How to use regular expressions in golang to verify whether the URL address is a third-level domain name

When writing Golang applications, it is often necessary to verify URL addresses. In this process, regular expressions can be a very useful tool that can help effectively check the correctness of URL addresses.

This article will introduce how to use regular expressions to verify whether the URL address is a third-level domain name.

1. Understand the basic knowledge of regular expressions

Regular expression is a language used to describe text patterns. In Golang's regular expressions, some common symbols and representation methods include:

1. "." represents any character.
2. "*" means matching the previous character or expression zero or more times.
3. " " means matching the previous character or expression one or more times.
4. "?" means matching the previous character or expression zero or one time.
5. "d" represents a number.
6. "w" represents any word character, including letters, numbers and underscores.

2. Write a regular expression to match the URL address of the third-level domain name

Let’s write a regular expression to match the URL address of the third-level domain name. The third-level domain name refers to the three parts in the hostname (hostname) part of the URL. For example: www.example.com, blog.example.com, etc.

^(www.)?([a-zA-Z0-9] ).([a-zA-Z0-9] ).([a-zA-Z0-9] )$

Analysis:

1, ^ represents the beginning of the matching string;
2, (www.)? represents the optional www. prefix;
3, ([a-zA -Z0-9] ) represents the first part of the third-level domain name;
4, . represents the separator;
5, ([a-zA-Z0-9] ) represents the second part of the third-level domain name ;
6, . represents the delimiter;
7, ([a-zA-Z0-9] ) represents the third part of the third-level domain name;
8, $ represents the end of the matching string.

3. Use regular expressions to verify URL addresses in Golang

Using regular expressions in Golang requires the use of the "regexp" package. This package provides the "MatchString" function, which can be used to match regular expressions.

The following is a complete Golang sample program that demonstrates how to use regular expressions to verify whether the URL address is a third-level domain name.

package main

import (
    "fmt"
    "regexp"
)

func main() {
    url := "www.example.com"
    if matchUrl(url) {
        fmt.Printf("%s 是三级域名
", url)
    } else {
        fmt.Printf("%s 不是三级域名
", url)
    }

    url = "blog.example.com"
    if matchUrl(url) {
        fmt.Printf("%s 是三级域名
", url)
    } else {
        fmt.Printf("%s 不是三级域名
", url)
    }

    url = "example.com"
    if matchUrl(url) {
        fmt.Printf("%s 是三级域名
", url)
    } else {
        fmt.Printf("%s 不是三级域名
", url)
    }
}

func matchUrl(url string) bool {
    re := regexp.MustCompile(`^(www.)?([a-zA-Z0-9]+).([a-zA-Z0-9]+).([a-zA-Z0-9]+)$`)
    return re.MatchString(url)
}

In the above program, we first define a URL address. Then call the "matchUrl" function, passing the URL address as a parameter.

In the "matchUrl" function, we use the "regexp.MustCompile" function to compile the regular expression. Then use the " re.MatchString " function to match whether the URL address meets the requirements of the regular expression. The function returns true if the match is successful, false otherwise.

As you can see, in the above example program, we verified the three URL addresses www.example.com, blog.example.com, and example.com respectively. Only the first two match the third-level domain names. requirement, so the output result is:

www.example.com 是三级域名
blog.example.com 是三级域名
example.com 不是三级域名

Summary:

It is not difficult to use regular expressions in Golang to verify whether the URL address is a third-level domain name. Just write a regular expression that meets the conditions, and then match it through the functions provided in the "regexp" package.

I hope the introduction of this article can be helpful to you!

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