Documentation/technical/api-config.txt

   1 config API
   2 ==========
   3
   4 The config API gives callers a way to access Git configuration files
   5 (and files which have the same syntax). See linkgit:git-config[1] for a
   6 discussion of the config file syntax.
   7
   8 General Usage
   9 -------------
  10
  11 Config files are parsed linearly, and each variable found is passed to a
  12 caller-provided callback function. The callback function is responsible
  13 for any actions to be taken on the config option, and is free to ignore
  14 some options. It is not uncommon for the configuration to be parsed
  15 several times during the run of a Git program, with different callbacks
  16 picking out different variables useful to themselves.
  17
  18 A config callback function takes three parameters:
  19
  20 - the name of the parsed variable. This is in canonical "flat" form: the
  21   section, subsection, and variable segments will be separated by dots,
  22   and the section and variable segments will be all lowercase. E.g.,
  23   `core.ignorecase`, `diff.SomeType.textconv`.
  24
  25 - the value of the found variable, as a string. If the variable had no
  26   value specified, the value will be NULL (typically this means it
  27   should be interpreted as boolean true).
  28
  29 - a void pointer passed in by the caller of the config API; this can
  30   contain callback-specific data
  31
  32 A config callback should return 0 for success, or -1 if the variable
  33 could not be parsed properly.
  34
  35 Basic Config Querying
  36 ---------------------
  37
  38 Most programs will simply want to look up variables in all config files
  39 that Git knows about, using the normal precedence rules. To do this,
  40 call `git_config` with a callback function and void data pointer.
  41
  42 `git_config` will read all config sources in order of increasing
  43 priority. Thus a callback should typically overwrite previously-seen
  44 entries with new ones (e.g., if both the user-wide `~/.gitconfig` and
  45 repo-specific `.git/config` contain `color.ui`, the config machinery
  46 will first feed the user-wide one to the callback, and then the
  47 repo-specific one; by overwriting, the higher-priority repo-specific
  48 value is left at the end).
  49
  50 The `git_config_with_options` function lets the caller examine config
  51 while adjusting some of the default behavior of `git_config`. It should
  52 almost never be used by "regular" Git code that is looking up
  53 configuration variables. It is intended for advanced callers like
  54 `git-config`, which are intentionally tweaking the normal config-lookup
  55 process. It takes two extra parameters:
  56
  57 `filename`::
  58 If this parameter is non-NULL, it specifies the name of a file to
  59 parse for configuration, rather than looking in the usual files. Regular
  60 `git_config` defaults to `NULL`.
  61
  62 `respect_includes`::
  63 Specify whether include directives should be followed in parsed files.
  64 Regular `git_config` defaults to `1`.
  65
  66 Reading Specific Files
  67 ----------------------
  68
  69 To read a specific file in git-config format, use
  70 `git_config_from_file`. This takes the same callback and data parameters
  71 as `git_config`.
  72
  73 Querying For Specific Variables
  74 -------------------------------
  75
  76 For programs wanting to query for specific variables in a non-callback
  77 manner, the config API provides two functions `git_config_get_value`
  78 and `git_config_get_value_multi`. They both read values from an internal
  79 cache generated previously from reading the config files.
  80
  81 `int git_config_get_value(const char *key, const char **value)`::
  82
  83         Finds the highest-priority value for the configuration variable `key`,
  84         stores the pointer to it in `value` and returns 0. When the
  85         configuration variable `key` is not found, returns 1 without touching
  86         `value`. The caller should not free or modify `value`, as it is owned
  87         by the cache.
  88
  89 `const struct string_list *git_config_get_value_multi(const char *key)`::
  90
  91         Finds and returns the value list, sorted in order of increasing priority
  92         for the configuration variable `key`. When the configuration variable
  93         `key` is not found, returns NULL. The caller should not free or modify
  94         the returned pointer, as it is owned by the cache.
  95
  96 `void git_config_clear(void)`::
  97
  98         Resets and invalidates the config cache.
  99
 100 The config API also provides type specific API functions which do conversion
 101 as well as retrieval for the queried variable, including:
 102
 103 `int git_config_get_int(const char *key, int *dest)`::
 104
 105         Finds and parses the value to an integer for the configuration variable
 106         `key`. Dies on error; otherwise, stores the value of the parsed integer in
 107         `dest` and returns 0. When the configuration variable `key` is not found,
 108         returns 1 without touching `dest`.
