Change permissions level for the groups in a SharePoint 2010 List or Library

Hi, Recently I needed to breake inherirites for a list on  Sharepoint 2010 site page and change the group permissions to specific one. So here is a powershell script that does the job. You will need to change $OwnerGroupName, $web = Get-SPWeb  $SiteUrl and $list = $web.Lists["<ListName>"]; to your own values.

Task:

Only users in site owner group can have "Full Control"  permissions for specific list on this site. Other groups permissions should be changed to "Read"

What Powershell script does:

1. It breaks inheritance from site
2. Gets all groups on the site
3. Goes via a list role assignments

and

4  If group name is equal to list Role Assignments removes group existing permissions and assign new role with "Read" permissions


Scripts:

[string]$OwnerGroupName = "Owners";

$web = Get-SPWeb  "<SiteUrl>";


$list = $web.Lists["<ListName>"];

$groupCollection =  $web.Groups;

 if ($list -ne $null)
  {
    if (!$list.HasUniqueRoleAssignments)
      {
    $list.BreakRoleInheritance($true);
      }
   $web.AllowUnsafeUpdates = $true;
           foreach ($group in $groupCollection)
{
                Write-Host $group.Name
                if ($group.Name -ne $OwnerGroupName)
                {
                    $roleColl = $list.RoleAssignments
foreach($roleAss in $roleColl){
 
if($roleAss.Member.Name -eq $group.Name){

$permissions = $roleAss.RoleDefinitionBindings
$roleColl.Remove($group)

$roleDef = $web.RoleDefinitions["Read"]
$roleAssign = New-Object Microsoft.SharePoint.SPRoleAssignment($group)
$roleAssign.RoleDefinitionBindings.Add($roleDef)
$list.RoleAssignments.Add($roleAssign)
break
}
}        
    }
}  
$web.AllowUnsafeUpdates = $false;
}