I want to get 10.10.10.10 from 10.10.10.10:9445, i.e. parsing before the :.
I tried on regex101 using: (.+?((?=:))) and it worked there. But couldn't get what I want on Grafana.
It doesn't throw error on that regex but also doesn't return result.
Can someone please let me know what causes this ?
You need to use a regex that matches the full string and use a capturing group around the part of pattern you need to get:
([^:]+):.*
It will match and capture any 1 or more chars other than : from the start of the string till the first :, then will match : and any 0 or more chars other than line break chars till end of the string (with no linebreaks).
See the regex demo.