Updating web.config Settings with MsBuild

I've slightly stolen this technique from Sayed I. Hashimi and this blog post.

Changing web.config settings between environments can be a chore which is mostly relieved by creating different versions specific to each environment and letting the process take care of replacing values at build time. Typically we have a web.Debug.config and a web.Release.config, each associated with a build configuration.

Usually, local developer builds also need some personalisation of these settings to reference their own environment (paths, keys, database connections) but usually not the kind of thing you want committing to source control.

Here I've used the XmlPoke task to find the correct part of the web.config (or any app.config for that matter) and change the value of a setting.

So for a .config file containing this:

We can use MsBuild's batching feature to create a list of settings that can be changed in a single file.


//add[@key='hello']/@value again //add[@key='mynameis']/@value alice

Here we're using metadata on each ItemGroup to keep a pair of variables together for each replacement, the xpath query to the setting and the value to substitute. Each XmlConfigChange object is evaluated against $(MyConfig) in turn and updates the config using the new value. So, after the script runs we should have: