How can I use regex in when condition

Question

On an Ansible playbook, I'm trying to execute a shell command only if a service exist on the remote server.

I have 3 tasks :

• service_facts
• execution of shell command if tomcat is installed
• display the output of the shell command if tomcat is installed

Here is my code :

- name: Get Infos
 hosts: all
 gather_facts: yes
 become: false
 remote_user: [MY_USER]
 tasks:
 - name: Get the list of services
 service_facts:
 - name: Get version of Tomcat if installed
 become: true
 shell: 'java -cp /opt/tomcat/lib/catalina.jar org.apache.catalina.util.ServerInfo | grep "Server version"'
 register: tomcat_version
 when: "'tomcat.service' in services"
 - debug: msg="{{ tomcat_version.stdout_lines }}"
 when: "'tomcat.service' in services"

The problem is on certains servers the service name is, for example, tomcat-8.1

How can i use regex in the when condition?

I tried regex(), regex_search(), either I'm doing it wrong or I don't know how to do it.

Have you any idea how to do it?

Thanks in advance!

Answer 1

Count matching items. For example

 - service_facts:
 - block:
 - shell: smartctl --version | head -1
 register: smart_version
 - debug:
 msg: "{{ smart_version.stdout_lines }}"
 when: _srvcs|length > 0
 vars:
 _regex: '.*smart.*'
 _srvcs: "{{ services|select('match', _regex) }}"

gives

 msg:
 - smartctl 7.1 2019年12月30日 r5022 [x86_64-linux-5.4.0-73-generic] (local build)

---

The next option is to intersect the list of services, e.g.

 when: _srvcs|length > 0
 vars:
 my_services:
 - smartmontools.service
 - smart-8.1
 - smart-devel.0.0.1
 _srvcs: "{{ my_services|intersect(services) }}"

---

Debug

Q: "It gives me a failure on the server where my service doesn't exist, cause the playbook still tries to execute the shell. Is it normal?"

A: No. It is not normal. Print debug and find out why the condition evaluates to true, i.e. what service(s) match either the regex or the list. For example

 - debug:
 msg: |
 _srvcs:
 {{ _srvcs|to_nice_yaml|indent(2) }}
 when: debug|d(false)|bool
 vars:
 my_services:
 - smartmontools.service
 - smart-8.1
 - smart-devel.0.0.1
 _srvcs: "{{ my_services|intersect(services) }}"

gives

 msg: |-
 _srvcs:
 - smartmontools.service

To enable the task run the playbook with the option -e debug=true.

• Quentin Rey: Thanks for your reply! With count matching items, it works, but it give me a failed on server where my service doesn't exist, cause the playbook still try to execute the shell. Is it normal?
• Vladimir Botka: You are welcome! Debug the task. I updated the answer. Then edit question and add the minimal reproducible example details for others to learn what was going wrong.