Regular expression to match phone number?

Question

I want to match a phone number that can have letters and an optional hyphen:

• This is valid: 333-WELL
• This is also valid: 4URGENT

In other words, there can be at most one hyphen but if there is no hyphen, there can be at most seven 0-9 or A-Z characters.

I dont know how to do and "if statement" in a regex. Is that even possible?

Heiskell

An answer has been accepted, but I'd like to know: Can that hyphen be anywhere in the number, or must it always be (if at all) between the 3rd and 4th digit? – Chema

Is there a reason that you need to use a regex? – Exalted

@Carl Smotricz: it can be anywhere. good question. – Heiskell

@voyager: I'm writing the XSD restriction pattern facet. So yes, I need to use regex. – Heiskell

Answer 1

You seek the alternation operator, indicated with pipe character: |

However, you may need either 7 alternatives (1 for each hyphen location + 1 for no hyphen), or you may require the hyphen between 3rd and 4th character and use 2 alternatives.

One use of alternation operator defines two alternatives, as in:

({3,3}[0-9A-Za-z]-{4,4}[0-9A-Za-z]|{7,7}[0-9A-Za-z])

Prairial

Answer 2

I think this should do it:

/^[a-zA-Z0-9]{3}-?[a-zA-Z0-9]{4}$/

It matches 3 letters or numbers followed by an optional hyphen followed by 4 letters or numbers. This one works in ruby. Depending on the regex engine you're using you may need to alter it slightly.

Serdab

i have one question..so i tested the above regex, and it works fine. however, when i add more digits to the end, the regex validator still says it's valid. why is that? shouldnt the expression become invalid as soon as i add 1 more character? i test at tools.netshiftmedia.com/regexlibrary using 121333333 – Heiskell

@ShaChris23 because 121333333 also matches it at the beginning. For true full length matching, it'd be /^[a-zA-Z0-9]{3}-?[a-zA-Z0-9]{4}$/ (use the ^ and $ symbols to denote beginning of string and end of string (respectively)) – Postexilian

thank you, Dave! wow..I feel like I learned quite a bit from this one example. (^_^) – Heiskell

This is a really good answer. In some ways, it is better than my (accepted) answer. – Prairial

Answer 3

Not sure if this counts, but I'd break it into two regexes:

#!/usr/bin/perl

use strict;
use warnings;

my $text = '333-URGE';

print "Format OK\n" if $text =~ m/^[\dA-Z]{1,6}-?[\dA-Z]{1,6}$/;
print "Length OK\n" if $text =~ m/^(?:[\dA-Z]{7}|[\dA-Z-]{8})$/;

This should avoid accepting multiple dashes, dashes in the wrong place, etc...

Rootstock

Answer 4

Supposing that you want to allow the hyphen to be anywhere, lookarounds will be of use to you. Something like this:

^([A-Z0-9]{7}|(?=^[^-]+-[^-]+$)[A-Z0-9-]{8})$

There are two main parts to this pattern: [A-Z0-9]{7} to match a hyphen-free string and (?=^[^-]+-[^-]+$)[A-Z0-9-]{8} to match a hyphenated string.

The (?=^[^-]+-[^-]+$) will match for any string with a SINGLE hyphen in it (and the hyphen isn't the first or last character), then the [A-Z0-9-]{8} part will count the characters and make sure they are all valid.

Wanderoo

Note: I revised my answer after testing the regex. – Wanderoo

Answer 5

Thank you Heath Hunnicutt for his alternation operator answer as well as showing me an example.

Based on his advice, here's my answer:

[A-Z0-9]{7}|[A-Z0-9][A-Z0-9-]{7}

Note: I tested my regex here. (Just including this for reference)

Heiskell

This will consider 0------ to be valid. – Eisenstein

Answer 6

I use a or with two patterns 7 alpha numeric characters or 3 alpha numeric character a hyphen and 4 alpha numeric characters

def check_string(string):
    if re.match(r'^[A-Z0-9]{7}$|^[A-Z0-9]{3}-[A-Z0-9]{4}$', string):
        return True
    else:
        return False

Cooney