How to use regular expressions in golang to verify whether the URL address is an 11th-level domain name

In Golang, regular expressions are a powerful tool that can be used to verify whether a URL address is an 11th-level domain name. In this article, we'll explore how to achieve this using regular expressions.

1. What is an 11th-level domain name?

In the Internet, a domain name is a string used to identify network resources. Domain names are divided according to the hierarchical structure, from high to low: "root domain name", "top-level domain name", "second-level domain name", "third-level domain name", "fourth-level domain name"... all the way to "eleven-level domain name".

A typical 11th level domain name is as follows:

www.example.com.cn.foo.bar.baz.qux.fred.plugh.xyz

2. Regular expression verification rules

We can use regular expressions to verify whether the URL address is an 11th-level domain name. For a legal 11th-level domain name, it must meet the following conditions:

• The length of the domain name shall not exceed 253 characters;
• The length of the domain name at all levels shall not exceed 63 characters;
• The length of the domain name at all levels shall only consist of letters, numbers and dashes ( "-");
• The domain name must end with letters or numbers.

Based on the above rules, we can write the following regular expression:

^[a-zA-Z0-9]([a-zA-Z0-9-]{ 0,61}[a-zA-Z0-9])?.([a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9 ])?.){9}[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?$

In the above regular expression, ^ means matching the beginning of the string, $ means matching the end of the string. Other characters in the regular expression indicate matching corresponding characters, for example:

• [a-zA-Z0-9] indicates matching letters and numbers;
• - indicates matching horizontal lines (Note that the escape character "" is required);
• {0,61} means matching 0 to 61 characters.

3. Golang implements regular expression verification

In Golang, you can use the regexp package to process regular expressions. For our needs, you can use the following code:

package main

import (
    "fmt"
    "regexp"
)

func main() {
    url := "www.example.com.cn.foo.bar.baz.qux.fred.plugh.xyz"
    regex := "^[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.([a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.){9}[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?$"
    matched, _ := regexp.MatchString(regex, url)
    if matched {
        fmt.Println("URL地址为11级域名")
    } else {
        fmt.Println("URL地址不是11级域名")
    }
}

In the above code, we first define a URL address, and then use the MatchString function to perform regular expression matching on it. If the match is successful, it means that the URL address is an 11th-level domain name.

4. Summary

Through the study of this article, we learned how to use regular expressions to verify whether the URL address is an 11th-level domain name, and implemented this function in Golang . When we need to verify the URL address, we can write regular expressions according to similar rules and use Golang's regexp package for processing.

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