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## This script searches for all Web Applications using a specific application pool 'Old Application Pool' and updates it's property in SharePoint configuration to use a 'New Application Pool' 
## USAGE: 
## REQUIREMENT: Ensure the new application pool to be used is already registered in SharePoint. This happens when you create a new Web Application with a new Application pool. 
## SYNTAX:      ChangeApplicationPool <old application pool name> <new application pool name>" 
## NOTE:        Application pool name is case sensitive. 
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# Define 2 parameters for this script 
param([string] $oldAPName, [string] $newAPName) 

# Check if both params are passed, else show Syntax. 
if ($newAPName -eq "") 
{ 
   "Syntax: ChangeApplicationPool <old application pool name> <new application pool name>" 
   exit; 
} 

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

$WebService = [Microsoft.SharePoint.Administration.SPWebService]::ContentService 

## Get reference for the new application pool within the list of SharePoint objects 
[Microsoft.SharePoint.Administration.SPApplicationPoolCollection] $appPools = $webService.ApplicationPools; 
$newAppPool = $NULL; 
foreach ($appPool in $appPools) 
{ 
    if ($appPool.Name -eq $newAPName) 
    { 
        [Microsoft.SharePoint.Administration.SPApplicationPool]$newAppPool = $appPool; 
    } 
} 

## If new application pool is not found, then give error and exit 
if($newAppPool -eq $NULL) 
{ 
    "ERROR: The New application pool to be assigned was not found within SharePoint!" 
    "REQUIREMENT: Ensure the new application pool to be used is already registered in SharePoint. This happens when you create a new Web Application with a new Application pool." 
    exit; 
} 

## Now loop through all Web Applications to find a match of the old Application pool and update it with New App pool. 
[Microsoft.SharePoint.Administration.SPWebApplicationCollection] $webApps = $webService.WebApplications 

"Searching through all Web Applications for Old Application pool - " + $oldAPName + " and changing it to - " + $newAPName 
$count=0; 
foreach ($webApp in $webApps) 
{ 
    $webApp.DisplayName + " uses application pool " + $webApp.ApplicationPool.Name 
    if($webApp.ApplicationPool.Name -eq $oldAPName) 
    { 
        $webApp.ApplicationPool = $newAppPool;   ## Changed to new Application pool reference. 
        $webApp.Update(); 
        $webApp.ProvisionGlobally(); 
        "............" + $webApp.DisplayName + " now uses the new application pool " + $webApp.ApplicationPool.Name 
        $count = $count + 1; 
    } 
} 
"Found and replaced " + $count + " web application(s)" 

if($count -eq 0) 
{ 
   "Syntax: ChangeApplicationPool <old application pool name> <new application pool name>" 
   "Ensure the application pool name is an exact match" 
} 

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