Replacing substrings using Regex in C# .NET: phone number example

In this post we saw an application of Regex and Match to reformat date strings. Let’s check another example: change the following phone number formats…:

• (xxx)xxx-xxxx: (123)456-7890
• (xxx) xxx-xxxx: (123) 456-7890
• xxx-xxx-xxxx: 123-456-7890
• xxxxxxxxxx: 1234567890

…into (xxx) xxx-xxxx.

Here’s a possible solution:

private static string ReformatPhone(string phone)
{
	Match match = Regex.Match(phone, @"^\(?(\d{3})\)?[\s\-]?(\d{3})\-?(\d{4})$");
	return string.Format("({0}) {1}-{2}", match.Groups[1], match.Groups[2], match.Groups[3]);
}

If you call this function with any of the above 4 examples it will return “(123) 456-7890”.

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