How do I read/write App.config settings with PowerShell?

Question

I'd like to use PowerShell as part of our automated build process to update an App.config file while deploying into our test environment. How can I do this?

Answer 1

Given this sample App.config: C:\Sample\App.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
     <add name="dbConnectionString" 
       connectionString="Data Source=(local);Initial Catalog=Northwind;Integrated Security=True"/>
    </connectionStrings>
</configuration>

The following script, C:\Sample\Script.ps1, will read and write a setting:

# get the directory of this script file
$currentDirectory = [IO.Path]::GetDirectoryName($MyInvocation.MyCommand.Path)
# get the full path and file name of the App.config file in the same directory as this script
$appConfigFile = [IO.Path]::Combine($currentDirectory, 'App.config')
# initialize the xml object
$appConfig = New-Object XML
# load the config file as an xml object
$appConfig.Load($appConfigFile)
# iterate over the settings
foreach($connectionString in $appConfig.configuration.connectionStrings.add)
{
    # write the name to the console
    'name: ' + $connectionString.name
    # write the connection string to the console
    'connectionString: ' + $connectionString.connectionString
    # change the connection string
    $connectionString.connectionString = 'Data Source=(local);Initial Catalog=MyDB;Integrated Security=True'
}
# save the updated config file
$appConfig.Save($appConfigFile)

Execute the script:

PS C:\Sample> .\Script.ps1

Output:

name: dbConnectionString  
connectionString: Data Source=(local);Initial Catalog=Northwind;Integrated Security=True

Updated C:\Sample\App.config:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="dbConnectionString" 
      connectionString="Data Source=(local);Initial Catalog=MyDB;Integrated Security=True" />
  </connectionStrings>
</configuration>

Answer 2

The code can be much more shorter (based on Robin's app.config):

$appConfig = [xml](cat D:\temp\App.config)
$appConfig.configuration.connectionStrings.add | foreach {
    $_.connectionString = "your connection string"
}

$appConfig.Save("D:\temp\App.config")