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

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 }}

我相信GITHUB_REF是唯一包含分支名称的环境变量。

你可以从字符串的其余部分提取分支名称，如下所示:

${GITHUB_REF##*/}

例子:

$ GITHUB_REF=refs/heads/feature-branch-1
$ echo ${GITHUB_REF##*/}
feature-branch-1

更新:添加了一个完整的工作流示例。

工作流

name: CI
on: push
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Git checkout
        uses: actions/checkout@v1
      - name: Branch name
        run: echo running on branch ${GITHUB_REF##*/}
      - name: Build
        run: docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .

来源:https://github.com/tedmiston/x/blob/master/.github/workflows/workflow.yml

示例输出-主分支

Run docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .
  docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .
  shell: /bin/bash -e {0}
Sending build context to Docker daemon  146.9kB

Step 1/1 : FROM alpine
latest: Pulling from library/alpine
9d48c3bd43c5: Pulling fs layer
9d48c3bd43c5: Verifying Checksum
9d48c3bd43c5: Download complete
9d48c3bd43c5: Pull complete
Digest: sha256:72c42ed48c3a2db31b7dafe17d275b634664a708d901ec9fd57b1529280f01fb
Status: Downloaded newer image for alpine:latest
 ---> 961769676411
Successfully built 961769676411
Successfully tagged tedmiston/tag-example:master

日志:https://github.com/tedmiston/x/commit/cdcc58a908e41d3d90c39ab3bf6fef1ad2c4238a/checks一步:16

示例输出-非主分支

Run docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .
  docker build -t tedmiston/tag-example:${GITHUB_REF##*/} .
  shell: /bin/bash -e {0}
Sending build context to Docker daemon  144.9kB

Step 1/1 : FROM alpine
latest: Pulling from library/alpine
9d48c3bd43c5: Pulling fs layer
9d48c3bd43c5: Verifying Checksum
9d48c3bd43c5: Download complete
9d48c3bd43c5: Pull complete
Digest: sha256:72c42ed48c3a2db31b7dafe17d275b634664a708d901ec9fd57b1529280f01fb
Status: Downloaded newer image for alpine:latest
 ---> 961769676411
Successfully built 961769676411
Successfully tagged tedmiston/tag-example:branch-name-test

日志:https://github.com/tedmiston/x/commit/4e8d31259f861aaa2c30375756fc081c3659bddf/checks一步:16

有关参数展开语法的更多信息，请参阅这个答案。

作为参考，GitHub Actions的虚拟环境页面列出了执行环境中可用的所有环境变量。

有一个非常简单的git命令来获取当前分支:

git rev-parse --abbrev-ref HEAD

要在env文件变量中获得输出，只需输入:

      - name: Set CURRENT_BRANCH
        run: echo "CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)" >> $GITHUB_ENV

获取env变量的输出:

      - name: Get CURRENT_BRANCH
        run: echo ${{ env.CURRENT_BRANCH}}

来源:https://www.techiedelight.com/determine-current-branch-name-git/

我只是在GitHub Actions中使用bash脚本做了一个简单的测试:

#!/bin/bash

echo Reserved for REPO_NAME=${GITHUB_REPOSITORY##*/}
echo GITHUB_REF=${GITHUB_REF}
echo EXTRACT_GITHUB_REF=${GITHUB_REF##*/}
echo EXTRACT_GITHUB_REF_HEADS=$(echo ${GITHUB_REF#refs/heads/})

cd $REPO_NAME
git checkout ${GITHUB_REF##*/}
git checkout $(echo ${GITHUB_REF#refs/heads/})

以下是输出的截图:

因此${GITHUB_REF##*/}和$(echo ${GITHUB_REF#refs/heads/})都是正确的

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