce a long-option argument that will be kept in `argv[]`. 168 169 170The last element of the array must be `OPT_END()`. 171 172If not stated otherwise, interpret the arguments as follows: 173 174* `short` is a character for the short option 175 (e.g. `\'e\'` for `-e`, use `0` to omit), 176 177* `long` is a string for the long option 178 (e.g. `"example"` for `\--example`, use `NULL` to omit), 179 180* `int_var` is an integer variable, 181 182* `str_var` is a string variable (`char *`), 183 184* `arg_str` is the string that is shown as argument 185 (e.g. `"branch"` will result in `<branch>`). 186 If set to `NULL`, three dots (`...`) will be displayed. 187 188* `description` is a short string to describe the effect of the option. 189 It shall begin with a lower-case letter and a full stop (`.`) shall be 190 omitted at the end. 191 192Option Callbacks 193---------------- 194 195The function must be defined in this form: 196 197 int func(const struct option *opt, const char *arg, int unset) 198 199The callback mechanism is as follows: 200 201* Inside `func`, the only interesting member of the structure 202 given by `opt` is the void pointer `opt->value`. 203 `\*opt->value` will be the value that is saved into `var`, if you 204 use `OPT_CALLBACK()`. 205 For example, do `*(unsigned long *)opt->value = 42;` to get 42 206 into an `unsigned long` variable. 207 208* Return value `0` indicates success and non-zero return 209 value will invoke `usage_with_options()` and, thus, die. 210 211* If the user negates the option, `arg` is `NULL` and `unset` is 1. 212 213Sophisticated option parsing 214---------------------------- 215 216If you need, for example, option callbacks with optional arguments 217or without arguments at all, or if you need other special cases, 218that are not handled by the macros above, you need to specify the 219members of the `option` structure manually. 220 221This is not covered in this document, but well documented 222in `parse-options.h` itself. 223 224Examples 225-------- 226 227See `test-parse-options.c` and 228`builtin-add.c`, 229`builtin-clone.c`, 230`builtin-commit.c`, 231`builtin-fetch.c`, 232`builtin-fsck.c`, 233`builtin-rm.c` 234for real-world examples.