Regex with min 8 digits, 20 characters

Question

I'm currently looking for a regex that verify's the following requirements:

Should contain atleast 8 digits (0-9).
Between the digits it is allowed to use other characters (a-z) (also upper case).
It should contain max 20 characters (a-z 0-9).

example:

12345678: true
123adafa45678: true
123ab456: false (needs atleast 8 digits, now only 6)
ab12345a678: true 
ab123456789afgb2459a2: false (more then 20 characters)

I tried serveral things but if I use something like: (\D*\d\D*){8,} then it works but it doesn't meet the last requirement (up to 20 characters).

Sorry, AngularJS but if I know how to write the regex it'll be allright I guess. — JeroenE, Dec 28 '16 at 13:51
It sounds like you're trying to write a password strength checker? Perhaps looking for existing third party libraries or standard password checking solutions would be better? The question is framed with very precise requirements, but you would be better off thinking at the wider level because precise requirements like this can easily end up changing later, but the overall need for a password checker will remain. — Simba, Dec 28 '16 at 14:03
No I was trying to verify if it meets the requirements for a number we use in our country to check if a company is a registered company. Password checkers wouldn't be such a problem. — JeroenE, Dec 28 '16 at 14:06

score 2 · Accepted Answer · answered Dec 28 '16 at 13:54

2

Use a lookahead for 8 digits:

^(?=(.*\d){8})[a-zA-Z\d]{8,20}$

See live demo.

answered Dec 28 '16 at 13:54

Bohemian

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This is a nice one, thank you! Works like a charm! Have to make two more so hopefully I'll understand it later today. :) – JeroenE Dec 28 '16 at 14:03
Yes, just it is advisable to replace `(.*\d){8}` with `(?:\D*\d){8}`. – Wiktor Stribiżew Dec 28 '16 at 14:04
Thanks Wiktor! Changed that. – JeroenE Dec 28 '16 at 14:05
@WiktorStribiżew your suggestion fails if there are multiple targets separated by newlines, because `\D` matches newlines but dot does not. See your version incorrectly matching [here](http://rubular.com/r/7bmdOzWgH9). – Bohemian Dec 28 '16 at 17:01
@Bohemian: The string that is passed to this regex cannot be a multiline string. It is a *password* validation. It does not matter whether you use `\D` or `.`. I suggested `(?:[a-z]*\d){8}` in my comment anyway. – Wiktor Stribiżew Dec 28 '16 at 17:25
@wiktor then the millionth of a second you'll save in "performance" using `\D` on such a tiny input isn't worth bothering about – Bohemian Dec 28 '16 at 17:29

Regex with min 8 digits, 20 characters

1 Answers1