Add/remove sharepoint group using power shell

#Add a sharepoint group using power shell

#Create a sharepoint custom permission using Power shell

$web = get-SPWeb "http://sitecollectionName"
$member = $web.AllUsers["domain\username"]
$CustomPermission ="Permission Name"
$CustomRoleRoledef = New-Object "Microsoft.SharePoint.SPRoleDefinition"
$CustomRoleRoledef.Name = "$CustomPermission"
$CustomRoleRoledef.Description = "Custom permission level for Site Owners"
$CustomRoleRoledef.BasePermissions =
"CancelCheckout,AddListItems,EditListItems,DeleteListItems,ViewListItems,OpenItems,ViewVersions,DeleteVersions,CreateAlerts,ViewFormPages,ViewUsageData,ViewPages,BrowseUserInfo,ManageAlerts,UseRemoteAPIs,UseClientIntegration,Open"
$web.RoleDefinitions.Add($CustomRoleRoledef)
$web.Update()

# Create custom group
$CustomGroup ="My Custom Group"
$web.SiteGroups.Add("$CustomGroup", $member, $null,"Custom Group ")

#Assign Permission to the Group
$customPermission = $web.RoleDefinitions["$CustomRoleRoledef "]
# If you don't want to use custom permission, you can directly give existing permission name i.e "Full Control/Contributor/Design/Visitor"
#$existingPermission = $web.RoleDefinitions["Design"]
$customPermissionAssignment = New-Object "Microsoft.SharePoint.SPRoleAssignment" -ArgumentList $web.SiteGroups["$CustomGroup"]
$customPermissionAssignment.RoleDefinitionBindings.Add($customPermission)
$web.RoleAssignments.Add($techAdminRoleAssignment)


#Remove a sharepoint group using power shell

#Remove Groups if already exist
$GroupName ="Custom Group"
$objSiteGroup = $web.SiteGroups["$GroupName"]
if ($objSiteGroup)
{
$web.SiteGroups.Remove("$GroupName")
}


Note: you can save above script in .ps1 extension file and execute in power shell