Config::Onion(3) Layered configuration, because configs are like ogres


version 1.006


my $cfg = Config::Onion->new;
my $cfg = Config::Onion->set_default(db => {name => 'foo', password => 'bar'});
my $cfg = Config::Onion->load('/etc/myapp', './myapp');
my $cfg = Config::Onion->load('/etc/myapp', './myapp', {use_ext => 1, filter => \&filter});
my $cfg = Config::Onion->load_glob('./plugins/*');
my $cfg = Config::Onion->load_glob('./plugins/*', {force_plugins => ['Config::Any::YAML']});
$cfg->set_default(font => 'Comic Sans');
$cfg->set_override(font => 'Arial');
my $dbname = $cfg->get->{db}{name};
my $plain_hashref_conf = $cfg->get;
my $dbpassword = $plain_hashref_conf->{db}{password};


All too often, configuration is not a universal or one-time thing, yet most configuration-handling treats it as such. Perhaps you can only load one config file. If you can load more than one, you often have to load all of them at the same time or each is stored completely independently, preventing one from being able to override another. Config::Onion changes that.

Config::Onion stores all configuration settings in four layers: Defaults, Main, Local, and Override. Each layer can be added to as many times as you like. Within each layer, settings which are given multiple times will take the last specified value, while those which are not repeated will remain untouched.

  $cfg->set_default(name => 'Arthur Dent', location => 'Earth');
  $cfg->set_default(location => 'Magrathea');
  # In the Default layer, 'name' is still 'Arthur Dent', but 'location' has
  # been changed to 'Magrathea'.

Regardless of the order in which they are set, values in Main will always override values in the Default layer, the Local layer always overrides both Default and Main, and the Override layer overrides all the others.

The design intent for each layer is:

  • Default

    Hardcoded default values to be used when no further configuration is present

  • Main

    Values loaded from standard configuration files shipped with the application

  • Local

    Values loaded from local configuration files which are kept separate to prevent them from being overwritten by application upgrades, etc.

  • Override

    Settings provided at run-time which take precendence over all configuration files, such as settings provided via command line switches



Returns a new, empty configuration object.

load(@file_stems) =head2 load(@file\_stems, {...})

Loads files matching the given stems using "Config::Any->load_stems" into the Main layer. Also concatenates ``.local'' to each stem and loads matching files into the Local layer. e.g., "$cfg->load('myapp')" would load "myapp.yml" into Main and "myapp.local.js" into Local. All filename extensions supported by "Config::Any" are recognized along with their corresponding formats.

An optional hash ref final argument can be provided to override the default option "use_ext => 1" passed to "Config::Any". All options supported by "Config::Any" are supported except flatten_to_hash. See "Config::Any->load_files" documentation for available options.

load_glob(@globs) =head2 load_glob(@globs, {...})

Uses the Perl "glob" function to expand each parameter into a list of filenames and loads each file using "Config::Any". Files whose names contain the string ``.local.'' are loaded into the Local layer. All other files are loaded into the Main layer.

An optional hash ref final argument can be provided to override the default option "use_ext => 1" passed to "Config::Any". All options supported by "Config::Any" are supported except flatten_to_hash. See "Config::Any->load_files" documentation for available options.

set_default([\%settings,...,] %settings)

set_override([\%settings,...,] %settings)

Imports %settings into the Default or Override layer. Accepts settings both as a plain hash and as hash references, but, if the two are mixed, all hash references must appear at the beginning of the parameter list, before any non-hashref settings.




Returns the complete configuration as a hash reference.





These properties each return a single layer of the configuration. This is not likely to be useful other than for debugging. For most other purposes, you probably want to use "get" instead.


If set, enables the Prefix Structures functionality described below when using the "load" or "load_glob" methods. The value of "prefix_key" specifies the name of the key under which the prefix structure may be found.

Default value is "undef".

Prefix Structures

If you find that your configuration structure is becoming unwieldy due to deeply-nested structures, you can define a file-specific ``prefix structure'' and all other settings within that file will be loaded as children of the prefix structure. For example, if your main program uses

  $cfg = Config::Onion->new(prefix_key => '_prefix');

and "myapp/config.yml" contains

  baz: 1

then $cfg will contain the configuration

      baz: 1

Note that the top-level "prefix_key" is removed.

There are some limitations on the prefix structure, in order to keep it sane and deterministic. First, the prefix structure may only contain hashes. Second, each hash must contain exactly one key. Finally, the value associated with the final key must be left undefined.


No bugs have been reported.

Please report any bugs or feature requests at <>


Dave Sherohman <[email protected]>


This software is copyright (c) 2012 by Lund University Library.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.