Get all the columns for the specified SharePoint 2010 site using web service in powershell

 
## Get all the site columns using SharePoint 2010 web service in powershell 
$uri="http://serverName:10736/sites/ECT/_vti_bin/Webs.asmx?wsdl" 
## Web Service Reference - http://Site/_vti_bin/Webs.asmx
$websWebServiceReference = New-WebServiceProxy -Uri $uri -UseDefaultCredential

[System.Xml.XmlNode]$xmlNode=$websWebServiceReference.GetColumns()
## Creates an Columns.xml file in the D:\ which contains column definitions for the columns available on the site
$output = New-Object -TypeName System.IO.StreamWriter -ArgumentList "D:\Columns.xml", $false
$output.WriteLine("<?xml version=""1.0"" encoding=""utf-8"" ?>")
$output.WriteLine($xmlNode.OuterXml)
$output.WriteLine()
$output.Dispose()
Write-Host -ForegroundColor Magenta "Getting all site Columns................"
foreach($node in $xmlNode.Field)
{
Write-Host -ForegroundColor Green $node.Name 
}