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)