Editing Web Config file using Microsoft PowerShell - c#-4.0

Question

i want to modify my web config file using powershell . i stuck in somewhere . i want to update appsettings and also connectionsstring information at the same time when i change them in powershel
I have this code but it changes only apppsettings value when i change it here and run it but i also want to include connectionstring here. How can i achieve it ?
$webConfig = "C:\Inetpub\Wwwroot\application\web.config"
$doc = new-object System.Xml.XmlDocument
$doc.Load($webConfig)
$doc.get_DocumentElement()."appsetting".add[0].value = "true"
$doc.Save($webConfig)
Here is my web config file
<appSettings>
<add key="mykey1" value="false"/>
<add key="mykey2" value="true"/>
<add key="mykey3" value="false"/>
</appSettings>
<connectionstrings>
<add name="myname1" connectinstring="Data Source=ABDULLAH-PC\SQLEXPRESS;Initial Catalog=UserDataBase;
Integrated Security=True" providerName="System.Data.SqlClient" />
<add name="myname2" connectinstring="myconnectionstring2" />
<add name="myname3" connectinstring="myconnectionstring3" />
</connectionStrings>
Here i want to upadate appsettings -( key and value) and also connectionstrings( name and initialcatalog)
at the same time
when i tried your code it gives me this error
Property '#text' cannot be found on this object; make sure it exists and is settable.
At line:3 char:66
+ $doc.SelectSingleNode('//appSettings/add[#key="mykey1"]/#value'). <<<< '#text' = 'false'
+ CategoryInfo : InvalidOperation: (#text:String) [], RuntimeException
+ FullyQualifiedErrorId : PropertyNotFound
Property '#text' cannot be found on this object; make sure it exists and is settable.
At line:4 char:85
+ $doc.SelectSingleNode('//connectionStrings/add[#name="myname1"]/#connectionstring'). <<<< '#text'='my_string'
+ CategoryInfo : InvalidOperation: (#text:String) [], RuntimeException
+ FullyQualifiedErrorId : PropertyNotFound

Answer 1

$webConfig = "C:\Inetpub\Wwwroot\application\web.config"
$doc = (gc $webConfig) -as [xml]
$doc.SelectSingleNode('//appSettings/add[#key="mykey1"]/#value').'#text' = 'true'
$doc.SelectSingleNode('//connectionStrings/add[#name="myname1"]/#connectionstring').'#text' = 'my_string'
$doc.Save($webConfig)
You can use XPath to select your nodes and set their value via the #text property PowerShell adds.
Note - your example xml has problems with casing and some typos. Here is what I tested with:
<root>
<appSettings>
<add key="mykey1" value="false"/>
</appSettings>
<connectionStrings>
<add name="myname1" connectionstring="Data Source=ABDULLAH-PC\SQLEXPRESS;Initial Catalog=UserDataBase; Integrated Security=True" providerName="System.Data.SqlClient" />
</connectionStrings>
</root>