Regex for a Phone number and Extension only

Question

I've attempted multiple times to write a regex field validator for an asp.net intranet form web form. I've tried to tweek mine with no success. The current one i'm using and attempting to edit is

((\(\d{3}\) ?)|(\d{3}-))?\d{3}-\d{4} 

I need to be able to allow.

x1245
508-555-1212
5085551212
508 555 1212
508-555-1212 x1234
5085551212 x1243
508 555 1212 x1234

The only one i have covered is the second one on the list is the second one down.

Answer 1

This will do it.

(\d\d\d-?\s?\d\d\d-?\s?\d\d\d\d\s?)?(x\d\d\d\d)?

or shorter equivalent:

(\d{3}-?\s?\d{3}-?\s?\d{4}\s?)?(x\d{4})?

You want to match the full phone number, optionally with space/dash, and make that whole thing optional, then include extension, and make that optional too.

Answer 2

A pattern like this would match all your inputs:

\d{3}[- ]?\d{3}[- ]?\d{4}( x\d{4})?|x\d{4}

This will match either:

• three digits
• an optional space or hyphen
• three digits
• an optional space or hyphen
• four digits

• an optional group of:

  • a space, and a literal x
  • four digits

  —or—

• a space, and a literal x
• four digits

Depending on your precise needs, you may need to start (^) and end ($) anchors to prohibit extra characters around your pattern (e.g. "foo x1234 bar"):

^\d{3}[- ]?\d{3}[- ]?\d{4}( x\d{4})?|x\d{4}$

Update

If you'd like to ensure that the digit two separators between the three phone number segments must be the same—e.g. 508-555 1212 would not be allowed—the easiest way would be something like this:

\d{3}([- ]?)\d{3}\1\d{4}( x\d{4})?|x\d{4}

The (...) creates a capture group, and because it happens to be the first one in the pattern, it's referred to as group 1. The \1 is a backreference, which will only match the exact string which was matched in group 1.

Answer 3

This one quite complicated but will match

var regex = new Regex(@"^(?<number>\d{3}(?<separator>([\s-]|))\d{3}\k<separator>\d{4})?" +
                       "((?<=\d)\s|(?<=^)|(?=$))" +
                       "(?<extension>x\d{4})?(?<=.)$");

• ^ start of string
• (?<number> start named group number
• \d{3} match 3 digits
• (?<separator> start named group separator
• ([\s-]|) match space, - or empty string
• ) close group seperator
• \d{3} match 3 digits
• \k<separator> match previous separator
• \d{4} match 4 digits
• ) close group number
• ? previous match is optional
• ((?<=d)\s|(<=^)|(?=$)) previous char is a digit and match space, or match zero length if at start or end of string
• (?<extension>) start named group extension
• x\d{4} match x followed by 4 digits.
• ) close group extension
• ? extension group is optional
• (?<=.) zero length match that insures string isn't empty
• $ match end of string