I first discussed GPMC in tip 6494 ยป Introducing the Group Policy Management Console.

The Group Policy Management Console Scripting Samples page contains:

The following is a description of the Group Policy Management Console (GPMC) scripting samples. You can find the samples in the %programfiles%\gpmc\scripts directory after you install the GPMC. The scripts can be executed from the command line. The scripts echo output to the command window and should be executed using the CScript.exe application.

The following script samples address administrative tasks:

Backing up an Individual GPO
Backing up the GPOs in a Domain
Creating a Copy of a GPO
Creating a New GPO
Creating a Policy Environment Using an XML File
Creating an XML File that Represents a Policy Environment
Create Migration Table
Deleting a GPO
Grant Permissions for all GPOs in a Domain
Importing a GPO
Importing Multiple GPOs into a Domain
Restoring a GPO
Restoring All GPOs in a Domain
Setting GPO Permissions
Setting Permissions for all GPOs Linked to a Scope of Management
Setting Permissions to Create GPOs
Setting Policy-related Permissions on a SOM

There are also script samples that perform the following queries:

Listing All GPOs in a Domain
Listing Disabled GPOs
Listing GPO Information
Listing GPOs at a Backup Location
Listing GPOs by Policy Extension
Listing GPOs by Security Group
Listing GPOs Orphaned in SYSVOL
Listing GPOs With Duplicate Names
Listing GPOs Without Security Filtering
Listing SOM Information
Listing SOMs With Links to GPOs in External Domains
Listing Unlinked GPOs in a Domain
Printing the SOM Policy Tree
Generate Reports for all GPOs
Generate Reports for a GPO