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

It is a common requirement to use regular expressions in golang to verify whether the URL address is a second-level domain name. In this article, we will introduce how to use regular expressions in golang for verification, and how to write regular expressions to verify whether a URL address is a second-level domain name.

First, let’s take a look at the basic usage of regular expressions in golang. Golang provides a regular expression library regexp. We can use regular expressions by calling the regexp package.

Before using regular expressions for verification, we need to write regular expressions first. The following is a regular expression that represents a second-level domain name:

^[a-zA-Z0-9]+([-.]{1}[a-zA-Z0-9]+)*.[a-zA-Z]{2,5}$

The meaning of this regular expression is: Match a string whose first letter can be an uppercase or lowercase letter or a number, and can include but is not limited to hyphens and periods. , a string that ends with an English letter and has a length of 2-5.

Then let’s take a look at how to use this regular expression for verification in golang. The following is a sample code that uses regular expressions to verify whether the URL is a second-level domain name:

package main

import (
    "fmt"
    "regexp"
)

func main() {
    url := "http://www.example.com"

    re := regexp.MustCompile(`^[a-zA-Z0-9]+([-.]{1}[a-zA-Z0-9]+)*.[a-zA-Z]{2,5}$`)
    match := re.MatchString(url)

    if match {
        fmt.Println("URL是一个二级域名")
    } else {
        fmt.Println("URL不是一个二级域名")
    }
}

In the above code, we first define a URL to be verified. In the next code, we call The function MatchString in the regexp package is used. This function is used to determine whether the string to be verified conforms to the specified regular expression. If it matches, return true, otherwise return false.

In actual use, we may encounter some special situations, such as some special characters in the URL, and we need to escape these special characters. Another situation is that we need to ignore the case in the URL. In this case, we need to use the ignore case option in the regular expression. The following is a sample code that uses regular expressions to verify whether the URL is a second-level domain name and ignores case and special characters:

package main

import (
    "fmt"
    "regexp"
)

func main() {
    url := "http://wwW.ExaMPle.com?foo=bar"

    re := regexp.MustCompile(`(?i)^[a-z0-9]+([-.]{1}[a-z0-9]+)*.[a-z]{2,5}$`)
    match := re.MatchString(url)

    if match {
        fmt.Println("URL是一个二级域名")
    } else {
        fmt.Println("URL不是一个二级域名")
    }
}

In the above code, we first define a URL to be verified, and then In the following code, we call the function MatchString in the regexp package. This function is used to determine whether the string to be verified conforms to the specified regular expression. (?i) means ignoring case, [a-z0-9] ([-.]{1}[a-z0-9] )*.[a-z]{2,5}$ means matching a second-level domain name.

To sum up, it is a common requirement to use regular expressions to verify whether the URL is a second-level domain name. golang provides the regexp package to support the use of regular expressions. We only need to write the corresponding regular expression and use the MatchString function to verify it. It should be noted that some special characters need to be escaped, and there are also cases where case and special characters need to be considered.

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