Regex not matching in Go

Question

I have a regex that is not matching in Go.

However in a regex playground it's matching fine: https://regex101.com/r/VNDXcQ/2.

It's matching JS comments.

Here is the code:

comment := "// fallback response. For more information contact support"
re := regexp.MustCompile(`/\/\*[\s\S]*?\*\/|([^\\:]|^)\/\/.*$/gm`)
matches := re.MatchString(comment)
fmt.Println(matches) // false

Why could that be?

Who is submitting a close-vote with the reason as "Not reproducible or was caused by a typo"? What exactly in the example code provided in the question is not reproducible? The specified behavior is 100% reproducible. Here is the Go playground for it: play.golang.org/p/muUxpBOmOQV. It produces the output false exactly as mentioned in this question. Really, who is it that is going around close-voting most Go questions with this fake reason? Why are they doing this? — Lone Learner
– Lone Learner, Commented Aug 21, 2020 at 11:38
@LoneLearner: Totally agree with your point. From the many tags I follow, only here do I notice, more than decent questions with a proper MCVE getting downvoted and voted to close — Inian
– Inian, Commented Aug 21, 2020 at 11:46

Wiktor Stribiżew · Accepted Answer · 2020-08-21 10:52:24Z

5

There are two major issues:

You are using a regex literal as a string regex pattern. It means, you need to remove the first and last / and "move" m flag to the pattern by converting it into a (?m) inline modifier
You are only match the first occurrence with MatchString (since flags cannot be passed along with the regex pattern and g flag "is not supported"). You need to use FindAllString to get all matches.

You can fix that with

re := regexp.MustCompile(`(?m)/\*[\s\S]*?\*/|([^\\:]|^)//.*`)
matches := re.FindAllString(comment, -1)

Note / is not a special character and thus needs no escaping.

See Go playground.

answered Aug 21, 2020 at 10:52

Wiktor Stribiżew

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