Testing preprocessing regexes with regex101.com

[troffasky]

Server 7.0.22.
I am trying to write a template to collect metrics from cloudflared.
Master item fetches
web.page.get[127.0.0.1,/metrics,20241]
This outputs something like:

HTTP/1.1 200 OK

Connection: close

Transfer-Encoding: chunked

Content-Type: text/plain; version=0.0.4; charset=utf-8; escaping=underscores

Date: Mon, 16 Feb 2026 09:32:01 GMT



# HELP build_info Build and version information
# TYPE build_info gauge
build_info{goversion="go1.24.11",revision="2026-01-20-11:14 UTC",type="",version="2026.1.1"} 1
# HELP cloudflared_config_local_config_pushes Number of local configuration pushes to the edge
# TYPE cloudflared_config_local_config_pushes counter
cloudflared_config_local_config_pushes 0
# HELP cloudflared_config_local_config_pushes_errors Number of errors occurred during local configuration pushes
# TYPE cloudflared_config_local_config_pushes_errors counter
cloudflared_config_local_config_pushes_errors 0
....many many more lines...

This is my regex for collecting a metric:

(?<=^cloudflared_config_local_config_pushes ).*

You can see it matches the value 0:



Preprocessing on dependent item created as follows [just trust me that this is the regex as above in the box]:



But this does not work. Always returns:

Preprocessing failed for: HTTP/1.1 200 OK..Connection: close..Transfer-Encoding: chunked..Content-Type: text/plain; version...
1. Failed: cannot perform regular expression "(?<=^cloudflared_config_local_config_pushes ).*" match for value of type "none": pattern does not match

Why is the type 'none'? Obviously I want numeric but set it to Text to help debug. What is wrong with my regex?

[guntis_liepins]

One note: zabbix uses PCRE/PCRE2 (depends on version) regular expressions without gm modifiers.
This worker for me
(cloudflared_config_local_config_pushes_errors)(\s +)(\d+)
Capture group \3 (Output)
I have no idea why lookbehind does not work

[troffasky]

Thanks for looking at this, but that also doesn't work in Zabbix, with the same error [I have tried with and without ^]

Preprocessing failed for: HTTP/1.1 200 OK..Connection: close..Transfer-Encoding: chunked..Content-Type: text/plain; version...
1. Failed: cannot perform regular expression "(^cloudflared_config_local_config_pushes)(\s +)(\d+)" match for value of type "none": pattern does not match

That regex doesn't work with regex101 FWIW:

[guntis_liepins]

Zabbix run regexp without gm modifier. Disable them in regex101.

[troffasky]

Guess what does work, though?

(^HTTP/1.1) (\d+)             \2

Returns "200".
And what does not work?

(^Connection:) (.+)          \2

Same type "none" error.
This does work though:

(Connection:) (.+)          \2

Returns "Close".
Anchoring with ^ is causing me a problem. ^ only works on Line 1.

[troffasky]

Do not need ^, I can trick it into working with \n

(\ncloudflared_config_local_config_pushes) (\d+)          \2

returns 0 as expected.

[guntis_liepins]

oh my regexp had extra space slipped in when paste

[troffasky]

Documentation for regex preprocessing is poor.

https://www.zabbix.com/documentation/current/en/manual/config/items/preprocessing#regexp

says "Please refer to regular expressions section for some existing examples"

https://www.zabbix.com/documentation/current/en/manual/regular_expressions#example

Has no examples of preprocessing regexes.
Even just a link to some factory templates that use it would be a start!

[cyber]

Looking at example data in first post... Isn't this prometheus output? You could just use prometheus related preprocessing for it instead of torturing yourself with regexes?

https://www.zabbix.com/documentation/7.0/en/manual/config/items/itemtypes/prometheus

[troffasky]

I wouldn't know Prometheus if it bit me on the a***. So if you say it is then I guess it is Shame you did not reply on 16th
TBH it's not obvious to me that it's any easier than regexes but using the Prometheus LLD is probably where the real value is:

https://www.zabbix.com/documentation/7.0/en/manual/discovery/low_level_discovery/examples/prometheus

I manually created 4 instances of many metrics [because it looks like cloudflared always establishes 4 tunnels] which LLD would have been better for.

[cyber]

And now you know..