Regular Expression Basics « Introduction « Regular Expressions

An item is either a single character or a complex structure of characters in square brackets.


using System;
using System.Text.RegularExpressions;


class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(Regex.Match("abcd", @"abcd?d").Success);  
        Console.WriteLine(Regex.Match("abcdc", @"abcd?d").Success); 
        Console.WriteLine(Regex.Match("abcdcd", @"abcd?d").Success);

    }
}

Element	Description
.	Specifies any character except a newline character (\n)
\d	Specifies any decimal digit
\D	Specifies any nondigit
\s	Specifies any whitespace character
\S	Specifies any non-whitespace character
\w	Specifies any word character
\W	Specifies any nonword character
^	Specifies the beginning of the string or line
\A	Specifies the beginning of the string
$	Specifies the end of the string or line
\z	Specifies the end of the string
\|	Matches one of the expressions separated by the vertical bar (pipe symbol)
[abc]	Specifies a match with one of the specified characters
[^abc]	Specifies a match with any one character except those specified
[a-z]	Specifies a match with any one character in the specified range
( )	Identifies a subexpression so that it's treated as a single element
?	Specifies one or zero occurrencesof the previous character or subexpression;
*	Specifies zero or more occurrences of the previous character or subexpression;
+	Specifies one or more occurrences of the previous character or subexpression;
{n}	Specifies exactly n occurrences of the preceding character or subexpression;
{n,}	Specifies a minimum of n occurrences of the preceding character or subexpression;
{n, m}	Specifies a minimum of n and a maximum of m occurrences of the preceding character;

Input Type	Regular Expression
Numeric input	^\d+$
Personal identification number (PIN)	^\d{4}$
Simple password	^\w{6,8}$
Credit card number	^\d{4}-?\d{4}-?\d{4}-?\d{4}$
E-mail address	^[\w-]+@([\w-]+\.)+[\w-]+$
HTTP or HTTPS URL	^https?://([\w-]+\.)+ [\w-]+(/[\w-./?%=]*)?$