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XmlConfigMerge - Merge config file settings

, 6 Nov 2006
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Supports merging of .config file settings, such as in a push to staging-server deployment environment. Also supports XPath updates. Class library and Console app provided.


When deploying .NET applications, it is often desirable to "merge" configuration settings between a "distribution" .config file and an existing .config file.

This is particularly useful when new config parameters are added to a "distribution" config file, and an existing .config file (such as on an already-configured server) must have these new parameters added, while preserving existing parameter settings.

The XmlConfigMerge utility (provided both as a library assembly and as a console application) supports this merging of XML .config files, and also supports setting of specific parameters via XPath filtering and optional Regex pattern matching.

Example Usage Scenarios

  • Code Promotion: Push release from development to staging: Use to add newly-added development parameters while preserving existing staging parameters. (See "Example C# Code" below.)
  • Publisher Policy Files: Set the binding redirect parameters such that the AssemblyVersion in the latest build is specified (see "Example C# Code within a NAnt script" below.)
  • Windows Installer Packages: Maintain existing application .config settings (from a prior install).

Example C# Code

//Merge an "existing" config's settings into a "distrib" config, 
//writing out results to "existing" config
ConfigFileManager config = new ConfigFileManager(DistribConfigFile,
        true); //makeMergeFromConfigPathTheSavePath

//Regex pattern replace having single regex group to be replaced within
//pattern, matching multiple config items
        new Regex(@"http://(.*)/service.ashx") );

//appsettings key-value pair set for existing param. 
//It is created if it does not exist.


Example C# Code within a NAnt script

<!-- Set the publisher-policy file newVersion attribute -->

<property value="policyTheAssemblyName.xml" name="policyFileName"/>
<property value="" name="policyAssemblyVersion"/>
<script language="C#">
        public static void ScriptMain(Project project) {
            policyFileName = project.Properties["policyFileName"];
            project.Log(Level.Info, "Modifying policy file: " + 

            ConfigFileManager config = 
                  new ConfigFileManager(policyFileName);
            LogInfoLines(project, config.ReplaceXPathValues(
                    project.Properties["policyAssemblyVersion"] ) );
        private static void LogInfoLines(Project project, 
                                         string[] lines) {
            foreach (string line in lines) {
                project.Log(Level.Info, line);
        <includes name="${nant.location}\XmlConfigMerge.dll"/>
        <import name="Tools.XmlConfigMerge"/>

Example Command-Line

XmlConfigMergeConsole.exe "..\MergeDistribConfigFiles\web.config" 
-m "..\MergeExistingConfigFiles\web.config" -mwritten
-r "//@value" "QAServer/QAVirtDir1" "http://(.*)/service.ashx"
-r "/configuration/appSettings/add[@key='param2']/@value" "QA-value2"

Further Examples

See the included unit-tests (utilizing NUnit) for additional usage examples.

Release Notes

  • Version 1.3 - 11/06/2006: Changed to use share mode on file opens, added error handling.
  • Version 1.2: Fix for master child nodes not being preserved when not present in merge-from doc.
  • Version 1.1: Handles duplicate appSettings keys in a manner consistent with System.Configuration (uses last one); added precondition checks.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

Web Developer
United States United States
.NET solution architect / developer based in Chicago.

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Comments and Discussions

QuestionLicensing question PinmemberMember 109324338-Jul-14 3:56 
QuestionHelpful tool Pinmembermmsharp11-Nov-13 11:04 
QuestionVery good useful tool! PinmemberDavid O. Lavallee9-Dec-11 8:10 
QuestionVery useful tool! PinmemberDavid O. Lavallee9-Dec-11 8:00 
GeneralDid you hear something about DotNet.Helper Project Pinmembervoid leenux();15-Apr-11 3:04 
GeneralThanks a lot! Pinmemberhumanier26-Aug-10 4:47 
QuestionUsing this at runtime, how do you refresh the config file to reflect the changes? PinmemberLeon v Wyk10-Oct-08 4:05 
QuestionNAnt and msi's? Pinmemberrobrich6-Nov-06 10:32 
GeneralXML Diff and Patch GUI Tool PinmemberChristian Birkl26-Sep-06 8:17 
GeneralGood tool PinmemberMark Focas29-Jun-04 20:41 
GeneralAvoiding problems with schemas PinsussAriel Erenberg28-Jun-04 1:31 
GeneralRe: Avoiding problems with schemas Pinmemberbuc3-Jul-04 10:57 
GeneralRe: Avoiding problems with schemas Pinmemberthanigaivelanb23-Jan-09 0:03 

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