Some Regular Expression

using System.Text.RegularExpressions

Roman Numbers

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);

Keyword = Value

string t3 = "myval = 3";

string p3 = @"(\w+)\s*=\s*(.*)\s*";;

Match m3 = Regex.Match(t3, p3);

Line of at Least 80 Characters

string t4 = "********************"

+ "******************************"

+ "******************************";

string p4 = ".{80,}";

Match m4 = Regex.Match(t4, p4);

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 of chracters

\*/ # match the closing delimiter

";

string r8 = Regex.Replace(t8, p8, "", "xs");

Removing Leading and Trailing Whitespace

string t9a = " leading";

string p9a = @"^\s+";

string r9a = Regex.Replace(t9a, p9a, "");

string t9b = "trailing ";

string p9b = @"\s+";

string r9b = Regex.Replace(t9b, p9b, "");

Turning '\' Followed by 'n' Into a Real Newline

string t10 = @"\ntest\n";

string r10 = Regex.Replace(t10, @"\\n", "\n");

IP Address

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);

Removing Leading Path from Filename

string t12 = @"c:\file.txt";

string p12 = @"^.*\\";

string r12 = Regex.Replace(t12, p12, "");

Joining Lines in Multiline Strings

string t13 = @"this is

a split line";

string p13 = @"\s*\r?\n\s*";

string r13 = Regex.Replace(t13, p13, " ");

Extracting All Numbers from a String

string t14 = @"

test 1

test 2.3

test 47

";

string p14 = @"(\d+\.?\d*|\.\d+)";

MatchCollection mc14 = Regex.Matches(t14, p14);