Published on 2025-06-26T05:22:07Z

What is a Regular Expression? Examples and Use in Analytics

Regular Expressions (regex) are sequences of characters that define search patterns. In analytics, regex is crucial for filtering data streams, segmenting user behavior, and extracting insights from URLs, event names, and more. Tools like GA4 and Plainsignal leverage regex to refine reports, enabling advanced filtering and goal tracking. By mastering regex, analysts can isolate specific traffic sources, unify varied event names, and automate complex data transformations. We’ll also cover common pitfalls and tips for crafting efficient patterns.

Illustration of Regular expression
Illustration of Regular expression

Regular expression

Regex is a pattern-based syntax used in analytics to filter, segment, and manipulate data in platforms like GA4 and Plainsignal.

What is a Regular Expression?

Regular expressions, often shortened to regex, are a declarative syntax for describing text patterns. They combine literals and metacharacters to match sequences, enabling powerful text searching and manipulation. In analytics, regex underpins tasks like URL filtering, event matching, and data segmentation.

  • Literals and metacharacters

    Literals match exact characters, while metacharacters like ., *, and + provide wildcard and repetition functionality.

    • Literals:

      Direct characters that match themselves exactly.

    • Metacharacters:

      Symbols with special meanings, such as . (any character) and * (zero or more occurrences).

  • Quantifiers and anchors

    Quantifiers ({n,m}, *, +) specify how many times a token should appear; anchors (^, $) assert positions at the start or end of a string.

    • Quantifiers:

      Define repetition counts, e.g., + for one or more occurrences.

    • Anchors:

      ^ anchors to the start, $ anchors to the end of the string.

Why Regular Expressions Matter in Analytics

Regex enables analysts to define custom filters and segments beyond simple exact matches, allowing grouping of related pages, exclusion of noise, and unification of varied event names. With tools like GA4 and PlainSignal, regex-based conditions unlock deeper insights and flexible reporting.

  • Custom url filtering

    Use regex to include or exclude page paths. For example, ^/docs/.* captures all documentation pages.

  • Advanced event segmentation

    Group events with similar names or parameters using regex, such as purchase_.* to capture all purchase-related events.

Examples in Plainsignal and GA4

Below are practical examples of applying regex filters in PlainSignal and GA4, including inline code snippets and UI configurations.

  • Plainsignal: filtering pageviews by regex

    In PlainSignal’s dashboard filter input, switch to regex mode and enter a pattern like ^/blog/.*$ to view only blog pageviews. Alternatively, inject a regex filter via the tracking snippet:

    • Tracking snippet example: 
      <link rel="preconnect" href="//eu.plainsignal.com/" crossorigin />
<script defer data-do="yourwebsitedomain.com" data-id="0GQV1xmtzQQ" data-api="//eu.plainsignal.com" src="//cdn.plainsignal.com/PlainSignal-min.js"></script>
<script>
  PlainSignal('setFilter', 'page_path', '^/blog/.*$');
</script>

  • Ga4: creating regex-based filters

    In GA4, navigate to Admin → Data Streams → Configure Tagging Settings or to the Events section and add a filter. Use the ‘matches regex’ operator. For example, to capture product pages:

    • Ga4 filter example: 
      Parameter: page_location
Operator: matches regex
Value: ^https://www\.example\.com/products/.*

Best Practices and Tips

To ensure maintainable and efficient regex in analytics, follow these recommendations.

  • Keep patterns simple

    Avoid overly complex expressions; break them into smaller, reusable components.

  • Escape special characters

    Prefix metacharacters with backslashes when matching them literally.

    • Common escapes:

      Characters like ., +, *, ?, ^, and $ should be escaped with \\.

  • Test and validate

    Use online regex testers (e.g., regex101.com) or built-in tool previews to validate patterns before deploying.

  • Use anchors wisely

    Anchors (^ and $) improve performance by localizing matches to string boundaries.

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