Xml File Preprocessor

Overview

This tool can be used to preprocess an XML file and deploy it to a target environment making appropriate environment specific substitutions.

Goals

Not have to maintain multiple configuration files or templates of configuration files for different environments. In other words, to have a single source of truth.
Keep the original source of truth configuration file fully operational for development. Developers should be able to get the file directly from source control and run without having to make changes to it.

This is accomplished by decorating the configuration files with non-breaking comments that contain instructions for the preprocessor.

Examples

For example if you want to turn debug page compilation off when in production, you might do something like this:

<configuration>
  <system.web>
    <!-- ifdef ${production} -->
    <!-- <compilation defaultLanguage="c#" debug="false"/> -->
    <!-- else -->
    <compilation defaultLanguage="c#" debug="true"/>
    <!-- endif -->
  </system.web>
</configuration>

The debug setting will remain true for an unprocessed file, but when this file is deployed using the XmlPreprocess tool with the "production" property defined, the ifdef condition will be tested, and if true, the comments around its body content will be removed, and the else branch will be omitted entirely. This will render the following:

<configuration>
  <system.web>
    <compilation defaultLanguage="c#" debug="false"/>
  </system.web>
</configuration>

Another powerful way to use the preprocessor is to substitute properties into placeholders in your XML file much like in Ant or NAnt. Properties can be defined in an external XML file or passed on the command line to XmlPreprocess.exe.

For example if you have an application setting that contains the name of a remote server, but the name of that server changes from environment to environment, you may want to mark-up your XML like this:

<configuration>
  <appSettings>
    <!-- ifdef ${_xml_preprocess} -->
    <!-- <add key="server" value="${remoteserver}"/> -->
    <!-- else -->
    <add key="server" value="developmentserver1"/>
    <!-- endif -->
  </appSettings>
</configuration>

Then you can provide the value for the "remoteserver" property at deployment time via the commandline or external settings file. For more information see properties.