Filebeat: Check if a String Starts With Number Using Regular Expression

To check if a string starts with a number using Filebeat and regular expressions, you can use the processors configuration in Filebeat. Specifically, you’ll use the grok processor to match patterns in your log lines.

Here's an example of how to configure Filebeat to check if a string starts with a number:

1. Add the grok processor to your Filebeat configuration:

    

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   processors:
     - grok:
         patterns:
           - '^(?<number_start>\\d)'
   

   In this configuration:

- `^(?<number_start>\\d)` is a regular expression where `^` asserts the position at the start of the string, and `\\d` matches any digit. `(?<number_start>\\d)` captures the digit in a named group `number_start`.

1. Use the extracted data:

   You can use the extracted number_start field to filter or manipulate logs based on whether they start with a number.

Here's a more complete example for a typical Filebeat configuration file:

filebeat.inputs:
  - type: log
    paths:
      - /var/log/myapp/*.log

processors:
  - grok:
      patterns:
        - '^(?<number_start>\\d)'
  - drop_fields:
      when:
        not:
          has_fields: ['number_start']

In this example:

• The grok processor checks if the log lines start with a number and captures it.
• The drop_fields processor drops the event if it doesn’t have the number_start field, effectively filtering out log lines that don’t start with a number.

Make sure to adjust the paths and patterns according to your specific use case.

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