[Loki + Grafana] Extract Fields Regex Not Working — Log Line Includes ANSI Color Codes

Grafana Dashboards
1

Hi everyone,

I’m trying to visualize response times from logs in a Grafana time series panel using Loki. My log lines come from a NestJS app and look like this (with ANSI color codes for terminal coloring):

[32m[Nest] 1275414  - e[39m04/11/2025, 9:35:12 PM e[32m    LOGe[39m e[38;5;3m[Response] e[39me[32mGET /api/v1/webhook/prod 200 551mse[39m

I added an “Extract fields” transform and used this regex/few different regex to get the duration:

(\d+)ms

Screenshot 2025-04-12 at 03.45.18
Screenshot 2025-04-12 at 03.45.181846×1162 269 KB

Screenshot 2025-04-12 at 03.52.54
Screenshot 2025-04-12 at 03.52.541444×1348 167 KB

But it doesn’t extract anything — the output is always the full log line, not the match group.

Thanks in advance!

2

Try decolorize and pattern parser on the LogQL level

3

You ever figure this out? I’m having the exact issue. I have a simple string in a field and the string always begins with something like “Tier 1” or “Tier 2”. I have the regex of “(Tier [0-9])” but it just always returns the entire string. It honestly doesn’t seem to matter what I put in the RegExp field. It just creates a new field with the entire value of the original field no matter what…

Driving me nuts…

4

For me to get anything to work, I had to make sure I was doing a named capturing group. See New regular expression option for Extract fields transformation | Grafana Labs and click through to the mozilla documentation. e.g., (?yourregex)