Elektra serves as a universal and secure framework to access configuration parameters in a global, hierarchical key database and provides a mature, consistent and easily comprehensible API. Its modularity effectively avoids code duplication across applications and tools regarding configuration tasks. Elektra abstracts from cross-platform-related issues and allows applications to be aware of other applications' configurations, leveraging easy application integration.
See the readme for more introduction. See the glossary for the used terminology.
This document's main goal is to describe the API. It covers:
- external C-API (see Modules above), which are the essential core parts
- C++-API (see Data Structures above) from a direct binding to high-level functionality, such as mounting functionality
- plugins API, see @ref Plugins
- all other documentation of Elektra (see Related Pages next to Main Page)
On the one hand it gives an overview and an introduction for developers using Elektra, on the other hand it gives an informal description what methods must and may provide to allow an alternative implementation of the API.
The latest released version (for stable releases) of this document can be found at https://doc.libelektra.org/api/latest/html
The git master version of this document can be found at https://doc.libelektra.org/api/master/html
Important: On GitHub links to API functions are broken, so it is recommended that you continue reading in one of these links above.
A C or C++ source file that wants to use Elektra should include:
#include <kdb.h>
To link an executable with the Elektra library, one way is to
use the pkg-config
tool:
gcc -o application `pkg-config --cflags --libs elektra` application.c
Another way is to use CMake:
find_package(Elektra REQUIRED)
include_directories (${ELEKTRA_INCLUDE_DIR})
target_link_libraries (application ${ELEKTRA_LIBRARIES})
Read about compiling elektra.
List of all available Plugins and get started by developing your own plugins @ref plugin.
The API was written in pure C because Elektra was designed to be useful even for the most basic system programs.
The API follows an object-oriented design, and there are 3 main classes as shown by the figure:
Some general things you can do with each class are:
[KDB (Key Database)](@ref kdb)
- [Open](@ref kdbOpen) and [Close](@ref kdbClose) the Key Database
- [Get](@ref kdbGet) and [Set](@ref kdbSet) [KeySet](@ref keyset) in the Key Database
- See [class documentation](@ref kdb) for more
[Key](@ref key)
- [Create](@ref keyNew) and [Delete](@ref keyDel)
- Get and Set key the [name](@ref keySetName)
- Get and Set [string](@ref keySetString) or [binary](@ref keySetBinary) values
- Get and Set [Meta Data](@ref keymeta)
- See [class documentation](@ref key) for more
[KeySet](@ref keyset)
- [Create](@ref ksNew) and [Delete](@ref ksDel)
- Append [a single key](@ref ksAppendKey) or an entire [KeySet](@ref ksAppend)
- [Lookup keys](@ref ksLookup)
- Pop [the last key](@ref ksPop), [a key by name](@ref ksLookup), or [every key](@ref ksCopy)
- [Work with](@ref ksNext) its [internal cursor](@ref ksCurrent)
- See [class documentation](@ref keyset) for more
More background information about the classes
There are 5 trees (=namespaces) of keys: spec
, proc
, dir
, user
and system
that are all unified (in the given order) in one cascading tree starting with /
.
The cascading tree is the logical tree to be used in applications. The other trees are the physical ones that stem from configuration sources. When using cascading key the best key will be searched at run-time, which appears like a tree on its own. See @ref cascading in the documentation of ksLookupByName() on how the selection of keys works.
-
The
spec
treeThis tree specifies how the lookup should take place and also allows us to define defaults or document a key. The metadata of a key contains this information:
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 thefallback
-keys will be searcheddefault
: this value will be used if nothing else was found
-
The
proc
treeIs the only read-only tree. The configuration does not stem from the [KDB (Key Database)](@ref kdb), but any other source, e.g. command-line arguments or environment.
-
The
dir
treeAllows us to have a per-directory overwrite of configuration files, e.g. for project specific settings.
-
The
user
treeUsed to store user-specific configurations, like the personal settings of a user to certain programs. The user subtree will always be favored if present (except for security concerns the user subtree may not be considered).
-
The
system
treeIt is provided to store system-wide configuration keys, that is, the last fallback for applications but the only resort for daemons and system services.
Read more about namespaces and a tutorial for namespaces.
When using Elektra to store your application's configuration and state, please keep in mind the following rules:
- You are not allowed to create keys right under the root. They are reserved for more generic purposes.
- The keys for your application, called say myapp, should be created under
/sw/org/myapp/#0/current
- sw is for software
- org is the organization. For uniqueness a full reverse url encoded with '/' instead of '.' is useful.
#0
is the major version of the configuration- current is the default configuration profile.
- That means you just need to kdbGet()
/sw/org/myapp/#0/profile
and then ksLookupByName() in/sw/org/myapp/#0/profile/key
where profile is from command-line arguments and defaults to current.
Read more about key names
The core of Elektra does not store configuration itself to the hard disk. Instead this work is delegated to backends.
If you want to develop a backend, you should already have some experience with Elektra from the user point of view. You should be familiar with the data structures: [Key](@ref key) and [KeySet](@ref keyset) Then you can start reading about Backends that are composed out of [Plugins](@ref plugin). To get started with writing plugins, first read our plugin tutorial and then lookup details in the API description in @ref plugin.
Read more about mounting
- See elektra-glossary(7)
- More information about elektra-backends(7)
- More information about plugins-framework