package main
import (
"regexp"
"fmt"
)
func main() {
var re = regexp.MustCompile(`(?im)^(?:[_a-z0-9](?:[_a-z0-9-]{0,61}[a-z0-9])?\.)+(?:[a-z](?:[a-z0-9-]{0,61}[a-z0-9])?)?$`)
var str = `This regexp can be used to validate domain names in Golang. While it cannot enforce the 253 character limit (with optional trailing period not included) that can be easily done by a simple len(domain) <= 253 check as well.
This can be used as-is in other languages, even with RE2 regex engine. If positive lookbehind assertions are available, the character limit can be used.
Non-capturing groups are used.
Example validated domains (some may be invalid per TLD rules):
example.com
_25._tcp.SRV.example
punycoded-idna.xn--zckzah
under_score.example
Example invalid domains:
192.0.2.1
has spaces.com
easy,typo.example
domain\.escapes.invalid
no_trailing_.invalid
-leading-or-trailing-.hyphens.invalid
TLDs have more validation, the following will not validate:
example
digit.1example
underscore._example_com
but with a trailing period, the same rules as non-TLD are applied:
example.
192.0.2.1.
digit.1example.
underscore._example_com.
`
for i, match := range re.FindAllString(str, -1) {
fmt.Println(match, "found at index", i)
}
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Golang, please visit: https://golang.org/pkg/regexp/