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Ubuntu – How to run a workflow on a single matrix element?

The standard way of running a workflow on several operating systems is using a matrix:

jobs:
  package:
    strategy:
      matrix:
        os: [ubuntu, macos, windows]
    runs-on: ${{ matrix.os }}-latest

In some cases, it’s useful to run the workflow on only one of the operating systems, for example, when debugging or when only one of them changed and there’s no need to run the other two. How can only one of them be run?

One solution is to comment out the elements you don’t need, but this is a very local and fragile solution.
Another could be creating 4 different workflows (one for each system + one for all), but this is cumbersome and gets complicated when you have a chain of workflows such as build -> package -> deploy that now needs 4 variants each.

I tried using the choice input to be able to select the systems,

on:
  workflow_dispatch:
    inputs:
      os:
        type: choice
        options:
          - windows
          - macos
          - ubuntu
          - ubuntu, macos, windows
        required: true


jobs:
  package:
    strategy:
      matrix:
        os: "${{ github.event.inputs.os }}"
    runs-on: ${{ matrix.os }}-latest

which works for the single system choice, but not for the multiple one because it’s taken as a single string "ubuntu, macos, windows".

I also tried to use a boolean inputs to select any combination I need:

on:
  workflow_dispatch:
    inputs:
      ubuntu:
        required: true
        type: boolean
      macos:
        required: true
        type: boolean
      windows:
        required: true
        type: boolean

but I’m not sure how to combine them into a matrix. I could do

...
jobs:
  ubuntu:
    if:  ${{ inputs.ubuntu }} 
    runs-on: ubuntu-latest
    steps: ...
  macos:
    if:  ${{ inputs.macos}} 
    runs-on: macos-latest
    steps: ...
  windows:
    if:  ${{ inputs.windows}} 
    runs-on: windows-latest
    steps: ...

Is there a way I’m "supposed" to use to achieve this functionality? Consider also that these workflows can be reusable (run the build -> package -> deploy sequence on a single OS or all), so the OS inputs can be also received from calling workflows.

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    Based on Azeem's answer, I shortened the inputs and matrix handling to omit the "latest" suffix, and added it only in the runs-on key where it is strictly needed. This way ${{ matrix.os }} resolves to just the plain OS name (ubuntu), which can be used elsewhere.

    I also added the reusable workflow workflow_call inputs so the workflow can be called with the same type of input:

    name: package

on:
  workflow_dispatch:
    inputs:
      os:
        description: "Operating System"
        required: true
        type: choice
        options:
          - '["ubuntu", "macos", "windows"]'
          - '["windows"]'
          - '["macos"]'
          - '["ubuntu"]'
  workflow_call:
    inputs:
      os:
        required: true
        type: string

jobs:
  package:
    strategy:
      matrix:
        os: ${{ fromJson(inputs.os) }}
    runs-on: ${{ matrix.os }}-latest
    ...

    name: release

on:
  workflow_dispatch:
    inputs:
      os:
        description: "Operating System"
        required: true
        type: choice
        options:
          - '["ubuntu", "macos", "windows"]'
          - '["windows"]'
          - '["macos"]'
          - '["ubuntu"]'

jobs:
  package:
    uses: ./.github/workflows/package.yml
    with:
      os: ${{ inputs.os }} # pass the expected string format to `package`
  release:
    ...

  2. 0

    To make it work directly without the need of an intermediate job, you can provide options as JSON arrays and then use fromJson function to create matrix like this:

    name: os_matrix_from_inputs

on:
  workflow_dispatch:
    inputs:
      os:
        description: Select OS
        type: choice
        options:
        - '["ubuntu-latest"]'
        - '["windows-latest"]'
        - '["macos-latest"]'
        - '["ubuntu-latest", "macos-latest", "windows-latest"]'
        default: '["ubuntu-latest"]'
        required: true

jobs:
  ci:
    strategy:
      matrix:
        os: ${{ fromJson(inputs.os) }}
    runs-on: ${{ matrix.os }}

    steps:
    - name: Check
      run: echo '${{ matrix.os }}'
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