如何使用C#的正则表达式匹配行的开头或结尾？

using System.Text.RegularExpressions;

string input = "This is a sample text.\nAnother line.";

// 匹配行的开头
Regex lineStartRegex = new Regex(@"^");
MatchCollection lineStartMatches = lineStartRegex.Matches(input);
foreach (Match match in lineStartMatches)
{
    Console.WriteLine($"Line start: {match.Value}");
}

// 匹配行的结尾
Regex lineEndRegex = new Regex(@"$");
MatchCollection lineEndMatches = lineEndRegex.Matches(input);
foreach (Match match in lineEndMatches)
{
    Console.WriteLine($"Line end: {match.Value}");
}

Regex lineStartRegex = new Regex(@"^", RegexOptions.Multiline);