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C# in a Nutshell by Peter Drayton, Ted Neward, Ben Albahari

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Cookbook Regular Expressions

To wrap up this overview of how regular expressions are used in C# applications, the following is a set of useful expressions that have been used in other environments.[3]

  • Matching roman numerals:

    string p1 = "^m*(d?c{0,3}|c[dm])"
      + "(l?x{0,3}|x[lc])(v?i{0,3}|i[vx])$";
    string t1 = "vii";
    Match m1 = Regex.Match(t1, p1);
  • Swapping first two words:

    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);
  • Matching “keyword = value” patterns:

    string t3 = "myval = 3";
    string p3 = @"(\w+)\s*=\s*(.*)\s*$";
    Match m3 = Regex.Match(t3, p3);
  • Matching lines of at least 80 characters:

    string t4 = "********************"
      + "******************************"
      + "******************************";
    string p4 = ".{80,}";
    Match m4 = Regex.Match(t4, p4);
  • Extracting date/time values (MM/DD/YY HH:MM:SS):

    string t5 = "01/01/01 16:10:01";
    string p5 =
      @"(\d+)/(\d+)/(\d+) (\d+):(\d+):(\d+)";
    Match m5 = Regex.Match(t5, p5);
  • Changing directories (for Windows):

    string t6 =
      @"C:\Documents and Settings\user1\Desktop\";
    string r6 = Regex.Replace(t6,
      @"\\user1\\",
      @"\\user2\\");
  • Expanding (%nn) hex escapes:

    string t7 = "%41"; // capital A
    string p7 = "%([0-9A-Fa-f][0-9A-Fa-f])";
    // uses a MatchEvaluator delegate
    string r7 = Regex.Replace(t7, p7,
      HexConvert);
  • Deleting C comments (imperfectly):

    string t8 = @" /* * this is an old cstyle comment block */ "; string p8 = @" /\* # match the opening delimiter .*? # match a minimal numer ...

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