Regex phone number

Question

I'm trying to solve a problem and i figure out that the best solution is to use regex.

I dont have advance knowledge on regex, so I really need your help.

The problem is that I need to identify if a string is phone number or a cell phone the way we use here in Brazil, like this:

The phone number could be in this format:

0 + XX + XXXXXXXX = 01121234567

Or

XX + XXXXXXXX = 1121234567

Or

XXXXXXXX = 21234567

In this case its a phone number, so it need to start with 2,3,4 or 5

And if its a cell phone it have 9 digits and must start with 9, exclusive, and second digit must be 6,7 or 8:

0 + XX + 9XXXXXXXX = 011961234567

Or

XX + 9XXXXXXXX = 11971234567

Or

9XXXXXXXX = 981234567

So, if i get the strings "011984160986", "11984160986" or "984160986", for example, I need to be able to identify that its a cell phone, and the same for phone numbers.

At the same time I must be able to check that string "84160289" its not a valid phone number.

Can anyone ligth me on this problem with a regex?

I not comfortable with use a lot of "ifs" in my code to validate this.

Thanks.

You say "second digit must be 6,7 or 8" but in the cell phone examples they don't do it. — logi-kal
– logi-kal, Commented Apr 26, 2017 at 12:35
"I'm trying to solve a problem and i figure out that the best solution is to use regex." Now you have two problems — Jeffery Thomas
– Jeffery Thomas, Commented Apr 26, 2017 at 14:10

logi-kal · Accepted Answer · 2017-04-26 13:51:27Z

1

The regex for the phone number is

\b(0?\d\d)?[2345]\d{7}\b

The regex for the cell phone number is

\b(0?\d\d)?9[678]\d{7}\b

The regex for validating both of them at the same time is

\b(0?\d\d)?([2345]|9[678])\d{7}\b

See demos: 1, 2, 3.

The \d escaper works depending on your language. If it does not work, try replacing it with [0-9].

edited Apr 26, 2017 at 13:51

answered Apr 26, 2017 at 12:38

logi-kal

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2 Comments

Raphael Telatim Over a year ago

Yes, the regex was exactly what I need, except one thing: I did some tests, and if I add a big number the regex did 2 matches, like regex101.com/r/0BI89u/1 . The \d{7} in the end doesnt mean that its allowed only 7 chars after this?

logi-kal Over a year ago

@RaphaelTelatim Oh, right. I've updated the answer using word boundaries (see https://regex101.com/r/0BI89u/2).

Jeffery Thomas · Accepted Answer · 2017-04-26 14:58:15Z

When I start working on a regex, I like to start with the simplest possible approach first.

NOTE 1: I like to use free spacing regexes. It helps with readability.

NOTE 2: I'm not using \d to avoid possible problems with unicode digits. If unicode digits are allowed, then use \d.

0 + XX + XXXXXXXX = 01121234567

0 [0-9]{2} [0-9]{8}

XX + XXXXXXXX = 1121234567

[0-9]{2} [0-9]{8}

XXXXXXXX = 21234567

[0-9]{8}

In this case its a phone number, so it need to start with 2,3,4 or 5

OK, now we have more restrictions. Let's start to narrow in here?

(0 [0-9]{2} [2-5] [0-9]{7} |
   [0-9]{2} [2-5] [0-9]{7} |
            [2-5] [0-9]{7})

With so much in common, we can compress that more.

(0 [0-9]{2} | [0-9]{2})? [2-5] [0-9]{7}

And finally compress again

(0? [0-9]{2})? [2-5] [0-9]{7}

And if its a cell phone it have 9 digits and must start with 9, exclusive, and second digit must be 6,7 or 8:

0 + XX + 9XXXXXXXX = 011961234567

0 [0-9]{2} 9 [6-8] [0-9]{7}

XX + 9XXXXXXXX = 11971234567

[0-9]{2} 9 [6-8] [0-9]{7}

9XXXXXXXX = 981234567

9 [6-8] [0-9]{7}

Combining them works the same

(0? [0-9]{2})? 9 [6-8] [0-9]{7}

Putting both phone and land lines together

((0? [0-9]{2})? [2-5]   [0-9]{7} |
 (0? [0-9]{2})? 9 [6-8] [0-9]{7})

This can be compressed to

(0? [0-9]{2})? ([2-5] | 9 [6-8]) [0-9]{7}

To embed this use word boundaries if that fits your needs.

\b (0? [0-9]{2})? ([2-5] | 9 [6-8]) [0-9]{7} \b

The final form is similar to the other answer, but I felt it's worthwhile to work the whole process.

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