Easy object disposal in SharePoint 2010 PowerShell scripts

If you’ve done any type of SharePoint development, you’ll know about SPSite and SPWeb object disposal (see here if not). I’m not going to cover the subject again, except to say that you also need to build in disposal practices when using PowerShell scripts for SharePoint to avoid retaining the objects in memory, potentially causing performance issues on your servers.

PowerShell will automatically dispose of objects used in certain types of commands - e.g., those that appear on a single line or as part of a piped command, but you will need to manually dispose of objects for commands where you are instantiating a variable using Get-SPSite or Get-SPWeb. For example, PowerShell will automatically handle object disposal for the following command:

Get-SPWebApplication | Get-SPSite -limit all | ForEach-Object { write-host $_.Url  }

But, as the command below creates a variable called $web based on the SPWeb object, this will require disposal by specifying the $web.dispose() command after it has been used:

$web = Get-SPWeb http://portal
#PowerShell script goes here
#Now dispose of SPWeb object
$web.dispose()

Now, for all you IT Pro’s out there, this alone may scare you into never using PowerShell to manage SharePoint again (and I wouldn’t blame you). However, help is at hand with the Start-SPAssignment and Stop-SPAssignment cmdlets introduced in SharePoint 2010. To overcome the hassle of having to know when to dispose of an object and when not to, all you need to do is sandwich your script in between the following commands:

Start-SPAssignment –Global

#PowerShell script goes here

Stop-SPAssignment –Global

Any objects defined between the Start-SPAssignment –Global and Stop-SPAssignment –Global commands will be automatically disposed of by PowerShell as it will now know when the script has finished running. So, even if you are not sure whether objects should be disposed of or not, as long as you always top and tail your script with these cmdlets, you can’t go wrong.