How to change values of web.config file using powershell

Question

Hi I am trying to change the values of a connection string for a web.config file but getting error:

The property 'connectionString' cannot be found on this object. Verify that the property exists and can be set.

Here's the script I'm using:

$webConfig = 'C:\Users\test\Desktop\web\web.config'
$doc = (Get-Content $webConfig) -as [Xml]
$obj = $doc.configuration.appSettings.add | where {$_.Key -eq 'CommandTimeOut'}
$obj.value = '60'
$config = [xml](gc $webConfig)  
$con= $config.configuration.connectionStrings.add|where-object{$_.name -eq "password"};

$con.connectionString = $con.connectionString -replace "123456", "admin1234"

$doc.Save($webConfig)

I've modified the code as below, but it's still not working and I'm getting the same error.

$cfg = [xml](gc $webConfig) 
$con= $cfg.configuration.connectionStrings.add|where-object{$_.name -eq "password"};
$cfg.configuration.connectionStrings.add.connectionString=   
$cfg.configuration.connectionStrings.add.connectionString -replace "123456","admin123"
$doc.Save($webConfig)

Answer 1

Late, but just in case someone may find a use for it, I've written a re-usable Power-Shell do to that.

    #set the value of this to your own db config
$myConnectionString = "Data Source=.;Initial Catalog=<Database>;Integrated Security=True";

$webConfig = '.\Api\Web.config'
$dbUpConfig = '.\Database\App.config'
$unitTestConfig = '.\Test\App.config'

Function updateConfig($config) 
{ 
$doc = (Get-Content $config) -as [Xml]
$root = $doc.get_DocumentElement();
$activeConnection = $root.connectionStrings.SelectNodes("add");
$activeConnection.SetAttribute("connectionString", $myConnectionString);
$doc.Save($config)
} 

updateConfig($webConfig)
updateConfig($dbUpConfig)
updateConfig($unitTestConfig)

Answer 2

a dirty way could be to replace the text without parsing the xml, something like this (in case there is no previous connectionstrings defined ) :

$replacementstring=@"
<connectionStrings>
  <add 
    name="NorthwindConnectionString" 
    connectionString="Data Source=serverName;Initial 
    Catalog=Northwind;Persist Security Info=True;User 
    ID=userName;Password=password"
    providerName="System.Data.SqlClient"
  />
</connectionStrings>
"@

(gc c:\temp\web.config) -replace "<connectionStrings/>" ,$repl  | out-file c:\temp\new_web.config