Config::Model::Backend::Yaml - Read and write config as a YAML data structure


version 2.121


 use Config::Model ;
 use Data::Dumper ;

 # define configuration tree object
 my $model = Config::Model->new ;
 $model ->create_config_class (
    name => "MyClass",
    element => [ 
        [qw/foo bar/] => { 
            type => 'leaf',
            value_type => 'string'
        baz => { 
            type => 'hash',
            index_type => 'string' ,
            cargo => {
                type => 'leaf',
                value_type => 'string',
  rw_config  => {
    backend => 'yaml',
    config_dir => '/tmp',
    file  => 'foo.yml',
    auto_create => 1,
 ) ;

 my $inst = $model->instance(root_class_name => 'MyClass' );

 my $root = $inst->config_root ;

 my $steps = 'foo=yada bar="bla bla" baz:en=hello
             baz:fr=bonjour baz:hr="dobar dan"';
 $root->load( steps => $steps ) ;
 $inst->write_back ;

Now, /tmp/foo.yml contains:

 bar: bla bla
   en: hello
   fr: bonjour
   hr: dobar dan
 foo: yada


This module is used directly by Config::Model to read or write the content of a configuration tree written with YAML syntax in Config::Model configuration tree.


  • Undefined values are skipped for list element. I.e. if a list element contains ('a',undef,'b'), the data structure contains 'a','b'.

  • YAML file is not created (and may be deleted) when no data is to be written.

Class with only one hash element

If the root node contains a single hash or list element, only the content of this hash is written in a YAML file.

For example, if a class contains:

      element => [
        baz => {
            type => 'hash',
            index_type => 'string' ,
            cargo => {
                type => 'leaf',
                value_type => 'string',

If the configuration is loaded with:

 $root->load("baz:one=un baz:two=deux")

Then the written YAML file does not show baz:

 one: un
 two: deux

Likewise, a YAML file for a class with a single list baz element would be written with:

 - un
 - deux

backend parameter


By default, this module uses YAML::Tiny. This module has the advantage of being light and secure. No Perl object can be created with YAML tags so YAML::Tiny can be used with YAML files coming from unutrusted sources.

On the other hand, YAML::Tiny does not support boolean values: it cannot write true and false as plain scalar. true and false are quoted and are not of type boolean from YAML point of view.

If this is a problem for your configuration files, you can use YAML module which writes true and false without quotes.


new ( node => $node_obj, name => 'yaml' ) ;

Inherited from Config::Model::Backend::Any. The constructor is called by Config::Model::BackendMgr.

read ( io_handle => ... )

Of all parameters passed to this read call-back, only io_handle is used. This parameter must be IO::File object already opened for read.

It can also be undef. In which case read() returns 0.

When a file is read, read() returns 1.

write ( io_handle => ... )

Of all parameters passed to this write call-back, only io_handle is used. This parameter must be IO::File object already opened for write.

write() returns 1.


Dominique Dumont, (ddumont at cpan dot org)


Config::Model, Config::Model::BackendMgr, Config::Model::Backend::Any,


Dominique Dumont


This software is Copyright (c) 2005-2018 by Dominique Dumont.

This is free software, licensed under:

  The GNU Lesser General Public License, Version 2.1, February 1999