How do I match exactly a partial string in regexp and ignore any characters before and after a pattern?

Question

I am using golang regexp and I want to extract a pattern in a string.

For example, I can have the following name value pairs in the string:

"name1=val1;name2=val2;needle=haystack;name3=val3"

I am looking for exactly the string "needle=haystack" and discard anything else.

It would be even better if I could just get the result to be exactly haystack.

How do I do this with regexp in golang?

Answer 1

I'm not entirely clear on what the goal is. If you're always looking for needle=haystack then you can use strings.Contains(str, "needle=haystack").

If you really want to do it with regexes then it would be something like the code below.

package main

import (
    "fmt"
    "regexp"
)

func main() {
    str := "name1=val1;name2=val2;needle=haystack;name3=val3"

    r := regexp.MustCompile("needle=([a-z]+);")
    found := r.FindString(str)
    if found == "" {
        fmt.Println("No match found")
        return
    }
    fmt.Println(found) // needle=haystack;

    submatches := r.FindStringSubmatch(str)
    fmt.Println(submatches) // [needle=haystack; haystack]
    if len(submatches) < 2 {
        fmt.Println("No submatch found")
        return
    }
    fmt.Println(submatches[1]) // haystack
}