That is perfect. Thank you Owen.

Just one more thing, as it is related:
does do_not_increment_build_number: true work with this as well?

I have this config:

  version: 0.1.{build}

  environment:
      PSGalleryAPIKey:
          secure: xxxxx
      access_token:
          secure: xxxxx
      matrix:
          - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
          # waiting on https://github.com/RamblingCookieMonster/BuildHelpers/pull/60
          # - APPVEYOR_BUILD_WORKER_IMAGE: WMF 4
          - APPVEYOR_BUILD_WORKER_IMAGE: Ubuntu
            PowershellVersion: "6.0.0"
          - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
            PowershellVersion: "6.0.0"

  # Fail the Build with the first Job that failes
  matrix:
      fast_finish: true
  # Don't rebuild when a release is tagged on GitHub
  skip_tags: true
  # Do not increase AppVeyor's build number
  do_not_increment_build_number: true
  # Logic for skipping CI is in the build script

  for:
  -
      branches:
          only:
              - master
      do_not_increment_build_number: false

  init:
      - ps: |
          if (-not ($env:PowershellVersion)) {$env:PowershellVersion = "5.1"}
          if (([version]$env:PowershellVersion).Major -ge 6) {$env:posh = "pwsh"} else {$env:posh = "powershell"}
          Add-Content (Join-Path $Home ".git-credentials") "https://$($env:access_token):x-oauth-basic@github.com`n"
      - git config --global credential.helper "store --file ~/.git-credentials"
      - git config --global user.email "[email blocked]"
      - git config --global user.name "AtlassianPS automation"

  install:
      - ps: '& $env:posh -File "./Tools/setup.ps1"'

  build_script:
      - ps: '& $env:posh -Command "Invoke-Build"'

  # on_failure:
      # - ps: $blockRdp = $true; iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-rdp.ps1'))

I get the following error

Error parsing appveyor.yml: Invalid setting or section: do_not_increment_build_number (Line: 29, Column: 5) on line

  do_not_increment_build_number: true

and if I comment that out, I get the same error on:

  for:
  -
      branches:
          only:
              - master
      do_not_increment_build_number: false

Thank you, Owen - that works. But is not what I am trying to do.

This will only have Pull Request to have a random hash appended to the version, so that the build number is not increased.
I want all commits of all branches to behave like that. With the exception of the master branch - master should increase the build number

We created this workaround for you. It is a kind of hack but should work.

I really appreciate this, Owen & Ilya.
I will use that.

Is this something AppVeyor would like to support as a feature?
Should I create a github issue asking for this feature (as a non-workaround)?

Sure, feel free to add GitHub issue. However we need to see how many people will vote for it.

Alternative solution by the way: use separate AppVeyor project for master and separate for other branches.

oh! I like this better. Thanks!

Hey, Ilya...
This setup didn't quite work out as I hoped.
I would appreciate it, if you could take a look and point out where my mistake is.

location of appveyor.yml: <projectroot>/Tools/appveyor.yml
config in the UI: screenshot: vivaldi_2018-08-05_22-21-29.png

config in the UI for the branches:
AppVeyor project AtlassianPS.Configuration: vivaldi_2018-08-05_22-22-52.png
AppVeyor project AtlassianPS.Configuration@next: vivaldi_2018-08-05_22-23-34.png

and this commit triggered both to run the CI:
* https://ci.appveyor.com/project/AtlassianPS/atlassianps-configurati... * https://ci.appveyor.com/project/AtlassianPS/atlassianps-configurati...

So I would have to have 2 different appveyor.yml files with exactly the same content except for the branches: block?

great! thanks