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
}