title: try to modify a item filed in sharepoint using powershell
body: <p>this is some code I wrote:</p>
  
  <pre><code>Add-PSSnapin Microsoft.SharePoint.PowerShell
  
  $webURL = "http://nycs00058260/sites/usitp"
  $lists = "OsEM1","OsEM2","OsEM3","OsEM4"
  $web = Get-SPWeb -Identity "http://nycs00058260/sites/usitp"
  foreach($list in $lists)
     ... ...
     Write-Host $item["Title"]
     #$item["Item"]=$item["Title"] +" ,"+$webURL+"\"+$filename
     $item["Item"]="$tmpValue"+" ,$item[Title]"   
     $item.Update()
    }
  }
  }
  </code></pre>
  
  <p>it said: Unable to index into an object of type MicroSoft.SharePoint.SPListItem.
  something worong when I change the $item["Item"] value?</p>