regex - How to match a substring after X occurrences of a pattern?

ab1-cde23-fg45-h6-ijk-789.lmn.local.        86400 IN A  12.34.5.123

In the follow DNS entry, I'm trying to match the h6 section (position 4). At this point, I know this section of the domain is only composed of 2 letters/digits or one of each, so I can match it (in a clumsy way) with

"-[a-zA-Z0-9]{2}-"

In a case where I could not assume that this is the only section of a domain with 2 letters/digits, how could I match only the content of the 4th position minus the -? (ab1 being the first position, cde23 the second, and so on, with all the positions separated by -)

I'm able to match up to the 4th positions with the following regex, but it includes everything from the start.

"([a-zA-Z0-9]*-){3}[a-zA-Z0-9]*-"

I'm using theses regexp in golang.

Do:

^(?:[^-]+-){3}([^-]+)

• ^(?:[^-]+-){3} matches - separated first 3 fields, (?:) makes the group non-capturing

• The captured group, ([^-]+) will contain the - separated 4th field.

Demo

While we are at this, you should perhaps look at string manipulation rather than costly Regex implementation, plain strings.Split() should do:

package main

import (
	"fmt"
	"strings"
)

func main() {
	s := "ab1-cde23-fg45-h6-ijk-789.lmn.local.        86400 IN A  12.34.5.123"
	fmt.Println(strings.Split(s, "-")[3])
}