how to provide a parameter to s powershell script in userdata

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I tried to launch a windows stack using heat template. the userdata is powershell script created by myself . I tried: setupenv.ps1 -specificurl "http://...." setupenv.ps1 "http://....." but neither works my script is like: param([String]specificurl) (new-object System.Net.WebClient).DownloadFile($specificurl,"C:\temp")

Could you pls tell me how to pass the parameter to the script in userdata?

Thanks a lot