为了能够更好地理解如何在C#环境中使用正则表达式，这里整理了一些常用的正则表达式：

罗马数字：

string p1 = “^m*(d?c{0,3}|c[dm])” + “(l?x{0,3}|x[lc])(v?i{0,3}|i[vx])$”;
string t1 = “v”;
Match m1 = Regex.Match(t1, p1);

交换前两个单词位置：

string t2 = “the quick brown fox”;
string p2 = @”(\S+)(\s+)(\S+)”;
Regex x2 = new Regex(p2);
string r2 = x2.Replace(t2, “$3$2$1”, 1);

关健字=值：

string t3 = “myval = 3”;
string p3 = @”(\w+)\s=\s(.)\s$”;
Match m3 = Regex.Match(t3, p3);

实现每行80个字符：

string t4 = “********************”
+ “******************************”
+ “******************************”;
string p4 = “.{80,}”;
Match m4 = Regex.Match(t4, p4);
月/日/年 小时:分:秒的时间格式：

string t5 = “01/01/01 16:10:01”;
string p5 = @”(\d+)/(\d+)/(\d+) (\d+):(\d+):(\d+)”;
Match m5 = Regex.Match(t5, p5);
改变目录（仅适用于Windows平台）：

string t6 = @”C:\Documents and Settings\user1\Desktop”;
string r6 = Regex.Replace(t6,@”\user1\”, @”\user2\”);
扩展16位转义符：

string t7 = “%41”; // capital A
string p7 = “%([0-9A-Fa-f][0-9A-Fa-f])”;
string r7 = Regex.Replace(t7, p7, HexConvert);
删除C语言中的注释（有待完善）：

string t8 = @”
  /*
   * 传统风格的注释
   */
  ”;

  string p8 = @”
   /* # 匹配注释开始的定界符
   .*? # 匹配注释
   */ # 匹配注释结束定界符
  ”;
  string r8 = Regex.Replace(t8, p8, “”, “xs”);
删除字符串中开始和结束处的空格：

string t9a = ” leading”;
string p9a = @”^\s+”;
string r9a = Regex.Replace(t9a, p9a, “”);
string t9b = “trailing “;
string p9b = @”\s+$”;
string r9b = Regex.Replace(t9b, p9b, “”);
在字符\后添加字符n，使之成为真正的新行：

string t10 = @”\ntest\n”;
string r10 = Regex.Replace(t10, @”\n”, “\n”);
转换IP地址：

string t11 = “55.54.53.52”;
string p11 = “^” +
   @”([01]?\d\d|2[0-4]\d|25[0-5]).” +
   @”([01]?\d\d|2[0-4]\d|25[0-5]).” +
   @”([01]?\d\d|2[0-4]\d|25[0-5]).” +
   @”([01]?\d\d|2[0-4]\d|25[0-5])” +
   “$”;
Match m11 = Regex.Match(t11, p11);
删除文件名包含的路径：

string t12 = @”c:\file.txt”;
string p12 = @”^.*\”;
string r12 = Regex.Replace(t12, p12, “”);
联接多行字符串中的行：

string t13 = @”this is
  a split line”;
string p13 = @”\s\r?\n\s“;
string r13 = Regex.Replace(t13, p13, ” “);
提取字符串中的所有数字 ：

string t14 = @”
  test 1
  test 2.3
  test 47
  ”;
string p14 = @”(\d+.?\d*|.\d+)”;
MatchCollection mc14 = Regex.Matches(t14, p14);
找出所有的大写字母：

string t15 = “This IS a Test OF ALL Caps”;
string p15 = @”(\b[^\Wa-z0-9_]+\b)”;
MatchCollection mc15 = Regex.Matches(t15, p15);
找出小写的单词：

string t16 = “This is A Test of lowercase”;
string p16 = @”(\b[^\WA-Z0-9_]+\b)”;
MatchCollection mc16 = Regex.Matches(t16, p16);
找出第一个字母为大写的单词：

string t17 = “This is A Test of Initial Caps”;
string p17 = @”(\b[^\Wa-z0-9_][^\WA-Z0-9_]*\b)”;
MatchCollection mc17 = Regex.Matches(t17, p17);
找出简单的HTML语言中的链接：

string t18 = @”
  
  <a href=””first.htm””>first tag text
  <a href=””next.htm””>next tag text
  
  ”;
string p18 = @”<A[^>]?HREF\s=\s*[“”‘]?” + @”([^'”” >]+?)[ ‘””]?>”;
MatchCollection mc18 = Regex.Matches(t18, p18, “si”);

本文来自木庄网络博客> 开发中常用的正则表达式