Update Xml via PowerShell

UpdateXml.ps1

function UpdateXml([string]$InputFile = $(Throw "Please provide a path to the input XML file in the InputFile parameter."),
  [string]$OutputFile = $InputFile,
  [string]$ParentXPath = $(Throw "Please provide an XPath expression to where you want to append/edit a child XML element in the ParentXPath parameter."),
  [string]$ElementName = $(Throw "Please provide the name of the XML element to append/edit."),
  [string]$ElementAttributeName,
  [string]$ElementAttributeValue)
{
    if (Test-Path -Path $InputFile)
    {
      Write-Log "Loading XML document from file: $InputFile"
        $Doc = Select-Xml -Path $InputFile -XPath "/"
      if ($Doc -ne $null)
      {
        $UpdatesMade = $False
        $ParentNode = $Doc.Node.SelectSingleNode($ParentXPath)
        if ($ParentNode -ne $null)
        {
          Write-Log "Existing XML elements under '$ParentXPath':"
          $ParentNode.ChildNodes | % { Write-Log "- $($_.Name)" }

          $ExistingElement = $ParentNode.SelectSingleNode("./$ElementName")
          if ($ExistingElement -ne $null)
          {
            if (![System.String]::IsNullOrEmpty($ElementAttributeName))
                    {
                        $ExistingAttribute = $ExistingElement.Attributes.GetNamedItem($ElementAttributeName)
                if ($ExistingAttribute -ne $null)
                {
                  if ($ExistingAttribute.Value -ne $ElementAttributeValue)
                  {
                    $ExistingAttribute.Value = $ElementAttributeValue
                    $UpdatesMade = $true
                    Write-Log "Updated existing XML element '$ElementName' attribute name '$ElementAttributeName' with a new attribute value '$ElementAttributeValue'."
                  }
                  else
                  {
                    Write-Log "Existing XML element '$ElementName' already has correct attribute name '$ElementAttributeName' and value '$ElementAttributeValue'."
                  }
                }
                else
                {
                  $NewAttribute = $Doc.Node.CreateAttribute($ElementAttributeName)
                  $NewAttribute.Value = $ElementAttributeValue
                  $NewAttributeAppened = $ExistingElement.Attributes.Append($NewAttribute)
                  $UpdatesMade = $true
                  Write-Log "Updated existing XML element '$ElementName' with a new attribute name '$ElementAttributeName' and value '$ElementAttributeValue'."
                }
                    }
          }
          else
          {
            $NewElement = $Doc.Node.CreateElement($ElementName)
                    
                    if (![System.String]::IsNullOrEmpty($ElementAttributeName))
                    {
                        $NewAttribute = $Doc.Node.CreateAttribute($ElementAttributeName)
                $NewAttribute.Value = $ElementAttributeValue
                  $NewAttributeAppened = $NewElement.Attributes.Append($NewAttribute)
                  }
            $NewNode = $ParentNode.AppendChild($NewElement)
            $UpdatesMade = $true
            Write-Log "Create a new XML element '$ElementName' with a new attribute name '$ElementAttributeName' and value '$ElementAttributeValue'."
          }

          Write-Log "Current XML elements under '$ParentXPath':"
          $ParentNode.ChildNodes | % { Write-Log "- $($_.Name)" }
        }
        else
        {
          Write-Log "Error: No element found at: $ParentXPath"
        }

        if ($UpdatesMade -or ($InputFile -ne $OutputFile))
        {
          $Doc.Node.Save($OutputFile)
          Write-Log "Saved updated XML to: $OutputFile"
        }
        else
        {
          Write-Log "No updates required to file: $OutputFile"
        }
      }
      else
      {
        Write-Log "Error: Unable to load XML document: $InputFile"
      }
    }
    else
    {
      Write-Log "Error: Input file not found: $InputFile"
    }
}