 109
 110 `int git_config_get_ulong(const char *key, unsigned long *dest)`::
 111
 112         Similar to `git_config_get_int` but for unsigned longs.
 113
 114 `int git_config_get_bool(const char *key, int *dest)`::
 115
 116         Finds and parses the value into a boolean value, for the configuration
 117         variable `key` respecting keywords like "true" and "false". Integer
 118         values are converted into true/false values (when they are non-zero or
 119         zero, respectively). Other values cause a die(). If parsing is successful,
 120         stores the value of the parsed result in `dest` and returns 0. When the
 121         configuration variable `key` is not found, returns 1 without touching
 122         `dest`.
 123
 124 `int git_config_get_bool_or_int(const char *key, int *is_bool, int *dest)`::
 125
 126         Similar to `git_config_get_bool`, except that integers are copied as-is,
 127         and `is_bool` flag is unset.
 128
 129 `int git_config_get_maybe_bool(const char *key, int *dest)`::
 130
 131         Similar to `git_config_get_bool`, except that it returns -1 on error
 132         rather than dying.
 133
 134 `int git_config_get_string_const(const char *key, const char **dest)`::
 135
 136         Allocates and copies the retrieved string into the `dest` parameter for
 137         the configuration variable `key`; if NULL string is given, prints an
 138         error message and returns -1. When the configuration variable `key` is
 139         not found, returns 1 without touching `dest`.
 140
 141 `int git_config_get_string(const char *key, char **dest)`::
 142
 143         Similar to `git_config_get_string_const`, except that retrieved value
 144         copied into the `dest` parameter is a mutable string.
 145
 146 `int git_config_get_pathname(const char *key, const char **dest)`::
 147
 148         Similar to `git_config_get_string`, but expands `~` or `~user` into
 149         the user's home directory when found at the beginning of the path.
 150
 151 `git_die_config(const char *key, const char *err, ...)`::
 152
 153         First prints the error message specified by the caller in `err` and then
 154         dies printing the line number and the file name of the highest priority
 155         value for the configuration variable `key`.
 156
 157 `void git_die_config_linenr(const char *key, const char *filename, int linenr)`::
 158
 159         Helper function which formats the die error message according to the
 160         parameters entered. Used by `git_die_config()`. It can be used by callers
 161         handling `git_config_get_value_multi()` to print the correct error message
 162         for the desired value.
 163
 164 See test-config.c for usage examples.
 165
 166 Value Parsing Helpers
 167 ---------------------
 168
 169 To aid in parsing string values, the config API provides callbacks with
 170 a number of helper functions, including:
 171
 172 `git_config_int`::
 173 Parse the string to an integer, including unit factors. Dies on error;
 174 otherwise, returns the parsed result.
 175
 176 `git_config_ulong`::
 177 Identical to `git_config_int`, but for unsigned longs.
 178
 179 `git_config_bool`::
 180 Parse a string into a boolean value, respecting keywords like "true" and
 181 "false". Integer values are converted into true/false values (when they
 182 are non-zero or zero, respectively). Other values cause a die(). If
 183 parsing is successful, the return value is the result.
 184
 185 `git_config_bool_or_int`::
 186 Same as `git_config_bool`, except that integers are returned as-is, and
 187 an `is_bool` flag is unset.
 188
 189 `git_config_maybe_bool`::
 190 Same as `git_config_bool`, except that it returns -1 on error rather
 191 than dying.
 192
 193 `git_config_string`::
 194 Allocates and copies the value string into the `dest` parameter; if no
 195 string is given, prints an error message and returns -1.
 196
 197 `git_config_pathname`::
 198 Similar to `git_config_string`, but expands `~` or `~user` into the
 199 user's home directory when found at the beginning of the path.
 200
 201 Include Directives
 202 ------------------
 203
 204 By default, the config parser does not respect include directives.
 205 However, a caller can use the special `git_config_include` wrapper
 206 callback to support them. To do so, you simply wrap your "real" callback
 207 function and data pointer in a `struct config_include_data`, and pass
 208 the wrapper to the regular config-reading functions. For example:
 209
 210 -------------------------------------------
 211 int read_file_with_include(const char *file, config_fn_t fn, void *data)
 212 {
 213         struct config_include_data inc = CONFIG_INCLUDE_INIT;
 214         inc.fn = fn;
 215         inc.data = data;
 216         return git_config_from_file(git_config_include, file, &inc);
 217 }
 218 -------------------------------------------
 219
 220 `git_config` respects includes automatically. The lower-level
 221 `git_config_from_file` does not.
