This topic explains how to effectively use regular expressions (regex) within Discourse’s Watched Words feature.
If your site is hosted with Discourse, please reach out to team@discourse.org if you would like to enable this setting.
Regular expressions (regex) are a powerful tool for defining search patterns. You can use regex in the Watched Words feature to enhance the accuracy and flexibility of word filtering on your Discourse site.
To use regular expressions (regex) in watched words you must first turn on the
watched words regular expressionssite setting.
Regex is extremely powerful and thus dangerous. An incorrectly written regex statement can cause issues for your users. Test your regex statements on non-production instances before going live.
Example Regex patterns
Here are some common regex patterns and how they can be employed:
Case-insensitivity
By default, Discourse matches both uppercase and lowercase forms of a word.
thread
This will match thread, THREAD, and thReAd.
Character alternatives
Use character alternatives to expand your matches.
(t|7)hr(3|e)(4|a)d
This will match all of the cases above, plus thr3ad, 7hread, and thr34d.
threads?\S+
This will match thread and threads but not threaded or threading.
Word boundaries
Regex patterns can unintentionally match parts of words. Use word boundaries to avoid partial matches.
\bthreads?\b
This matches thread and threads but avoids matches like threadlike or unthreading.
Handling Unicode characters
Standard word boundaries may fail with Unicode characters. Create boundaries for characters not handled well by JavaScript regex.
gr(ü|ue)(ß|ss)e
This matches all commonly spelled forms of the word grüße — including gruesse and GRÜSSE
Say you want to block the word Über, but not Übersicht. Using word boundaries like \b(ü|ue)ber\b doesn’t work because some of the JavaScript regex word flags don’t handle Unicode characters.
Instead you have to make your own boundaries.
(?:^|\s)(ü|ue)ber\b
This will now appropriately match Über and ueber, but not Übersicht or uebersicht.
Additional Information
Regex capture and replace is not supported in Watched Words, only matching, so this will not work on the link or replace actions.
Last edited by @SaraDev 2024-08-02T19:09:22Z
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