在正则表达式中使用正则表达式替换单词

Question

I am newbie to ansible actually.Can anyone please help me change the ip address in a file using regexp with my original system ip. Let say I wanted to replace "Djgroups.bind_address=<*/WHATEVER/BLANK>" to "Djgroups.bind_address=10.0.0.45"

This would be for a tomcat instance. The Line where the replacement is required:

JAVA_OPTS="-Xms6144m -Xmx6144m -Djava.awt.headless=true -Djava.net.preferIPv4Stack=true -Djgroups.bind_address="

I Wrote ansible as below:

  - name: Verifying Instance IP Address
    shell: grep Djgroups.bind_address /apache-tomcat-8.5.15_1/bin/catalina.sh|grep -v ^#|tr -s '=' '"'|cut -d '"' -f5
    register: tomcat_instance_ip
  - debug: msg='Tomcat instance has {{ tomcat_instance_ip.stdout }} set.'

  - name: Updating Tomcat Instance with valid local IP address
    replace:
      dest: /apache-tomcat-8.5.15_1/bin/catalina.sh
      regexp: '^(Djgroups.bind_address(?!.*\b{{ tomcat_instance_ip.stdout }}\b).*)$'
      replace: '\1 {{ ip_address }}'
    when: tomcat_instance_ip.stdout != ip_address

Thanks, Sam

Answer 1

I see at least 4 issues with the regexp:

1. your . is not escaped, so it is interpreted as a special character.
2. Why do you put ^ at the beginning. Seems like you are trying to find something in the middle of a string, not at the beginning.
3. you should use lazy evaluation for the .* in negative lookup. Right now it will match anything.
4. you are trying to match the Djgroups.bind_address part of the string, while i believe you meant to match whatever comes afterwards instead.

try: Djgroups\\.bind_address=(?!.*?{{ tomcat_instance_ip.stdout }}.*?)(.*)$

And please test your regex first. https://regex101.com/ Make sure it actually matches your input like you imagined.

Answer 2

Remove the shell task, this is not needed.

Try this :

- name: Updating Tomcat Instance with valid local IP address
  replace:
    path: /apache-tomcat-8.5.15_1/bin/catalina.sh
    regexp: 'JAVA_OPTS="(.* )?-Djgroups.bind_address=[^ "]*(.*)"'
    replace: 'JAVA_OPTS="\1-Djgroups.bind_address={{ ip_address }}\2"'

The when is not needed either, since replace module is idempotent.

Edit : some explanations about the regular expression used in this example

'JAVA_OPTS="(.* )?-Djgroups.bind_address=[^ "]*(.*)"'
            ^___^                              ^__^
 ^_________^ (1) ^______________________^       (2)
      (3)                     (4)
                                         ^__^
                                          (5)

• 1 and 2 are the "unknown" parts. This can be anything and we don't want to lose this while applying the replacement. So we capture them with parenthesis. We can re-use them in the replacement by referencing them with \\1 and \\2 .
• 3 and 4 are the "known" parts. They are used to identify the line to be modified. We don't really need to capture them since we actually know their contents.
• 5 is the interesting part, this is what we want to replace with new content. We don't care about its actual content.

Regular expressions are somewhat intimidating at first, with this weird syntax. This not as complicated as it seems. You can find a lot of tutorials to help you understand it.