How to Add,Update,Delete List items using powershell sharepoint 2010

A simple example of a powershell script to add items in a SharePoint 2010
list.

$spAssignment = Start-SPAssignment
$mylist = (Get-SPWeb
-identity http://SP -AssignmentCollection
$spAssignment).Lists["listName"]
$newItem = $mylist
.Items.Add()
$newItem["Title"] = "Added by
Powershell"
$newItem["description"] = "My PowerShell
Magic"
$newItem.Update()
Stop-SPAssignment $spAssignment


Update
list item example I -

$SPAssignment = Start-SPAssignment
$SPWeb =
Get-SPWeb http://SP -AssignmentCollection $spAssignment

Next step is to
get the list:
$SPList = $SPWeb.Lists["Announcements"]

When we have
located the list we can retrieve the item. The quickest way is to use the
GetItemByID() method:
$SPItem = $SPList.GetItemById("1")

The example
above requires that you know the ID of the item. If you don't know the items ID
you can use the Where-Object cmdlet instead:

$SPItem = $SPList.Items |
Where { $_["Title"] -eq "New Announcement" }
When you've retrieved the item
you can modify the item information.

$SPItem["Title"] =
"MyTitle"
$SPItem["Body"] = "MyBody"

After modifying an item you have
to call the Update() method to set the changes.
$SPItem.Update()

When
you're done, use the Stop-SPAssignment cmdlet to dispose the SPWeb object.
Stop-SPAssignment $SPAssignment

Delete Item -

The example below
will count the items and loop down, read the name of the item, and if the item
contains a 3, then it will delete that
item.

[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")

$site = new-object Microsoft.SharePoint.SPSite("http://test.tomdaly.com") #
is a legit url
$relweburl = '/Docs"
$web =
$site.openweb($relweburl)
$list=$web.Lists["testList"] $listItems =
$list.Items
$listItemsTotal = $listItems.Count

for
($x=$listItemsTotal-1;$x -ge 0; $x--)
{

if($listItems[$x].name.Contains("3"))
{
Write-Host("DELETED: " +
$listItems[$x].name)
$listItems[$x].Delete()
}
}