Regular expressions are used for searching and manipulating a large text. A regular expression check the following condition such as

·    To identify substrings that begins with or ends with a pattern of characters.

·    To find all words that begins with a group of character and end with some others characters.

·    Check the occurrence of a string pattern.

·    To modify one or more substrings and return them

It is also know as pattern string. It is the part of strings and it containing two types of characters.

·     Literals

·     and metacharacters

For example

“\bt” which means any word beginnings with t.

Where \b is metacharacter and t is the literals.

We used the namespace System.Text.RegularExpression for regular expression. Such namespace contain number of classes that can be used for searching and matching and modifying a text document. The important classes are

·         Regex

·         MatchCollection

·         Match

How uses these classes in our program

For example

using System; 
using System.Text; 
using System.Text.RegularExpressions;
class CheckRegExp 
{ 
    public static void Main() 
    { 
        string str; 
        str = "india,srilanka,nepal,berma"; 
        Regex reg = new Regex("|,"); 
        foreach (string s in reg.Split(str)) 
        Console.WriteLine(s); 
        Console.ReadLine(); 
    } 
}