Ubuntu Manpage: md_doc_help_elektra-cascading - elektra-cascading(7) -- of key names Cascading is the triggering of

NAME

md_doc_help_elektra-cascading - elektra-cascading(7) -- of key names Cascading is the triggering of
secondary actions. For configuration it means that first the user configuration is read and if this
attempt fails, the system configuration is used as fallback.

The idea is that the application installs a configuration storage with default settings that can only be
changed by the administrator. But every user has the possibility to override parts of this system
configuration regarding the user's needs in the *user configuration. To sum up, besides system
configuration, users have their own key databases that can override the settings according to their
preferences.

Thus when a key starts with / such cascading will automatically performed.

Keys in spec allow us to specify which keys are read by the application, which fallback it might have and
which is the default value using meta data. The implementation of these features happened in ksLookup.
When cascading keys (those starting with /) are used following features are available (in the meta data
of respective spec-keys):

• override/#: use these keys in favour 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 order

• fallback/#: when no key was found in any of the (specified) namespaces the fallback-keys will be
searched

• default: this value will be used if nothing else was found

CASCADING
When cascading keys (those starting with /) the lookup will work in the following way (it can be debugged
with kdb get -v):

1.) In the spec-key the override/# keys will be considered. 2.) If, in the spec-key, a namespace/# exist,
those namespaces will be used. 3.) Otherwise, all namespaces will be considered, see here. 4.) In the
spec-key the fallback/# keys will be considered. 5.) In the spec-key the default value will be returned.

See application integration for how to use cascading names in the context of applications.