Regex for matching everything until first occurence of string in Golang flavor

Question

I have the following string:

my-name-host1.host2.host3.com:80

I'm looking for a regex which matches everything until the string -host1.host2.host3.com:80, i.e. the result shall be:

my-name

My current regex in JavaScript seems to be working. The problem is that I need this regex in a "Golang flavor".

https://regex101.com/r/ebSTuq/1

When switching it to Golang I get this regex with a pattern error:
.*(?=\Q-host1.host2.host3.com:80\E)

The preceding token is not quantifiable.

Use `(.*?)-host1\.host2\.host3\.com:80`. Or probably just `^[^-]+-[^-]+`. — Wiktor Stribiżew, May 09 '19 at 12:00
Golang's re2 doesn't support lookarounds, you can check supported syntaxes [here](https://github.com/google/re2/wiki/Syntax). — Aaron, May 09 '19 at 12:05

score 1 · Accepted Answer · answered May 09 '19 at 12:04

Go regex engine is RE2, and RE2 does not support lookarounds.

Actually, you do not need the lookahead: use the non-greedy dot pattern at the start, capture it into Group 1 and use the rest of the pattern as is to check the right hand context:

str := `my-name-host1.host2.host3.com:80`
re := regexp.MustCompile(`(.*?)-host1\.host2\.host3\.com:80`)
match := re.FindStringSubmatch(str)
fmt.Println(match[1])

Output: my-name, see the Go demo.

Note the use of the FindStringSubmatch function that allows access to captured substrings.

Also, see the Go regex demo.

Regex for matching everything until first occurence of string in Golang flavor

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