# NAME

Config::Onion - Layered configuration, because configs are like ogres

# VERSION

version 1.007

# SYNOPSIS

    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->load('config');
    $cfg->load_glob('conf.d/myapp*');
    $cfg->set_override(font => 'Arial');

    my $dbname = $cfg->get->{db}{name};
    my $plain_hashref_conf = $cfg->get;
    my $dbpassword = $plain_hashref_conf->{db}{password};

# DESCRIPTION

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

If a higher-priority layer wishes to completely remove a hash entry made by a
lower-priority layer (i.e., delete the hash key, not just set it to an empty
value), it can do so by setting the value to "!DELETE!".  This only applies to
hash entries, not array values, as the entire array already needs to be
overwritten to make any changes to it.  Also, if, for some reason, the
configuration contains objects, the contents of those objects will be ignored
for the sake of encapsulation.  Only unblessed hashes are cleaned in this
manner.

# METHODS

## new

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.

# PROPERTIES

## cfg

## get

Returns the complete configuration as a hash reference.

## default

## main

## local

## override

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.

## prefix\_key

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');
    $cfg->load("myapp/config");

and `myapp/config.yml` contains

    _prefix:
      foo:
        bar:

    baz: 1

then `$cfg` will contain the configuration

    foo:
      bar:
        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.

# BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests at
[https://github.com/dsheroh/Config-Onion/issues](https://github.com/dsheroh/Config-Onion/issues)

# AUTHOR

Dave Sherohman <dsheroh@cpan.org>

# COPYRIGHT AND LICENSE

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.