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Using RegexOptions

The RegexOptions flags enum lets you tweak matching behavior.

A common use for RegexOptions is to perform a case-insensitive search:


using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(Regex.Match("a", "A", RegexOptions.IgnoreCase)); 
    }
}

The output:

Most of the RegexOptions flags can be activated within a regular expression itself, using a single-letter code as follows:


using System;
using System.Text.RegularExpressions;


class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(Regex.Match("a", @"(?i)A"));

    }
}

The output:

You can turn options on and off throughout an expression as follows:


using System;
using System.Text.RegularExpressions;


class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(Regex.Match("AAAa", @"(?i)a(?-i)a"));
    }
}

The output:

Aa

Regular expression options and Regular expressions code

RegexOptions Enum value	Regular expressions code
IgnoreCase	i
Multiline	m
ExplicitCapture	n
Compiled	c
Singleline	s
IgnorePattern Whitespace	x
RightToLeft	r
ECMAScript	N/A
CultureInvariant	N/A

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