How to get SharePoint workflow inventory details using PowerShell.

Hi,

We have a SharePoint farm where multiple web application is running and in each web application has thousands of sites and sub sites where multiple workflow is running. So I want to get an inventory using PowerShell script using which I will get the details about all workflows in the farm. This script I will run periodically - so is there any script available which we can use with little customization? Thanks in advance.

Thanks,

Ashish