Issue with regex in Golang

Question

I am trying to create a regex to parse specific string .

The current string is abcd_1.263.0.15-8zz00df.yml and I want to parse only 1.263.0.15-8zz00df out of it.

Tried already with this expression "_\K.*(?=\.)" but its not working in Golan and giving me pattern error. Can someone please help with this?

https://go.dev/play/p/TrB1yVM3q15 or https://go.dev/play/p/zXlwWBq0rlM — mkopriva, Jan 07 '22 at 07:18

Julio · Accepted Answer · 2022-01-07T11:29:54.870

2

Go uses RE2 regex engine, that does not support lookaheads, lookbehinds and other PCRE goodies like \K

See this comparison of the different regex engines.

You could however use this regex:

[^_-]+-[^.]+

See this demo.

Explained:

[^_-]+   # a character that is not "_" or "-", one or more times
-        # a literal "-"
[^.]+    # a character that is not a dot, one or more times

edited Jan 07 '22 at 11:29

answered Jan 07 '22 at 09:52

Julio

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LeGEC · Answer 2 · 2022-01-07T11:25:13.740

1

Just reposting one of @mkopriva's snippets with a sentence,

not everything needs to be done with regular expressions :

    s := "abcd_1.263.0.15-8zz00df.yml"

    if i := strings.IndexByte(s, '_'); i > -1 {
        s = s[i+1:]
    }
    if i := strings.LastIndexByte(s, '.'); i > -1 {
        s = s[:i]
    }

    fmt.Println(s)

playground

edited Jan 07 '22 at 11:25

answered Jan 07 '22 at 09:49

LeGEC

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Stefan Zhelyazkov · Answer 3 · 2022-01-07T09:26:09.603

0

Edit: You can simply use the regular expression:

_(.*)\.

The * matches greedily, which means that it will match everything until the last '.' - this is exactly what you need. Your match is in group 1.

Why are you using the \K matcher? Your regular expression works like this:

_(.*)(?=\.)

and group 1 contains your match.

Note: a very helpful tool to test regular expressions is this site: https://regexr.com/

edited Jan 07 '22 at 09:26

answered Jan 07 '22 at 08:02

Stefan Zhelyazkov

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I tried this but getting error when using ? https://regex101.com/r/I9r2kw/1 – john watson Jan 07 '22 at 09:15
@johnwatson I simplified the regex and it should work now. – Stefan Zhelyazkov Jan 07 '22 at 09:26
thanks @Stefan..but new pattern is including underscore and dot from starting n ending which is not expected – john watson Jan 07 '22 at 09:34
You should use group 1 because the match you need is in group 1. You can see it on the right side on your regex101 link. Learn more about groups here: https://stackoverflow.com/a/14484091/9698467 – Stefan Zhelyazkov Jan 07 '22 at 09:40
thanks @Stefan.. can u also please tell how I can use this group 1... – john watson Jan 07 '22 at 10:16

score 0 · Answer 4 · answered Jan 07 '22 at 13:04

For a bit more precise match for that string format, you can use a capture group, and as there do not seem to be spaces in the string you can use \S instead of .

_(\S+)\.yml$

_ Match the leading underscore
(\S+) Capture 1+ non whitespace chars in group 1
\.yml Match .yml
$ End of string

See a regex demo.

For example

package main
import (
    "fmt"
    "regexp"
)

func main(){
    re := regexp.MustCompile(`_(\S+)\.yml$`)
    res := re.FindStringSubmatch("abcd_1.263.0.15-8zz00df.yml")
    fmt.Printf("%v", res[1])
}

Output

1.263.0.15-8zz00df

Or a broader match, capturing till before the last occurrence of the dot:

_(\S+)\.

See another regex demo.

Issue with regex in Golang

4 Answers4