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