在 C# 中移除字符串前后指定的字符串一般使用系统自带的方法即可完成，比如Trim、TrimEnd、TrimStart等方法也。但是当有一些特殊需求的时候，比如重复匹配时，这些方法就不再方便。本文使用正则表达式的方法实现相关需求。

字符串扩展代码实现

public static partial class Extensions
{
	/// <summary>
	/// 移除字符串前后指定的字符串
	/// </summary>
	/// <param name="value">字符串本身</param>
	/// <param name="trimContent">将要移除字符前后的指定内容</param>
	/// <param name="isRepeat">是否允许重复匹配</param>
	/// <returns></returns>
	public static string Trim(this string value, string trimContent = "",bool isRepeat=true)
	{
		if (string.IsNullOrWhiteSpace(value))
		{
			return "";
		}
		if (string.IsNullOrWhiteSpace(trimContent))
		{
			return value.Trim();
		}
		trimContent = Regex.Replace(trimContent, @"([.$\\^*+?\[\]()])", @"\$1");
		string limit = isRepeat ? "+" : "";
		string regexString = $"^(?:{trimContent}){limit}|(?:{trimContent}){limit}$";
		value = Regex.Replace(value, regexString, "");
		return value;
	}

	/// <summary>
	/// 移除字符串开始指定的字符串
	/// </summary>
	/// <param name="value">字符串本身</param>
	/// <param name="trimContent">将要在字符串开始移除的字符</param>
	/// <param name="isRepeat">是否允许重复匹配</param>
	/// <returns></returns>
	public static string TrimStart(this string value, string trimContent = "", bool isRepeat = true)
	{
		if (string.IsNullOrWhiteSpace(value))
		{
			return "";
		}
		if (string.IsNullOrWhiteSpace(trimContent))
		{
			return value.TrimStart();
		}
		trimContent = Regex.Replace(trimContent, @"([.$\\^*+?\[\]()])", @"\$1");
		string limit = isRepeat ? "+" : "";
		string regexString = $"^(?:{trimContent}){limit}";
		value = Regex.Replace(value, regexString, "");
		return value;
	}

	/// <summary>
	/// 移除字符串结尾指定的字符
	/// </summary>
	/// <param name="value">字符串本身</param>
	/// <param name="trimContent">将要在字符串结尾移除的字符</param>
	/// <param name="isRepeat">是否允许重复匹配</param>
	/// <returns></returns>
	public static string TrimEnd(this string value, string trimContent = "", bool isRepeat = true)
	{
		if (string.IsNullOrWhiteSpace(value))
		{
			return "";
		}
		if (string.IsNullOrWhiteSpace(trimContent))
		{
			return value.Trim();
		}
		trimContent = Regex.Replace(trimContent, @"([.$\\^*+?\[\]()])", @"\$1");
		string limit = isRepeat ? "+" : "";
		string regexString = $"(?:{trimContent}){limit}$";
		value = Regex.Replace(value, regexString, "");
		return value;
	}

	/// <summary>
	///通过指定正则表达式替换指定内容
	/// </summary>
	/// <param name="value">字符串本身</param>
	/// <param name="pattern">正则表达式</param>
	/// <param name="replacement">替换内容</param>
	/// <returns></returns>
	public static string Replace(this string value, string pattern, string replacement = "")
	{
		if (string.IsNullOrWhiteSpace(value))
		{
			return "";
		}
		if (string.IsNullOrWhiteSpace(pattern))
		{
			throw new ArgumentException("pattern 不能为空");
		}
		value = Regex.Replace(value, pattern, replacement);
		return value;
	}
	/// <summary>
	/// 通过指定正则表达式替换指定内容
	/// </summary>
	/// <param name="value">字符串本身</param>
	/// <param name="pattern">正则表达式</param>
	/// <param name="replacement">替换内容</param>
	/// <param name="options">正则表达式选项</param>
	/// <returns></returns>
	public static string Replace(this string value, string pattern, string replacement, RegexOptions options)
	{
		if (string.IsNullOrWhiteSpace(value))
		{
			return "";
		}
		if (string.IsNullOrWhiteSpace(pattern))
		{
			throw new ArgumentException("pattern 参数不能为空");
		}
		value = Regex.Replace(value, pattern, replacement, options);
		return value;
	}

}

调用方法

static void Main(string[] args)
{
	string original = "NameNameemaNHello Name World!NameName";
	Console.WriteLine($"原字符串:{original}\r\n");
	Console.WriteLine($"移除指定字符串前后Name并重复匹配:{original.Trim("Name")}");
	Console.WriteLine(Environment.NewLine);
	Console.WriteLine($"移除指定字符串前后Name单次匹配：{original.Trim("Name", false)}");
	Console.WriteLine(Environment.NewLine);
	Console.WriteLine($"移除字符串开始Name并重复匹配：{original.TrimStart("Name")}");
	Console.WriteLine(Environment.NewLine);
	Console.WriteLine($"移除字符串开始Name不重复匹配：{original.TrimStart("Name", false)}");
	Console.WriteLine(Environment.NewLine);
	Console.WriteLine($"移除字符串结束Name并重复匹配：{original.TrimEnd("Name")}");
	Console.WriteLine(Environment.NewLine);
	Console.WriteLine($"移除字符串结束Name不重复匹配：{original.TrimEnd("Name", false)}");
	Console.Read();
}
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