Setting Environment Variables From PowerShell Tasks Under TFS 2015

This is less than intuitive, but you can hotwire some underlying functionality to set your own environment variables that will persist from task to task. Here, we take a value from the environment and set another value derived from it.

Write-Host "##vso[task.setvariable variable=ACTIONSFOLDER;]$env:BUILD_DROPFOLDER\Scripts\Steps"