Regular expressions (regex) are special sequences of characters used to find, extract, replace, or match text. They are powerful tools for text processing tasks in data analysis. In the context of Google Tag Manager (GTM) and Google Analytics 4 (GA4), regex can be used for trigger conditions, Regex table variables, filtering data in reports, and more.

In GTM, regex can be used for trigger conditions by specifying a section that says, “This trigger fires on”. This allows you to restrict the trigger to fire only on certain variable conditions, such as custom JavaScript, Data Layer variables, built-in variables, etc. For example, using the Element Visibility Trigger, you can track when a user views an element with a specific ID across multiple pages by setting “Page path matches RegEx” with the appropriate pattern.

To filter data in GA4 reports using regex, you can either use the “Add filter” button or customize the report. When filtering, you can choose dimensions and select one of the regex options like “matches regex” or “does not match regex” and enter your pattern. For example, to filter a report to include visitors from Canada or the USA, you would select “Country” as the dimension, choose “matches regex”, and enter the pattern Canada|USA.

In GA4, you can create and modify events directly in the interface, which is useful for creating a version of an existing event without using GTM or a developer. Navigate to Admin > Data display > Events > Create events. Here, you can combine events or create new ones based on certain conditions using regex patterns. For instance, to combine form_submission and generate_lead events under a new event called form_completed, you would specify the conditions and regex pattern that captures both events.

Some basic regex syntax and patterns include:

• Wildcards like the period . (matches any single character), question mark ? (matches the previous character 0 or 1 times), plus + (matches the previous character at least once), asterisks * (matches the previous character 0 or more times), and pipe | (used as an OR statement).
• Anchors like caret ^ (matches the beginning of the string) and dollar sign $ (matches the end of the string).
• Escape character \ (used to interpret the next character literally).
• Groups including parentheses () (matches the exact order of characters), square brackets [] (matches any order of characters within), hyphen - (creates a range within square brackets), and curly brackets {} (defines the number of times characters appear).

For example, to match a URL pattern for a shoe page with a specific ID format, you could use a regex pattern like .*\/shoe\/[0-9]{3}-[0-9]{6}$.