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Elektra 0.11.0
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spec is a special namespace that describes via metadata the semantics of individual keys.
Most importantly it:
It is, however, not limited to this but can express any other key database semantics (new plugins might be necessary, though).
The most simple use is to enlist all keys that will be used by an application and maybe give a description for them (we use ini syntax in this document):
So Keys in spec
allow us to specify which keys are read by the application. The description key will be copied (referred to) to folder/anotherkey
of any namespace, so that it can easily be accessed.
Other features are directly implemented in ksLookup
. When cascading keys (those starting with /
) are used following features are now available (in the metadata of respective spec
-keys):
override/#
: use these keys in favor of the key itself (note that #
is the syntax for arrays, e.g. #0
for the first element, #_10
for the 11th and so on)namespace/#
: instead of using all namespaces in the predefined order, one can specify which namespaces should be searched in which orderfallback/#
: when no key was found in any of the (specified) namespaces the fallback
-keys will be searcheddefault
: this value will be used if nothing else was foundE.g.
spec:/sw/app/#0
we specify, that for the key /sw/app/#0/promise
only the namespace user
should be used./somewhere/else
is present, we will use this key instead. The fallback
technique is very powerful: it allows us to have (recursive) links between applications. In the example above, the application is tricked in receiving e.g. the key user:/somewhere/else
when promise
was not available.20
will be used as default, even if no configuration file is found.Note that the fallback, override and cascading works on key level, and not like most other systems have implemented, on configuration file level.
You can tag any key using the check
metadata so that it will be validated.
For example:
In the spec namespace you can also specify mount points. First you need the metakey mountpoint
and a configuration file name. Otherwise, it basically works in the same way as the contracts in plugins using infos
and config
: