RegexOptions.IgnoreCase

Sometimes text data has inconsistent casing. Some data is uppercase, and some lowercase, but both are valid.

The Regex type in the C# language by default is case-sensitive. But RegexOptions.IgnoreCase, an enum value, relaxes this.

Example

The RegexOptions enum is a Regex argument. This example shows how RegexOptions.IgnoreCase affects the result of the IsMatch method on an input that is in a different case.

using System;
using System.Text.RegularExpressions;

// The input string has an uppercase trailing letter.
const string value = "carroT";

// Print result of IsMatch method:
// ... With IgnoreCase;
// ... And without any options set.
Console.WriteLine(Regex.IsMatch(value, "carrot", RegexOptions.IgnoreCase));
Console.WriteLine(Regex.IsMatch(value, "carrot"));
True
False

Other methods

You can use RegexOptions.IgnoreCase with other methods, not just IsMatch. Try it with Split, Matches and Match. It has the same effect when used with these methods.

RegexOptions.IgnoreCase will relax the requirements for an input with letters to be matched. Thus, the input string can have a capital or lowercase letter.

Final note

The RegexOptions.IgnoreCase argument is useful in many regular expressions. Before using ToLower(), consider using IgnoreCase.