RegEx and validating telephone numbers

Question

I'm learning RegEx, and I'm stuck in the following exercise:

I must match:

1 (555) 555-5555
5555555555
1 555-555-5555
555-555-5555

and not:

1 555)555-5555
(6505552368)
10 (757) 622-7382
555)-555-5555

My expression (not working) is:

/([0-9]? ?)?(([0-9]{3})|(\([0-9]{3}\)))( |\-)?\2\5?\2[0-9]/ig

Could you please help me? I can't figure out what's wrong...

What is the difference between `1 (555) 555-5555` and `10 (757) 622-7382` ? — Jan, Apr 20 '16 at 15:20
@Jan: Sorry, I didn't say the first number, if present, must be 1 followed by a space — Alby11, Apr 20 '16 at 15:50
@S4rg0n alright. you can also see there : https://www.eclipse.org/tptp/home/downloads/installguide/gla_42/ref/rregexp.html — Shakiba Moshiri, Apr 20 '16 at 15:51

Jan · Answer 1 · 2016-04-20T15:33:25.780

1

You could come up with:

^\d\ *(?:\(\d+\))?[- \d]+$

See a demo on regex101.com.

Broken down:

^   - an anchor to bind the expression to the beginning of the line
\d  - one digit of 0-9
\ * - zero or more spaces
(?:\(\d+\))? - digits in parentheses, made optional
[- \d]+ - characters from the specified class
$ - bind the expression to the end

But quoting from the regex tag:

Since regular expressions are not fully standardized, all questions with this tag should also include a tag specifying the applicable programming language or tool.

Please update your question and apply the used programming language.

As pointed out by @Aminah, the given regex has flaws which can be avoided by using lookaheads, e.g.:

^(?!.*-{2,})\d\ *(?:\(\d+\))?[- \d]+$

The (?!.*-{2,}) makes sure that there are no two consequent slashes allowd.

edited Apr 20 '16 at 15:33

answered Apr 20 '16 at 15:21

Jan

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You are wrong. If you do it this way, how about `5555-----`?` – Aminah Nuraini Apr 20 '16 at 15:28
@AminahNuraini: You're right. I'd add a [negative lookahead](https://regex101.com/r/tZ9pP9/2) but the example was not in the original question. – Jan Apr 20 '16 at 15:31
He said telephone number. That's descriptive enough for that sample. – Aminah Nuraini Apr 20 '16 at 15:32
@AminahNuraini: Updated the answer. – Jan Apr 20 '16 at 15:33

Aminah Nuraini · Answer 2 · 2016-04-25T02:35:20.687

1

You can use this:

/^(\d? ?)?(\d{3}|\(\d{3}\))[ -]?\d{3}[ -]?\d+$/gm

Demo

Explanation:

^(\d? ?)?: ^ to match the very beginning of the string. \d is equal to [0-9]
(\d{3}|$\d{3}$): It's to match the second group where brackets are optional. You were right, but you put too many unnecessary parentheses.
[ -]?: It's equal to ( |-)?
\d+$: $ is for the end of the string.
/gm: m flag is for multiple lines

edited Apr 25 '16 at 02:35

answered Apr 20 '16 at 15:23

Aminah Nuraini

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Where is the case insensitive modifier needed with numbers? – Jan Apr 20 '16 at 15:28
We don't need it, but I forgot to delete it from the original regex the asker wrote – Aminah Nuraini Apr 20 '16 at 15:29
@AminahNuraini: Thank you!!! I tried to repeat a capturing group 555 = ([0-9]{3}) = group #3 and ( |\-) = #5 but it didn't work. Could you please tell me what is wrong? – Alby11 Apr 20 '16 at 15:54
it should be group 2. You count it wrong. – Aminah Nuraini Apr 20 '16 at 15:58
I meant my (wrong) example – Alby11 Apr 20 '16 at 16:12
1

Sorry, I tried, but it's confusing for me too – Aminah Nuraini Apr 20 '16 at 16:18

score 1 · Answer 3 · answered Apr 20 '16 at 15:29

Ok this one is bit tricky, to test actually.

Here you go:

^(\d\s?(?:\(\d{3}\))?\s?[\d|\-]{8,12})$

This one catches the full numbers only and returns the complete number, not the partials like others mentioned in other answers.

Test here:

https://regex101.com/r/hI5vT2/2

RegEx and validating telephone numbers

3 Answers3

Explanation: