Python regexp problem in Ansible playbook

Question

I have a string in Zabbix agent configuration like

HostMetadata=Linux

I want change it with variable "nginx" to:

HostMetadata=Linux nginx

This changes must be idempotent. But when I am using code twice, line changed to

HostMetadata=Linux nginx nginx

My code:

 - name: regexp
 lineinfile:
 path: /etc/zabbix/zabbix_agentd.conf
 regexp: '^(HostMetadata=Linux.*)$'
 line: '1円 nginx'
 backrefs: yes
 tags: regexp

I tried "^HostMetadata=((?!nginx).)*$", but it breaks next step, and result will be "x nginx"

I want create reusable code and add new parameters. For example:

VAR=nginx
"HostMetadata=Linux" -> "HostMetadata=Linux nginx"
VAR=apache
"HostMetadata=Linux nginx" -> "HostMetadata=Linux nginx apache"
VAR=nginx
"HostMetadata=Linux nginx apache" -> "HostMetadata=Linux nginx apache" (nothing changed)

Answer 1

You should only capture the part you need to keep, the rest should be just matched.

You may use

regexp: '^(HostMetadata=Linux).*'

See the regex demo.

Details

• ^ - start of string
• (HostMetadata=Linux) - capturing group #1 (referred to with 1円 from the replacement string): the literal string
• .* - the rest of the string to the end, any 0 or more chars other than line break chars, as many as possible.

• Alxi Rus: Thanks for answer. Sorry, this is my first quiestion =) I added more description to question.
• Wiktor Stribiżew: @AlxiRus So, try ^(HostMetadata=Linux(?!.*nginx).*)
• Wiktor Stribiżew: @AlxiRus Is that better?
• Alxi Rus: Thank you very much! Exactly what I want!