How to make validation username using preg_match?

Question

I would like to create a preg_match function to validate my username, my code below not working perfectly, especially on Must contain at least 4 letter lowercase rules and number not more than 4 character and place behind letter

if (preg_match('/^[a-z0-9]{4,12}/', $_POST['username']))

Here are my username rules that I want to work :

Only contain letter and numbers but number is not reqired
Must contain at least 4 letter lowercase
Number not more than 4 character and place behind letter
Must be 4-12 characters

Thank you for any help you can offer.

can sites stop forcing me to abide by arbitrary rules for my user-name please. — , Feb 05 '18 at 01:15
Tell us; what isn't working the way you'd like it to? What results are you presently getting, as opposed to the desired results? You didn't describe the problem. — Funk Forty Niner, Feb 05 '18 at 01:18
we don't read minds, please remember that in case you're still here. I myself have left since it's unclear what it is you're asking. — Funk Forty Niner, Feb 05 '18 at 01:26
Take a look at https://stackoverflow.com/a/19605207/4333555, it's not exactly what your asking but it can lead you there. Also don't forget closing anchor. — chris85, Feb 05 '18 at 01:28
@chris hey stranger, long time no see. Hope all is well your way, *cheers* (I only revisited this post to see if there was any update/comments left). Alas, no. — Funk Forty Niner, Feb 05 '18 at 02:10
@FunkFortyNiner Ah, helllo Fred. Yea, kinda getting busy with side projects, havent been around much. — chris85, Feb 05 '18 at 19:02
@chris85 Kind of the same here; got me a fine issue with a server moving to a new location and has been a sort of nightmare but I am managing. There's always more than one way to skin a cat, as it were ;-) I didn't think you'd know who I was, given I changed my profile name; it's more fitting for me *lol!* cheers man, take care. — Funk Forty Niner, Feb 05 '18 at 19:03

score 1 · Accepted Answer · answered Feb 05 '18 at 10:02

You match these criteria, maybe this will be an option:

^[a-z](?=(?:[a-z]*\d){0,4}(?![a-z]*\d))(?=[a-z\d]{3,11}$)[a-z\d]+$

This will match

From the beginning of the string ^
Match a lowercase character [a-z]
A positive lookahead (?= which asserts that what follows is
- A non capturing group (?:
- Which will match a lowercase character zero or more times followed by a digit [a-z]*\d
- Close non capturing group and repeat that from 0 to 4 times ){0,4}
- A negative lookahead (?! Which asserts that what follows is not
- A lowercase character zero or more times followed by a digit [a-z\d]*
- Close negative lookahead )
Close positive lookahead )
Positive lookahead (?= which asserts that what follows is
- Match a lowercase character or a digit from 3 till 11 times till the end of the string (?=[a-z\d]{3,11}$)
Close positive lookahead )
Match a lowercase character or a digit till the end of the string [a-z\d]+$

Out php example

Srdjan M. · Answer 2 · 2018-02-05T02:29:04.967

Regex: ^[a-z]{4,8}[0-9]{0,4}$|^[a-z]{4,12}$

Details:

^ Asserts position at start of a line
$ Asserts position at the end of a line
[] Match a single character present in the list
{n,m} Matches between n and m times
| Or

PHP code:

$strings=['testtesttest', 'testtesttestr', 'test12345', 'testtest1234', 'testte123432'];

foreach($strings as $string){
    $match = preg_match('~^[a-z]{4,8}[0-9]{0,4}$|^[a-z]{4,12}$~', $string);
    echo ($string . ' => len: (' . strlen($string) . ') ' .($match ? 'true' : 'false')."\n");
}

Output:

testtesttest => len: (12) true
testtesttestr => len: (13) false
test12345 => len: (9) false
testtest1234 => len: (12) true
testte123432 => len: (12) false

Code demo

How to make validation username using preg_match?

2 Answers2