Sentence Boundary in GO
Go (RE2) can't run this pattern out of the box.
Try it in the GO tester →Why it doesn't work in GO
Go's RE2 engine doesn't support lookarounds (`(?=...)`, `(?<=...)`, etc.) — they break the linear-time matching guarantee.
Workaround
Restructure to capture the surrounding context as a group instead, or use JS / Python where lookarounds are available.
Pattern
regexGO
[.!?]\s+(?=[A-Z]) (flags: g)How the pattern works
`[.!?]` matches terminating punctuation. `\s+` matches whitespace. `(?=[A-Z])` is a lookahead for a capital letter (marks where the next sentence begins).
Examples
Input
Hello world. How are you? I'm fine!Matches
.?