现在不建议使用setenv。建议使用环境文件。基于@youjin的回答，同时仍然允许功能/分支(用-替换所有/的出现)，我现在使用这个:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Get branch name (merge)
        if: github.event_name != 'pull_request'
        shell: bash
        run: echo "BRANCH_NAME=$(echo ${GITHUB_REF#refs/heads/} | tr / -)" >> $GITHUB_ENV

      - name: Get branch name (pull request)
        if: github.event_name == 'pull_request'
        shell: bash
        run: echo "BRANCH_NAME=$(echo ${GITHUB_HEAD_REF} | tr / -)" >> $GITHUB_ENV

      - name: Debug
        run: echo ${{ env.BRANCH_NAME }}

下面是一个适用于push和pull_request事件的完整工作流

name: whichBranch
on: [pull_request, push]

jobs:
  which_branch:
    runs-on: ubuntu-latest
    steps:
      - name: Extract branch name on push
        if: github.event_name != 'pull_request'
        shell: bash
        run: echo "::set-env name=BRANCH_NAME::$(echo ${GITHUB_REF#refs/heads/})"
        id: extract_branch

      - name: Extract branch name on pull request
        if: github.event_name == 'pull_request'
        run: echo "::set-env name=BRANCH_NAME::$(echo ${GITHUB_HEAD_REF})"

      - name: Print branch name
        run: echo 'The branch name is' $BRANCH_NAME

我做了一个获取分支名称的操作，而不管是否触发pull_request。https://github.com/EthanSK/git-branch-name-action

要处理pull_request事件(在这种情况下，$GITHUB_REF包含一些无用的东西，如refs/pull/519/merge)，你可以使用这一行:

   - name: Set branch name
     run: echo "::set-output name=branch_name::$(echo ${GITHUB_HEAD_REF:-${GITHUB_REF#refs/heads/}})"

${{ github.ref_name }}

至少对推送来说还行。参见ref_name了解更多细节。它说:

触发工作流运行的分支或标记名称。

更新

GitHub现在支持GITHUB_REF_NAME，它代表触发工作流运行的分支或标记名称。

GitHub文档在这个https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables上