Wildcard in PromQL "5.+" vs "5\\d{2}"

[Jason]

Hi

I will write my query like this (with * wildcad)

sum(http_requests_total{status_code=~"5.+"})

In internet I found this syntax \\d{2}

sum(http_requests_total{status_code=~"5\\d{2}"})

What is this? Where to find more info?
Why I should use the 2nd query and not the first?

cheers
Jason

[Stuart Clark]

In reality both will do the same thing, although the second is
technically more correct.

The first regular expression is matching "5" followed by 1 or more other
characters, while the second is matching "5" followed by exactly 2
numbers. So the first one would also match "50" or "5frogs" which aren't
valid status codes, but in reality your application would have to be
having serious problems to be setting those values anyway.

--
Stuart Clark

[Jason]

On 03.10.2023 10:55, Stuart Clark wrote:
> In reality both will do the same thing, although the second is
> technically more correct.
>
> The first regular expression is matching "5" followed by 1 or more other
> characters, while the second is matching "5" followed by exactly 2
> numbers. So the first one would also match "50" or "5frogs" which aren't
> valid status codes, but in reality your application would have to be
> having serious problems to be setting those values anyway.

Thanks Stuart

Is there any docs about this type of regex? I didn't found "\\d" in
official docs.

How is this regex called?

cheers
Jason

[Julius Volz]

Hi Jason,

Prometheus uses the RE2 regular expression dialect, you can find the documentation about that here: https://github.com/google/re2/wiki/Syntax

The double backslash ("\\") is just to escape the one backslash in the Prometheus string. So the actual regex is just "5\\d{2}". You can remove the escaping by using backticks as quotes, which do not interpret escape sequences: `5\d{2}`

Kind regards,

Julius

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Julius Volz

PromLabs - promlabs.com