Q:

Create GitHub actions that use powershell scripts

I'd like to create a GitHub action that sets up an environment in Windows, running a few Powershell commands. Despite this can be done easily as a step, there does not seem to be a way to create a complete GitHub action for that. If I use this:
name: 'Rakudo Star fix for windows'
description: 'Updates zef for RakudoStar'
author: 'JJ'
runs:
  using: 'node12'
  main: 'upgrade.ps1'

There does not seem a way to run anything other than a JS script, or even to declare the environment. I understand that's left for later, during the job steps, but anyway it looks like a hack. Is there anything I'm missing here?

A:

You could also run docker directly with an entrypoint for the .ps1 script
FROM ubuntu:18.04

LABEL "com.github.actions.name"="test"
LABEL "com.github.actions.description"="test."

RUN apt-get update \
    && apt-get install wget -y \
    && wget -q https://packages.microsoft.com/config/ubuntu/18.04/packages-microsoft-prod.deb \
    && dpkg -i packages-microsoft-prod.deb \
    && apt-get update \
    && apt-get install -y powershell

ADD test.ps1 /test.ps1
ENTRYPOINT ["pwsh", "/test.ps1"]

Update:
The using field is the application to use to execute the code specified in main. But Github Actions only support using node12 and docker. As seen from this GHActions I just ran for example's sake. 
Docker won't run in most Windows environment and you'd have to use Windows Server 2019 as your base environment.

