NAME

       md_src_plugins_glob_README - README

       • infos = Information about glob plugin is in keys below

       • infos/author = Felix Berlakovich elektra@berlakovich.net

       • infos/licence = BSD

       • infos/needs =

       • infos/ordering = check keytometa

       • infos/stacking = no

       • infos/provides =

       • infos/placements = presetstorage postgetstorage

       • infos/description = copies metadata to keys with the help of globbing

       The glob plugin provides coping metadata given by the plugin's configuration to keys
       identified using glob expressions. Globbing resembles regular expressions. They do not
       have the same expressive power, but are easier to use. The semantics are more suitable to
       match path names:

       • * matches with any key name of just one hierarchy. This means it complies with any
         character except slash or null.

       • ? satisfies single characters with the same exclusions.

       • Additionally, there are ranges and character classes. They can also be inverted.

       So this plugin adds metadata to keys identified by globbing expressions. The plugin copies
       the metadata of the corresponding globbing keys in its configuration. Globbing can be
       applied in get and set direction or both.

   GLOBBING KEYS
       The plugin is configured with globbing keys in its configuration. Each key below the
       configuration is interpreted as a globbing key. The value of the key contains the globbing
       expression. When a key matching the glob expression contained in one of the globbing keys
       is found, the metakeys of the corresponding globbing key are copied.

   GLOBBING DIRECTION
       Globbing keys located directly below the configuration (e.g config/glob/#1) are applied in
       both directions (get and set). Keys below 'get' (e.g. config/glob/get/#1) are applied only
       in the get direction and keys below set (e.g. config/glob/set/#1) are applied only in the
       set direction.

       So the glob plugin iterates over a list of glob expressions for every key. Metadata is
       applied only for the first expression that matches. So later expressions can be used as
       default values.

   GLOBBING FLAGS
       Globbing keys may contain a subkey named 'flags'. This optional key contains the flags to
       be passed to the globbing function (currently fnmatch). If the key does not exist or if
       the value of the key cannot be converted into a number, FNM_PATHNAME is used as a default
       (see fnmatch(3) for more details).

   Contracts
       Glob statements are very useful together with contracts. Storage plugins can request the
       glob plugin to fill up metadata before they receive the keys in elektraPluginSet(). In
       config/needs, the plugin declares which keys should obtain which metadata. If the glob
       expression starts with a slash, the contract checker will automatically prepend the mount
       point.

       For example, the hosts plugin contract contains:

           keyNew ("system/elektra/modules/hosts/config/needs/glob/#1",
                   KEY_VALUE, "/*",
                   KEY_META, "check/ipaddr", "", /* Preferred way to check */
                           /* Can be checked additionally */
                   KEY_META, "check/validation", "^[0-9.:]+$",
                   KEY_META, "check/validation/message",
                           "Character present not suitable for ip address",
                   KEY_END),
           keyNew ("system/elektra/modules/hosts/config/needs/glob/#2",
                   KEY_VALUE, "/*/*",
                           /* Strict character validation */
                   KEY_META, "check/validation", "^[0-9a-zA-Z.:]+$",
                   KEY_META, "check/validation/message",
                           "Character present not suitable for host address",
                   KEY_END),

       We see that the hosts plugin adds two glob statements with the clause config/needs. The
       first one matches with hostnames, the second with aliases.

       The glob plugin only fills the metadata in kdbSet(). This makes a difference compared with
       adding the metadata already in kdbGet(). Using the glob plugin, the user will not see the
       metadata, but later plugins in kdbSet() will.

       To sum up, the glob plugin replenishes the keys with metadata. The plugin applies metadata
       in a flexible way. This metadata can be used for later checks. Limited configuration
       storage plugins, like the hosts plugin, use this feature. They need it because they are
       not able to store metadata themselves. It is obviously not possible to apply values to
       non-existing keys.