C#使用正则表达式

if (!Regex.IsMatch(this.txtCode.Text.Trim(), @"^[0-9]*$", RegexOptions.Singleline))
    Console.Write("只能输入数字");

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    //退格键(8)、 回车（13）、全选(1)、复制(3)、粘贴(22)
    e.Handled = !(Regex.IsMatch(e.KeyChar, @"\d", RegexOptions.Singleline) || e.KeyChar == (char)8 || e.KeyChar != (char)13);
}

private void textbox1_TextChanged(object sender, EventArgs e)
 {
　　var reg = new Regex("^[0-9]*$");
　　var str = textbox1.Text.Trim();
　　var sb = new StringBuilder();
　　if (!reg.IsMatch(str))
　　{
　　　　for (int i = 0; i < str.Length; i++)
　　　　{
　　　　　　if (reg.IsMatch(str[i].ToString()))
　　　　　　{
　　　　　　　　sb.Append(str[i].ToString());
　　　　　　}
　　　　}
　　　　textbox1.Text = sb.ToString();
　　　　//定义输入焦点在最后一个字符
 　　　　textbox1.SelectionStart = textbox1.Text.Length;
　　}
 }

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using System.Text.RegularExpressions;

if (Regex.IsMatch("a.b.c.d", @"(\w)\.(\w)", RegexOptions.IgnoreCase))
    Console.Write("匹配成功");

Match m = Regex.Match("a.b.c.d", @"(\w)\.(\w)");
if (m.Success)
    Console.Write("Match=" + m.Value + " pos:" + m.Index);
//Match=a.b pos:0

MatchCollection mc = Regex.Matches("a.b.c.d", @"(\w)\.(\w)");
for (int i = 0; i < mc.Count; i++)
{
    Match match = mc[i];
    Console.WriteLine("Match=" + match.Value + " :" + i);

    for (int j = 0; j < match.Groups.Count; j++)
    {
        Group group = match.Groups[j];
        Console.WriteLine("--Group =" + group.Value + " :" + j);
        for (int k = 0; k < group.Captures.Count; k++)
        {
            Console.WriteLine("------Captures =" + group.Captures[k].Value + " :" + k);
        }
    }
}

var mc = Regex.Matches(Server.UrlDecode(client.ResponseHeaders["Content-Disposition"]), @"filename=(.+)");
string filename = mc[0].Groups[1].Value;

Console.WriteLine(Regex.Replace("this test*", "[^a-zA-Z]", "()")); //this()test()
Console.WriteLine(Regex.Replace("sevenyear", @"\w+", m =>
{
    return m.Value.ToUpper();
})
); //SEVENYEAR

string[] s = Regex.Split("first-second-thrid", "-");
for (int i = 0; i < s.Length; i++)
{
    Console.WriteLine(s[i]);
}
//first
//second
//thrid

var temp = Regex.Split("1234abcdef", @"(?<=\G.{4})(?!$)");
temp.ToList().ForEach(t => Console.WriteLine(t));
//1234
//abcd
//ef

var temp = Regex.Split("1234 abcd efa", @"(?<=\S+\b\s+)");
temp.ToList().ForEach(t => Console.WriteLine(t));
//1234
//abcd
//ef

var temp = Regex.Split("1234,abcd,12345,abcd,ab", @"(?<=\G(?:\w+[,，]){2})");
temp.ToList().ForEach(t => Console.WriteLine(t));
//1234,abcd,
//12345,abcd,
//ab

Regex exp= new Regex(@"\w\.\w", RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);
MatchCollection mc = exp.Matches("a.b.c.d");

void Main()
{
    string ss = "259年又62天";
    MatchCollection mc = Regex.Matches(ss, @"(?:(?<year>\d+)年)?又?(?:(?<month>\d+)天)?");
    for (int i = 0; i < mc.Count; i++)
    {
        Match match = mc[i];
        Console.WriteLine("Match[" + i + "]，Value：" + match.Value);

        for (int j = 0; j < match.Groups.Count; j++)
        {
            Group group = match.Groups[j];
            Console.WriteLine("--Group[" + j + "]，Name：" + group.Name + "  ，Value：" + group.Value);
            for (int k = 0; k < group.Captures.Count; k++)
            {
                Console.WriteLine("------Captures[" + k + "]，Value：" + group.Captures[k].Value);
            }
        }
        Console.WriteLine();
    }
}