Does anyone know if there is a way to "transform" specific sections of values instead of replacing the whole value or an attribute?

For example, I've got several appSettings entries that specify the URLs for different webservices. These entries are slightly different in the dev environment than the production environment. Some are less trivial than others

```
<!-- DEV ENTRY -->
<appSettings>
 <add key="serviceName1_WebsService_Url" value="http://wsServiceName1.dev.example.com/v1.2.3.4/entryPoint.asmx" />
 <add key="serviceName2_WebsService_Url" value="http://ma1-lab.lab1.example.com/v1.2.3.4/entryPoint.asmx" />
</appSettings>

<!-- PROD ENTRY -->
<appSettings>
 <add key="serviceName1_WebsService_Url" value="http://wsServiceName1.prod.example.com/v1.2.3.4/entryPoint.asmx" />
 <add key="serviceName2_WebsService_Url" value="http://ws.ServiceName2.example.com/v1.2.3.4/entryPoint.asmx" />
</appSettings>

```

Notice that on the fist entry, the only difference is **".dev" from ".prod".** On the second entry, the subdomain is different: **"ma1-lab.lab1"** from **"ws.ServiceName2"**

So far, I know I can do something like this in the `Web.Release.Config`:

```
<add xdt:Locator="Match(key)" xdt:Transform="SetAttributes(value)" key="serviceName1_WebsService_Url" value="http://wsServiceName1.prod.example.com/v1.2.3.4/entryPoint.asmx" />
<add xdt:Locator="Match(key)" xdt:Transform="SetAttributes(value)" key="serviceName2_WebsService_Url" value="http://ws.ServiceName2.example.com/v1.2.3.4/entryPoint.asmx" />

```

However, every time the Version for that webservice is updated, I would have to update the `Web.Release.Config` as well, which defeats the purpose of simplfying my `web.config` updates.

I know I could also split that URL into different sections and update them independently, but I rather have it all in one key.

I've looked through the available `web.config` Transforms but nothings seems to be geared towars what I am trying to accomplish.

These are the websites I am using as a reference:

[Vishal Joshi's blog](http://vishaljoshi.blogspot.com/2009/03/web-deployment-webconfig-transformation_23.html), [MSDN Help](http://msdn.microsoft.com/en-us/library/dd465326(VS.100).aspx), and [Channel9 video](http://channel9.msdn.com/shows/10-4/10-4-Episode-10-Making-Web-Deployment-Easier/)
['https://Stackoverflow.com/questions/2915329', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/80268/']
As a matter of fact you can do this, but it is not as easy as you might think. You can create your own config transformation. I have just written a very detailed blog post at <http://sedodream.com/2010/09/09/ExtendingXMLWebconfigConfigTransformation.aspx> regarding this. But here are the hightlights:

* Create Class Library project
* Reference Web.Publishing.Tasks.dll *(under %Program Files (x86)%MSBuild\Microsoft\VisualStudio\v10.0\Web folder)*
* Extend Microsoft.Web.Publishing.Tasks.Transform class
* Implement the Apply() method
* Place the assembly in a well known location
* Use xdt:Import to make the new transform available
* Use transform

**Here is the class I created to do this replace**

```
namespace CustomTransformType
{
    using System;
    using System.Text.RegularExpressions;
    using System.Xml;
    using Microsoft.Web.Publishing.Tasks;

    public class AttributeRegexReplace : Transform
    {
        private string pattern;
        private string replacement;
        private string attributeName;

        protected string AttributeName
        {
            get
            {
                if (this.attributeName == null)
                {
                    this.attributeName = this.GetArgumentValue("Attribute");
                }
                return this.attributeName;
            }
        }
        protected string Pattern
        {
            get
            {
                if (this.pattern == null)
                {
                    this.pattern = this.GetArgumentValue("Pattern");
                }

                return pattern;
            }
        }

        protected string Replacement
        {
            get
            {
                if (this.replacement == null)
                {
                    this.replacement = this.GetArgumentValue("Replacement");
                }

                return replacement;
            }
        }

        protected string GetArgumentValue(string name)
        {
            // this extracts a value from the arguments provided
            if (string.IsNullOrWhiteSpace(name)) 
            { throw new ArgumentNullException("name"); }

            string result = null;
            if (this.Arguments != null && this.Arguments.Count > 0)
            {
                foreach (string arg in this.Arguments)
                {
                    if (!string.IsNullOrWhiteSpace(arg))
                    {
                        string trimmedArg = arg.Trim();
                        if (trimmedArg.ToUpperInvariant().StartsWith(name.ToUpperInvariant()))
                        {
                            int start = arg.IndexOf('\'');
                            int last = arg.LastIndexOf('\'');
                            if (start <= 0 || last <= 0 || last <= 0)
                            {
                                throw new ArgumentException("Expected two ['] characters");
                            }

                            string value = trimmedArg.Substring(start, last - start);
                            if (value != null)
                            {
                                // remove any leading or trailing '
                                value = value.Trim().TrimStart('\'').TrimStart('\'');
                            }
                            result = value;
                        }
                    }
                }
            }
            return result;
        }

        protected override void Apply()
        {
            foreach (XmlAttribute att in this.TargetNode.Attributes)
            {
                if (string.Compare(att.Name, this.AttributeName, StringComparison.InvariantCultureIgnoreCase) == 0)
                {
                    // get current value, perform the Regex
                    att.Value = Regex.Replace(att.Value, this.Pattern, this.Replacement);
                }
            }
        }
    }
}

```

**Here is web.config**

```
<?xml version="1.0"?>
<configuration>
  <appSettings>
    <add key="one" value="one"/>
    <add key="two" value="partial-replace-here-end"/>
    <add key="three" value="three here"/>
  </appSettings>
</configuration>

```

Here is my config transform file

```
<?xml version="1.0"?>

<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">

  <xdt:Import path="C:\Program Files (x86)\MSBuild\Custom\CustomTransformType.dll"
              namespace="CustomTransformType" />

  <appSettings>
    <add key="one" value="one-replaced" 
         xdt:Transform="Replace" 
         xdt:Locator="Match(key)" />
    <add key="two" value="two-replaced" 
         xdt:Transform="AttributeRegexReplace(Attribute='value', Pattern='here',Replacement='REPLACED')" 
         xdt:Locator="Match(key)"/>
  </appSettings>
</configuration>

```

**Here is the result after transformation**

```
<?xml version="1.0"?>
<configuration>
  <appSettings>
    <add key="one" value="one-replaced"/>
    <add key="two" value="partial-replace-REPLACED-end"/>
    <add key="three" value="three here"/>
  </appSettings>
</configuration>

```
Just as an update, if you're using Visual Studio 2013, you should reference %Program Files (x86)%MSBuild\Microsoft\VisualStudio\v12.0\Web\Microsoft.Web.XmlTransform.dll instead.