正则表达式基本语法及进阶用法超详细版

using system;
using system.text.regularexpressions;

public class emailvalidator
{
    public static bool isvalidemail(string email)
    {
        // 正则表达式：^[a-za-z0-9._%+-]+@[a-za-z0-9.-]+\.[a-za-z]{2,}$
        string pattern = @"^[a-za-z0-9._%+-]+@[a-za-z0-9.-]+\.[a-za-z]{2,}$";
        return regex.ismatch(email, pattern);
    }

    public static void main()
    {
        string[] emails = {
            "test@example.com",
            "user.name+tag@example.co.uk",
            "invalid-email",
            "another.invalid@.com"
        };

        foreach (var email in emails)
        {
            console.writeline($"{email}: {isvalidemail(email)}");
        }
    }
}

test@example.com: true
user.name+tag@example.co.uk: true
invalid-email: false
another.invalid@.com: false

public class phonevalidator
{
    public static bool isvalidphone(string phone)
    {
        // 正则表达式：^1[3-9]\d{9}$
        string pattern = @"^1[3-9]\d{9}$";
        return regex.ismatch(phone, pattern);
    }

    public static void main()
    {
        string[] phones = {
            "13812345678",
            "19987654321",
            "1234567890",
            "138123456789"
        };

        foreach (var phone in phones)
        {
            console.writeline($"{phone}: {isvalidphone(phone)}");
        }
    }
}

using system;
using system.text.regularexpressions;

class linkextractor
{
    static void main()
    {
        string html = @"
            <a href=""https://www.example.com" rel="external nofollow" ">example</a>
            <a href=""https://www.google.com" rel="external nofollow" ">google</a>
            <img src=""image.jpg"">
        ";

        // 正则表达式：<a\s+href=""([^" rel="external nofollow"  rel="external nofollow" "]*)""
        string pattern = @"<a\s+href=""([^" rel="external nofollow"  rel="external nofollow" "]*)""";
        matchcollection matches = regex.matches(html, pattern);

        foreach (match match in matches)
        {
            console.writeline(match.groups[1].value);
        }
    }
}

https://www.example.com
https://www.google.com

class numberextractor
{
    static void main()
    {
        string input = "订单号：20230518001，金额：99.9元，数量：10";
        string pattern = @"\d+\.?\d*"; // 匹配整数或小数

        matchcollection matches = regex.matches(input, pattern);
        foreach (match match in matches)
        {
            console.writeline(match.value);
        }
    }
}

20230518001
99.9
10

class textreplacer
{
    static void main()
    {
        string input = "手机号：15112347676，身份证号：410123194910011234";
        
        // 替换手机号中间4位为****
        string phonepattern = @"(1[3-9])\d{4}(\d{4})";
        string result = regex.replace(input, phonepattern, "$1****$2");

        // 替换身份证号中间8位为********
        string idpattern = @"(^\d{6}|\d{8})(\d{4}$)";
        result = regex.replace(result, idpattern, "$1********$2");

        console.writeline(result);
    }
}

手机号：151****7676，身份证号：410123********1234

class dateformatter
{
    static void main()
    {
        string input = "today is 11/21/2025";
        string pattern = @"\b(\d{2})/(\d{2})/(\d{4})\b";
        
        // 替换为 yyyy-mm-dd
        string result = regex.replace(input, pattern, "$3-$1-$2");
        console.writeline(result);
    }
}

today is 2025-11-21

class logparser
{
    static void main()
    {
        string log = "[2025-11-21 14:30:00] [info] user 'admin' logged in.";
        
        string pattern = @"\[(.*?)\] \[(.*?)\] (.*)";
        match match = regex.match(log, pattern);

        if (match.success)
        {
            string timestamp = match.groups[1].value;
            string level = match.groups[2].value;
            string message = match.groups[3].value;
            
            console.writeline($"时间：{timestamp}\n级别：{level}\n内容：{message}");
        }
    }
}

时间：2025-11-21 14:30:00
级别：info
内容：user 'admin' logged in.

class namedgroupexample
{
    static void main()
    {
        string input = "name: john, age: 30, email: john@example.com";
        
        string pattern = @"name: (?<name>\w+), age: (?<age>\d+), email: (?<email>[^,]+)";
        match match = regex.match(input, pattern);

        if (match.success)
        {
            console.writeline($"姓名：{match.groups["name"].value}");
            console.writeline($"年龄：{match.groups["age"].value}");
            console.writeline($"邮箱：{match.groups["email"].value}");
        }
    }
}