 222
 223 Custom Configsets
 224 -----------------
 225
 226 A `config_set` can be used to construct an in-memory cache for
 227 config-like files that the caller specifies (i.e., files like `.gitmodules`,
 228 `~/.gitconfig` etc.). For example,
 229
 230 ---------------------------------------
 231 struct config_set gm_config;
 232 git_configset_init(&gm_config);
 233 int b;
 234 /* we add config files to the config_set */
 235 git_configset_add_file(&gm_config, ".gitmodules");
 236 git_configset_add_file(&gm_config, ".gitmodules_alt");
 237
 238 if (!git_configset_get_bool(gm_config, "submodule.frotz.ignore", &b)) {
 239         /* hack hack hack */
 240 }
 241
 242 /* when we are done with the configset */
 243 git_configset_clear(&gm_config);
 244 ----------------------------------------
 245
 246 Configset API provides functions for the above mentioned work flow, including:
 247
 248 `void git_configset_init(struct config_set *cs)`::
 249
 250         Initializes the config_set `cs`.
 251
 252 `int git_configset_add_file(struct config_set *cs, const char *filename)`::
 253
 254         Parses the file and adds the variable-value pairs to the `config_set`,
 255         dies if there is an error in parsing the file. Returns 0 on success, or
 256         -1 if the file does not exist or is inaccessible. The user has to decide
 257         if he wants to free the incomplete configset or continue using it when
 258         the function returns -1.
 259
 260 `int git_configset_get_value(struct config_set *cs, const char *key, const char **value)`::
 261
 262         Finds the highest-priority value for the configuration variable `key`
 263         and config set `cs`, stores the pointer to it in `value` and returns 0.
 264         When the configuration variable `key` is not found, returns 1 without
 265         touching `value`. The caller should not free or modify `value`, as it
 266         is owned by the cache.
 267
 268 `const struct string_list *git_configset_get_value_multi(struct config_set *cs, const char *key)`::
 269
 270         Finds and returns the value list, sorted in order of increasing priority
 271         for the configuration variable `key` and config set `cs`. When the
 272         configuration variable `key` is not found, returns NULL. The caller
 273         should not free or modify the returned pointer, as it is owned by the cache.
 274
 275 `void git_configset_clear(struct config_set *cs)`::
 276
 277         Clears `config_set` structure, removes all saved variable-value pairs.
 278
 279 In addition to above functions, the `config_set` API provides type specific
 280 functions in the vein of `git_config_get_int` and family but with an extra
 281 parameter, pointer to struct `config_set`.
 282 They all behave similarly to the `git_config_get*()` family described in
 283 "Querying For Specific Variables" above.
 284
 285 Writing Config Files
 286 --------------------
 287
 288 Git gives multiple entry points in the Config API to write config values to
 289 files namely `git_config_set_in_file` and `git_config_set`, which write to
 290 a specific config file or to `.git/config` respectively. They both take a
 291 key/value pair as parameter.
 292 In the end they both call `git_config_set_multivar_in_file` which takes four
 293 parameters:
 294
 295 - the name of the file, as a string, to which key/value pairs will be written.
 296
 297 - the name of key, as a string. This is in canonical "flat" form: the section,
 298   subsection, and variable segments will be separated by dots, and the section
 299   and variable segments will be all lowercase.
 300   E.g., `core.ignorecase`, `diff.SomeType.textconv`.
 301
 302 - the value of the variable, as a string. If value is equal to NULL, it will
 303   remove the matching key from the config file.
 304
 305 - the value regex, as a string. It will disregard key/value pairs where value
 306   does not match.
 307
 308 - a multi_replace value, as an int. If value is equal to zero, nothing or only
 309   one matching key/value is replaced, else all matching key/values (regardless
 310   how many) are removed, before the new pair is written.
 311
 312 It returns 0 on success.
 313
 314 Also, there are functions `git_config_rename_section` and
 315 `git_config_rename_section_in_file` with parameters `old_name` and `new_name`
 316 for renaming or removing sections in the config files. If NULL is passed
 317 through `new_name` parameter, the section will be removed from the config file.