Plugins/TGenshi

  1. TGenshi Templating Plugin
    1. Inside of templates
    2. Examples
      1. Examples: Old Genshi Syntax
        1. Group Negation
    3. FAQs

TGenshi Templating Plugin

This document reflects the TGenshi plugin in bcfg2 0.9.5 and later. This plugin works with version 0.4 and newer of the genshi library.

The TGenshi plugin allows you to use the Genshi templating system to create files, instead of the various diff-based methods offered by the Cfg plugin. It also allows you to include the results of probes executed on the client in the created files.

To begin, you will need to download and install the Genshi templating engine.

To install on CentOS or RHEL 5, run: 

sudo yum install python-genshi

Once it is installed, you can enable it by adding TGenshi to the generators line in /etc/bcfg2.conf on your Bcfg server. For example: 

generators = SSHbase,Cfg,Pkgmgr,Svcmgr,Rules,TGenshi

The TGenshi plugin makes use of a Cfg-like directory structure located in in a TGenshi subdirectory of your repository, usually /var/lib/bcfg2/TGenshi. Each file has a directory containing two file types, template and info. Templates are named according to the genshi format used; template.txt uses the genshi text format, and template.xml uses the XML format.

As of Bcfg2 0.9.6 if used with Genshi 0.5 or later the plugin also supports the new style text template format for files named template.newtxt. One of the advantages of the new format is that it does not use # as a command delimiter, making it easier to utilize for configuration files that use # as a comment character.

Only one template format may be used per file served. Info files are identical to those used in Cfg, and info.xml files are supported.

Inside of templates

  • metadata is the client's metadata
  • properties.properties is an xml document of unstructured data

See the genshi documentation for examples of Genshi syntax.

Examples

See Plugins/TGenshi/examples for some TGenshi template examples, including the great starting point /etc/motd. They will use the new style of Genshi syntax, unless noted otherwise.

Examples: Old Genshi Syntax

Genshi's web pages recommend against using this syntax, as it may disappear from future releases.

Group Negation

editor's note: This section needs to be moved to TGenshi/examples and updated to show new style

Templates are also useful for cases where more sophisticated boolean operations than those supported by Cfg are needed. For example, the template: 

#if "ypbound" in metadata.groups and "workstation" in metadata.groups
client is ypbound workstation
#end
#if "ubuntu" not in metadata.groups and "desktop" in metadata.groups
client is a desktop, but not an ubuntu desktop
#end

Produces: 

<ConfigFile name="/bar.conf" owner="root" perms="0644" group="root">client is ypbound workstation
client is a desktop, but not an ubuntu desktop
</ConfigFile>

This flexibility provides the ability to build much more compact and succinct definitions of configuration contents than Cfg can.

FAQs

Question: How do I escape the $ (dollar sign) in a TGenshi text template? For example, if I want to include SVN (subversion) keywords like $Id$ or $HeadURL$ in TGenshi-generated files, or am templating a bourne shell (sh/bash) script or Makefile (make).

Answer: Use $$ (double dollar sign) to output a literal $ (dollarsign) in a TGenshi text template. So instead of $Id$, you'd use $$Id$$. See also Genshi tickets #282: Document $$ escape convention and #283: Allow for redefinition of template syntax per-file.