Valid domain name regex

Question

how should be valid domain name regex which full fill following criteria.

each label max 63 characters long minimum 1 characters
contains numbers, letters and '-', But
should not start and end with '-'
max domain name length 255 characters minimum 1.

for example

some of valid combinations:

a
a.com
aa-bb.b

I created this ^(([a-z0-9]){1,63}\.?){1,255}$

But currently its not validating '-' part as required (it's , missing)

Is there any way?

plz correct me if I am wrong.

use urlparse! Regex is not the answer to everything. – Games Brainiac Oct 31 '13 at 11:37 — Games Brainiac, Oct 31 '13 at 11:37

score 3 · Accepted Answer · answered Dec 08 '13 at 13:58

3

and mandatory to end with '.' : Here i found the solution

"^(((([A-Za-z0-9]+){1,63}\.)|(([A-Za-z0-9]+(\-)+[A-Za-z0-9]+){1,63}\.))+){1,255}$"

answered Dec 08 '13 at 13:58

Nikhil Rupanawar

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It doesn't have to end with a period. Mind explaining? A period normally comes in the last 2-4 characters of the domain, before the domain extension. – User Aug 18 '14 at 16:59
Yes, It is optional to have period at end. Needs improvement accordingly. – Nikhil Rupanawar Aug 19 '14 at 10:16
1

I decided to go with this: http://stackoverflow.com/questions/2532053/validate-a-hostname-string – User Aug 19 '14 at 20:22

score 2 · Answer 2 · answered Aug 29 '18 at 16:59

2

This expression should meet all the requirements: ^(?=.{1,255}$)(?!-)[A-Za-z0-9\-]{1,63}(\.[A-Za-z0-9\-]{1,63})*\.?(?<!-)$

uses lookahead for total character length
domain can optionally end with a .

answered Aug 29 '18 at 16:59

Steve Goossens

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toto_tico · Answer 3 · 2022-10-11T08:05:38.570

2

You can use a library, e.g. validators. Or you can copy their code:

Installation

pip install validators

Usage

import validators
if validators.domain('example.com')
    print('this domain is valid')

In the unlikely case you find a mistake, you can fix and report the error.

edited Oct 11 '22 at 08:05

answered Jan 28 '20 at 13:17

toto_tico

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score 1 · Answer 4 · answered Oct 31 '13 at 11:33

1

Maybe this:

^(([a-zA-Z0-9\-]{1,63}\.?)+(\-[a-zA-Z0-9]+)){1,255}$

answered Oct 31 '13 at 11:33

adam

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piokuc · Answer 5 · 2013-10-31T11:56:03.187

0

Don't use regex for parsing domain names, use urllib.parse.

If you need to find valid domain names in HTML then split the text of the page with a regex [ <>] and then parse each resulting string with urllib.parse.

edited Oct 31 '13 at 11:56

answered Oct 31 '13 at 11:23

piokuc

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urllib.parse will not ensure a valid domain name. the `netloc` could contain "localhost" or a false-positive of a malformed url ( e.g. "http://example", "http://malformed" ) – Jonathan Vanasco Jul 11 '14 at 23:08

score 0 · Answer 6 · answered Oct 31 '13 at 11:25

0

Use the | operator in your RE followed by the '-'.. ensure you escape the literal '-' with \

answered Oct 31 '13 at 11:25

user2878309

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Dropout · Answer 7 · 2020-07-03T22:08:27.147

0

Instead of using regex try to look at urlparse

https://docs.python.org/3/library/urllib.parse.html

It's fairly simple to learn and a lot better and comfortable to use.

edited Jul 03 '20 at 22:08

answered Oct 31 '13 at 11:39

Dropout

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Link is broken. – jmreicha Jul 02 '20 at 15:27
`urlparse()` accepts invalid domain names, try `urlparse("http://www.......example......com")` – hldev Mar 21 '23 at 17:47

score -1 · Answer 8 · edited Oct 12 '22 at 07:24

-1

Try this:

^(([a-z0-9]\-*[a-z0-9]*){1,63}\.?){1,255}$

edited Oct 12 '22 at 07:24

Arash Hatami

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answered Oct 31 '13 at 11:23

juankysmith

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Valid domain name regex

8 Answers8

Installation

Usage