One of the central building blocks of Ansible is adaptability and the set of features for various environments. This is true even in operations such as string manipulation which can be challenging when dealing with multiple files or hosts.
This tutorial explores the robust set of filters available in the Ansible ecosystem to manipulate the data within the templates and playbooks.
We will, of course, talkabout the regex_replace filter module. This powerful tool allows us to apply the regular expression operations on string values, providing extensive and very powerful pattern matching and replacement.
Ansible Regexp_Replace: Syntax and Usage
Before we dive into the depths, let’s understand the basic syntax of this feature:
We can express the given syntax as follows:
original_string – The string on which you want to apply the regex.
pattern_to_match – The regex pattern to look for within the original string.
replacement_string – The string that replaces the matched pattern.
Example 1: Basic Usage
Let us look at a basic example of using this feature.
Suppose we have a string that says “Port to MySQL is 3306” and we wish to replace the “MySQL” string with “MariaDB”.
Example 2: Replacing the IP Addresses
Suppose we aim to find the IP addresses and replace them within the logs to ensure the user privacy. We can create a playbook that does this for us as demonstrated in the following example:
- hosts: localhost
vars:
log_message: "User logged in from 192.168.1.1"
tasks:
- name: Mask IP Address
debug:
msg: "{{ log_message | regex_replace('(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3})', 'XXX.XXX.XXX.XXX') }}"
The previous playbook should locate the IP address of the user and replace it with the defined values as follows:
ok: [localhost] => {
"msg": "User logged in from XXX.XXX.XXX.XXX"
}
Example 3: Masking the Email Addresses
We can also use the regex_replace feature to create a regular expression that replaces the email addresses with the masked values. An example playbook demonstration is as follows:
- hosts: localhost
vars:
email_string: "Contact me at [email protected]"
tasks:
- name: Mask Email Address
debug:
msg: "{{ email_string | regex_replace('([a-zA-Z0-9._%+-]+)@', 'XXXX@') }}"
Similarly, the previous playbook should return a masked value as follows:
Example 4: Removing the HTML Tags
Consider another example where we need to extract a plain text from a string of the HTML data. We can make use of regular expressions as demonstrated in the following:
- hosts: localhost
vars:
html_content: "<p>Greetings from Linuxhint!</p>"
tasks:
- name: Strip HTML tags
debug:
msg: "{{ html_content | regex_replace(']+>', '') }}"
This should extract the actual string that is within the HTML tags as demonstrated by the resulting output:
"msg": "Greetings from Linuxhint!"
}
Example 5: Date Formatting
Another common usage of regular expressions is date formatting. For example, we can use the regex_replace module to format a date from YYYY/MM/DD to DD-MM-YYYY as follows:
- hosts: localhost
vars:
date_string: "Today's date is 2023/07/27"
tasks:
- name: Format Date
debug:
msg: "{{ date_string | regex_replace('^(.*?)(\\d{4})/(\\d{2})/(\\d{2})', '\\1\\4-\\3-\\2') }}"
Output:
"msg": "Today's date is 27-07-2023"
}
There you have it!
Remember that since a backslash is an escape character in YAML, you need to double it (\\) in your regular expressions.
You can also employ the (?i) at the beginning of your regex pattern for case-sensitive matching.
Conclusion
You learned how to use the regex_replace feature in Ansible to perform the regular expression pattern matching and replacement in string data with ease. You also come across multiple examples that demonstrate how to use this module to perform various tasks.
