Regular expression for US and Canada phone number

This a quick post regarding how to validate US and Canada phone number in very possible formats.

Requirements:

To determine whether a user entered a North American phone number in a common format, including the local area code. The supported formats are 1234567890, 123-456-7890, 123.456.7890,  123 456 7890, (123) 456 7890, and all related combinations. If the phone number is valid, we will convert that our standard format,  (123) 456-7890, so that the phone number records are consistently recorded.

Suggested expression: ^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$

Valid phone number series for the expression:

• 123-456-7890
• 123 456-7890
• 123-456 7890
• (123)-456-7890
• 123 456 7890

.NET C# Code Snippet

string userInput = txtPhoneNumber.Text;

Regex regexPhoneNumber = new Regex(@"^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$");

if (regexPhoneNumber.IsMatch(userInput))
{
	string formattedPhoneNumber = regexPhoneNumber.Replace(userInput, "($1) $2-$3");
}
else
{
	// Invalid phone number
}

The following layout breaks the regular expression into its individual parts, excluding the repeating groups of digits:

Here, ‘^‘ and ‘$‘ are meta-characters named an anchor or assertion. ‘^ is used to mask the start of regular expression and $ is used to mark the end. ‘$’ is used to stop matching too much string into final result than required.

For people seeking more information regarding the expression are suggested to visit detailed post here: http://blog.stevenlevithan.com/archives/validate-phone-number

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