Create a new branch only if one doesn't already exist

create_or_checkout.yml

name: Create or Update Branch
on:
  workflow_dispatch:
    inputs:
      branch:
        required: true

jobs:
  checkout-branch:
    runs-on: ubuntu-latest
    steps:
      - name: Initial Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0 # fetch depth 0 means "pull the whole thing"
          token: ${{ secrets.GH_PAT }}

      - name: Checkout Branch and Perform Initial Config Setup
        env:
          BRANCH: ${{ inputs.branch }}
        run: |
          git config --global user.email "[email protected]"
          git config --global user.name "Robot"
          git config pull.ff only
          git fetch # just in case?

          # try to checkout an existing branch first
          # (and use this as a starting point when creating the new branch below)
          # if we don't find a branch here, this will just create our new branch from the trunk
          if git checkout "origin/$BRANCH" ; then
            git pull origin "$BRANCH"
          fi

          git checkout -B "$BRANCH" # create a "new" branch

      - name: Modify some files
        run: echo "test" >> ./test

      - name: Push the changes
        env:
          BRANCH: ${{ inputs.branch }}
        run: |
          git add .
          git commit -m 'test'
          git push origin "$BRANCH"