Assuming your lookup file isn't too big, you could try something like this | append
[| inputlookup regexlookup.csv
| eval regexlabel=regex.":".label
| stats list(regexlabel) as regexlabel]
| reverse
| filldown regexlabel
| where isnotnull(subject)
| streamstats count as _row
| mvexpand regexlabel
| eval regex=mvindex(split(regexlabel,":"),0)
| eval label=mvindex(split(regexlabel,":"),1)
| eval label=if(match(subject,regex),label,null())
| stats first(_time) as _time first(*) as * by _row
| sort 0 _row
| fields - _row regex regexlabel
... View more