What is the method to exclusively obtain the PR version from a Git branch in Concourse?

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To exclusively obtain the PR version from a Git branch in Concourse, you can use the following steps:

1. Set up a resource with the Git source and the pull_request property set to true, like this:

   resources:
   - name: pr-source
    type: git
    source:
      uri: git://github.com/your-org/your-repo.git
      branch: master
      pull_request: true
   

2. Use the get step to fetch the latest version of the resource:

   jobs:
   - name: build
    plan:
    - get: pr-source
      trigger: true
    - ...
   

3. Use the metadata output in subsequent steps to get the PR version:

   jobs:
   - name: build
    plan:
    - get: pr-source
      trigger: true
      version: {pr: true}
    - put: output-resource
      params:
        output_file: pr-source/metadata.json
    - ...
   

   You can then parse the metadata output to get the PR version.

   resources:
   - name: output-resource
    type: ...
    source:
      ...
   - name: parse-pr-version
    type:...
    source:
      ...
    check_every: 30s # Or a period long enough to allow the output-resource put to complete.
    tags: [docker]
    inputs:
    - name: output-resource
    outputs:
    - name: pr-version
    run:
      path: sh
      args:
      - -xec
      - |
        # Parse the PR version from the output-resource metadata file
        version=$(jq -er '.version.ref' ${{inputs.output-resource}}/metadata.json | sed 's#refs/pull/##')
        echo "{ \"version\": { \"pr\": \"$version\" } }" > ${{outputs.pr-version}}/version.json