Catch repeat letters in PHP - Regular expressions

Question

I have to check user input to make sure name, last name (etc...) are entered correctly and are valid. I have to build a regexp that check if a user enters repeated letters in the first name , last name etc...

Example:

AAAron = bad because of the 3 A's
AAron = good
Hannah = Good
Hannnah = bad because of the 3 N's

Is there a PHP regular expression to catch these cases? (I have a basic regexp knowledge but this is too much for me)

EDIT: This should Allow numbers as well: David 3 or III

Thanks

Is this really necessary? There should be no need to do more than validate i.e. the length of the name. If an user doesn't want to write his own name, he can just write anything down that'd be valid, such as "John Doe". In the contrary, your regexp might end up invalidating some more rare/exotic names. I wouldn't do this. — reko_t, Oct 25 '11 at 12:45
Possible duplicate of [How can I find repeated letters with a Perl regex?](http://stackoverflow.com/questions/178837/how-can-i-find-repeated-letters-with-a-perl-regex) — breiti, Oct 25 '11 at 12:47
Agreed with @WesleyvanOpdorp - see also my answer here: http://stackoverflow.com/questions/3853346/how-to-validate-human-names-in-cakephp/3853820#3853820 — Spudley, Oct 25 '11 at 12:48
@WesleyvanOpdorp someone that got a project which specific requirement. Have you heard about the name: AAAAAAAAron? very popular these days — Tech4Wilco, Oct 25 '11 at 12:59
What about my friend LLywellyn? Is he not allowed to join your site? — DaveRandom, Oct 25 '11 at 12:59
Nope, both are valid. Google it (and ignore the `Did you mean?`). — DaveRandom, Oct 25 '11 at 13:01
I've got a baby names book on my shelf, and out of curiosity, I decided to scan through it to see if there are any names in it that break your rules. It's taken me ten minutes to find "Saarrah". Apparently it's a derivative of "Sarah". I wouldn't name *my* child like that, but if it's common enough to be in the book, then you can bet there are at least a few people out therewith that name. I also found "Aarron" in the book. I'm not going to spend any more time looking, but I'd give good odds on there being quite a few more examples in there. — Spudley, Oct 25 '11 at 13:02
@DaveRandom never heard but I will agree with you it's a valid name, I updated my request thanks — Tech4Wilco, Oct 25 '11 at 13:02
Downvoting to -3 seems a bit harsh, this may not be the best idea in the world but it's a valid and clearly phrased question. I don't think downvoting on SO is meant for when you disagree with the idea. — Michael Low, Oct 25 '11 at 13:04
Since [there is a guy who legally changed his name to 'PlayStation 2'](http://news.bbc.co.uk/cbbcnews/hi/uk/newsid_1844000/1844194.stm), I don't think you can apply any rules to this. Presumably you were also planning to disallow numerics? — DaveRandom, Oct 25 '11 at 13:10
@DaveRandom I will have to allow numeric yes for David III (example) — Tech4Wilco, Oct 25 '11 at 13:16

RageZ · Accepted Answer · 2011-10-25T12:57:16.470

You can use back reference for that purpose.

preg_match('/(\w)(\1+)/', $subject, $matches);
print_r($matches);

the \1 means repeat the first capture so in that case \w.

In the case of your example, I don't think using regular expression would be the best solution, why don't you just count the number of instance of any characters?

i.e.

$charCountArray = array();
foreach ($name as $char) {
    $charCountArray[$char]++;
}

back reference is an advanced feature, luckily the PCRE functions supports it.

Note: preg_match would match only one sequence, if you need to know all the matches please use preg_match_all

score 5 · Answer 2 · answered Oct 25 '11 at 12:45

5

Try this regular expression:

/(\w)\1{2}/

answered Oct 25 '11 at 12:45

Aziz Shaikh

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Catch repeat letters in PHP - Regular expressions

2 Answers2