Config::Model::Backend::Augeas(3pm)			User Contributed Perl Documentation		       Config::Model::Backend::Augeas(3pm)

NAME

       Config::Model::Backend::Augeas - Read and write config data through Augeas

SYNOPSIS

	 # model specification with augeas backend
	 {
	  config_class_name => 'OpenSsh::Sshd',

	  # try Augeas and fall-back with custom method
	  read_config  => [ { backend => 'augeas' ,
			      file => '/etc/ssh/sshd_config',
			      # declare "seq" Augeas elements
			      sequential_lens => [/AcceptEnv AllowGroups [etc]/],
			    },
			    { backend => 'custom' , # dir hardcoded in custom class
			      class => 'Config::Model::Sshd'
			    }
			  ],
	  # write_config will be written using read_config specifications

	  element => ...
	 }

DESCRIPTION

       This class provides a way to load or store configuration data through Config::Augeas. This way, the structure and commments of the original
       configuration file will preserved.

       To use Augeas as a backend, you must specify the following "read_config" parameters:

       backend
	   Use "augeas" (or "Augeas")in this case.

       save
	   Either "backup" or "newfile". See "Constructor" in Config::Augeas for details.

       file
	   Name of the configuration file.

       sequential_lens
	   This one is tricky. Set to one when new Augeas list or hash node must be created for each new list or hash element. See "Sequential
	   lens" for details.

       For instance:

	  read_config  => [ { backend => 'augeas' ,
			      save   => 'backup',
			      file => '/etc/ssh/sshd_config',
			      # declare "seq" Augeas elements
			      sequential_lens => [/AcceptEnv AllowGroups/],
			    },
			  ],

   Sequential lens
       Some configuration files feature data that must be written as list or as hash. Depending on the syntax, Augeas list or hash lenses can be
       written so that new "container" nodes are required for each new element.

       For instance, "HostKey" lines can be repeated several times in "sshd_config". Since Augeas must keep track of these several lines, Augeas
       tree will be written like:

	/files/etc/ssh/sshd_config/HostKey[1]
	/files/etc/ssh/sshd_config/HostKey[2]
	/files/etc/ssh/sshd_config/HostKey[3]

       and not:

	/files/etc/ssh/sshd_config/HostKey/1
	/files/etc/ssh/sshd_config/HostKey/2
	/files/etc/ssh/sshd_config/HostKey/3

       The "HostKey" node is created several times. A new hostkey must be added with the following syntax:

	/files/etc/ssh/sshd_config/HostKey[4]

       and not:

	/files/etc/ssh/sshd_config/HostKey/4

       So the "HostKey" lens is sequential.

       The situation is more complex when syntax allow repeated values on several lines. Like:

	AcceptEnv LC_PAPER LC_NAME LC_ADDRESS
	AcceptEnv LC_IDENTIFICATION LC_ALL

       Augeas will have this tree:

	/files/etc/ssh/sshd_config/AcceptEnv[1]/1
	/files/etc/ssh/sshd_config/AcceptEnv[1]/2
	/files/etc/ssh/sshd_config/AcceptEnv[1]/3
	/files/etc/ssh/sshd_config/AcceptEnv[2]/4
	/files/etc/ssh/sshd_config/AcceptEnv[2]/5

       Note that the first index between squarekeeps track of how are grouped the "AcceptEnv" data, but the real list index is after the slash.

       Augeas does not require new elements to create "AcceptEnv[3]". A new element can be added as :

	/files/etc/ssh/sshd_config/AcceptEnv[2]/6

       So this lens is not sequential.

       The same kind of trouble occurs with hash elements. Some hashes tree are like:

	/files/etc/foo/my_hash/my_key1
	/files/etc/foo/my_hash/my_key2

       Others are like:

	/files/etc/foo/my_hash[1]/my_key1
	/files/etc/foo/my_hash[2]/my_key2

       Note that a list-like index is used with the hash key.

       This also depends on the syntax of the configuration file. For instance, "Subsystem" in "sshd_config" can be :

	Subsystem   sftp /usr/lib/openssh/sftp-server
	Subsystem   fooftp /usr/lib/openssh/fooftp-server
	Subsystem   barftp /usr/lib/openssh/barftp-server

       This (unvalid) sshd configuration is represented by:

	/files/etc/ssh/sshd_config/Subsystem[1]/sftp
	/files/etc/ssh/sshd_config/Subsystem[2]/fooftp
	/files/etc/ssh/sshd_config/Subsystem[3]/barftp

       Any new Subsystem must be added with:

	/files/etc/ssh/sshd_config/Subsystem[4]/bazftp

       In this case, the hash is also sequential.

       For these examples, the augeas backend declaration must feature:

	sequential_lens => [qw/HostKey Subsystem/],

   Augeas backend limitation
       The structure and element names of the Config::Model tree must match the structure defined in Augeas lenses. I.e. the order of the element
       declared in Config::Model must match the order required by Augeas lenses.

       Sometimes, the structure of a file loaded by Augeas starts directly with a list of items. For instance "/etc/hosts" structure starts with a
       list of lines that specify hosts and IP addresses. The "set_in" parameter specifies an element name in Config::Model root class that will
       hold the configuration data retrieved by Augeas.

Log and trace
       This module use Log::Log4perl to log debug and info trace with "Data::Read" and "Data::Write" categories.

CAVEATS

       o   Augeas "#comment" nodes are ignored

SEE ALSO

       o   http://augeas.net/ : Augeas project page

       o   Config::Model

       o   Augeas mailing list: http://augeas.net/developers.html

       o   Config::Model mailing list : http://sourceforge.net/mail/?group_id=155650

AUTHOR

       Dominique Dumont, <ddumont at cpan dot org@<gt>

COPYRIGHT

       Copyright (C) 2008-2010 by Dominique Dumont

LICENSE

       This library is free software; you can redistribute it and/or modify it under the LGPL terms.

perl v5.14.2							    2012-07-10				       Config::Model::Backend::Augeas(3pm)