如何在Ansible中正确使用变量存储的shell输出执行后续任务

需求 #

• 将代码仓库克隆到远程节点
• 使用grep从git仓库内的文本文件中提取包列表
• 将包列表加载到Ansible变量并通过apt/package模块安装

现有Playbook #

---
- hosts: all
  become: true
  vars:
    username: foobar

  tasks:
    - name: Install git package
      package:
        name: git
        state: present

    - name: Clone GIT Repo
      git:
        repo: https://github.com/somerepo/.dotfiles.git
        dest: /home/{{ username }}/.dotfiles
        clone: yes
        version: master
        update: yes
        force: yes

    - name: Set permission on folder ~/.dotfiles
      file:
        dest: /home/{{ username }}/.dotfiles
        recurse: yes
        owner: "{{ username }}"
        group: "{{ username }}"
        mode: "0775"

    - name: Extract list of needed tools from install.sh
      shell:
        cmd: grep "^tools=" /home/{{ username }}/.dotfiles/install.sh | tr '"' " " | cut -c7-
      register: grep_output

    - name: Install following packages "{{ grep_output }}"
      apt:
        name: "{{ grep_output }}"
        state: present
        update_cache: yes

提取包的Shell命令及输出 #

用于提取包列表的命令：

grep "^tools=" install.sh |tr '"' " " |  cut -c7-

命令标准输出：

zsh neovim vim tmux ranger stow wget curl git fzf

错误信息 #

执行Playbook时触发如下错误：

PLAY [all] *******************************************************************************************************************

TASK [Gathering Facts] *******************************************************************************************************
[WARNING]: Platform linux on host vm-mint21 is using the discovered Python interpreter at /usr/bin/python3.10, but future
installation of another Python interpreter could change the meaning of that path. See https://docs.ansible.com/ansible-core/2.12/reference_appendices/interpreter_discovery.html for more information.
ok: [vm-mint21]

TASK [Install git package] ***************************************************************************************************
ok: [vm-mint21]

TASK [Clone GIT Repo] ********************************************************************************************************
changed: [vm-mint21]

TASK [Set permission on folder ~/.dotfiles] **********************************************************************************
changed: [vm-mint21]

TASK [Extract list of needed tools from install.sh] **************************************************************************
changed: [vm-mint21]

TASK [Install following packages "{'changed': True, 'stdout': ' zsh neovim vim tmux ranger stow wget curl git fzf ', 'stderr': '', 'rc': 0, 'cmd': 'grep "^tools=" /home/soeren/.dotfiles/install.sh | tr \'"\' " " | cut -c7-', 'start': '2022-09-12 22:33:37.056914', 'end': '2022-09-12 22:33:37.061264', 'delta': '0:00:00.004350', 'msg': '', 'stdout_lines': [' zsh neovim vim tmux ranger stow wget curl git fzf '], 'stderr_lines': [], 'failed': False}"] ***
fatal: [vm-mint21]: FAILED! => {"changed": false, "msg": "argument 'package' is of type <class 'dict'> and we were unable to convert to list: <class 'dict'> cannot be converted to a list"}

PLAY RECAP *******************************************************************************************************************
vm-mint21                  : ok=5    changed=3    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0

核心错误提示（已翻译）：

参数'package'是字典类型，无法转换为列表：字典不能转为列表

问题原因 #

register: grep_output会将整个shell任务的返回结果（包含stdout、stderr、rc等字段的字典）存入变量，而你直接将这个字典传给了apt模块的name参数——该参数需要的是包名列表，而非字典，因此触发类型转换错误。

解决方案 #

方案1：直接使用stdout并转换为列表 #

修改安装任务，通过grep_output.stdout获取命令的标准输出，再用split()将空格分隔的字符串转为列表：

- name: Install required packages
  apt:
    name: "{{ grep_output.stdout.split() }}"
    state: present
    update_cache: yes

方案2：用Ansible原生模块替代Shell（推荐） #

避免依赖shell命令，改用slurp读取文件内容，结合正则表达式提取包列表，更符合Ansible最佳实践：

# 替换原有的shell提取任务
- name: Read install.sh content
  slurp:
    path: /home/{{ username }}/.dotfiles/install.sh
  register: install_sh_content

- name: Extract tools list into variable
  set_fact:
    tools_list: "{{ (install_sh_content.content | b64decode) | regex_search('^tools=\"(.*)\"', '\\1') | first | split() }}"

- name: Install required packages
  apt:
    name: "{{ tools_list }}"
    state: present
    update_cache: yes

内容的提问来源于stack exchange，提问作者edinazzu