Github Action在Docker镜像中不识别[[...]]语句的解决求助

问题背景 #

我有一个GitHub Action，用于PR从release/**分支合并到master时自动递增RC版本号并提交回release分支。为避免触发无限循环，我添加了如下检查步骤：

- name: Check if version number has changed
        run: |
          if [[ $(git show HEAD | grep -e "\"version\":.*-rc\..*") ]]; then
            echo "Version number has changed, moving onto next jobs"
            exit 1
          else
            echo "Version number has not changed, continuing with this job"
          fi

运行时却报错：

1: [[: not found
Version number has not changed, continuing with this job

这个错误导致检查逻辑失效，触发了无限循环。我试过切换到ubuntu:latest镜像、在脚本开头加#!/bin/bash，都没用，而本地WSL Ubuntu环境中这个语句能正常运行。

问题原因 #

GitHub Action的run步骤默认使用sh（Ubuntu镜像中是dash）而非bash，[[是bash专属的扩展语法，sh不支持，因此会报错，进而导致分支判断走了else分支，触发后续版本递增逻辑，形成循环。

修复方案 #

方案1：改用POSIX兼容的[语法 #

把[[ ... ]]替换为[ ... ]，同时用-n检查输出是否非空：

- name: Check if version number has changed
        run: |
          if [ -n "$(git show HEAD | grep -e "\"version\":.*-rc\..*")" ]; then
            echo "Version number has changed, moving onto next jobs"
            exit 1
          else
            echo "Version number has not changed, continuing with this job"
          fi

方案2：强制使用bash执行 #

在步骤中明确指定用bash运行脚本，有两种方式：

方式A：设置shell字段为bash

- name: Check if version number has changed
        shell: bash
        run: |
          if [[ $(git show HEAD | grep -e "\"version\":.*-rc\..*") ]]; then
            echo "Version number has changed, moving onto next jobs"
            exit 1
          else
            echo "Version number has not changed, continuing with this job"
          fi

方式B：通过bash -c调用

- name: Check if version number has changed
        run: bash -c 'if [[ $(git show HEAD | grep -e "\"version\":.*-rc\..*") ]]; then echo "Version number has changed, moving onto next jobs"; exit 1; else echo "Version number has not changed, continuing with this job"; fi'

优化版检查逻辑 #

可以直接利用grep的退出码判断，无需捕获输出，更高效：

- name: Check if version number has changed
        shell: bash
        run: |
          if git show HEAD | grep -q -e "\"version\":.*-rc\..*"; then
            echo "Version number has changed, moving onto next jobs"
            exit 1
          else
            echo "Version number has not changed, continuing with this job"
          fi

-q参数让grep静默运行，找到匹配时返回0，未找到返回1，直接用于if判断即可。

内容的提问来源于stack exchange，提问作者Alistair Hardy